EP2658879A2 - Method for modifying polymers comprising hydroxyl groups - Google Patents

Abstract

The invention relates to a method for reacting polymers (A) comprising hydroxyl groups and which have repetitive structural units of general formula (I), wherein D represents a direct bond between the polymer backbone and a hydroxyl group, a C₁-to C₆-alkene group, a C₅- to C₁₂-arylene group, an oxyalkylene group of formula -O-R²-, an ester group of formula -C(O)-O-R²- or an amide group of formula -C(O)-N(R⁸)R²-, R² represents a C₂- to C₁₀-alkene group, R⁸ represents hydrogen or an optionally substituted C₂- to C₁₀-alkyl group and n represents a number between 3 and 5000, with carboxylic acids B1 ) of formula (II) or carboxylic acid esters B2) of formula (III) R¹-COOH (II) R¹-COOR⁷ (III), wherein R¹ represents a hydrocarbon group having 2 to 50 C atoms, and R⁷ represents a C₁C₄-alkyl group, in which the polymers (A) comprising the hydroxyl groups are exposed to microwaves in the presence of carboxylic acids of formula (II) or carboxylic acid esters of formula (III) and in the presence of water. The reaction mixture is heated to temperatures over 100 °C by microwave rays.

Description

 description

The present invention relates to a process for modifying hydroxyl group-carrying addition polymers by polymer-analogous esterification of aqueous solutions of the polymers in the microwave field.

Higher molecular weight synthetic polymers bearing a variety of hydroxyl groups, such as poly (vinyl alcohol), are nonionic, water-soluble, thermoplastics that transition to highly viscous masses above their melting point. The water solubility of the polymers is dependent inter alia on the concentration of hydroxyl groups in the polymer and in

special case of poly (vinyl alcohol) also a function of the degree of hydrolysis of the poly (vinyl acetate) used in its preparation. For example, poly (vinyl alcohol) of high degree of hydrolysis is highly crystalline and soluble only in hot water. Poly (vinyl alcohol) has interesting physicochemical

Properties such as film and film formation, emulsifying behavior and adhesion make it interesting for a large number of technical applications. Furthermore, it has a very high tensile strength, which deviates with increasing moisture content such as increasing humidity of increasing elasticity, which is noticeable for example in a greater elasticity of films. By chemical modification, the properties of hydroxyl-bearing polymers can be influenced within wide limits. So can

For example, by hydrophobic modification their resistance to chemicals and solvents as well as their temperature stability can be improved. On the other hand, in the case of poly (vinyl alcohol), for example, after hydrophobic modification, the tensile strength is maintained even at high atmospheric humidity without losing water solubility. In particular by modification with longer-chain alkyl radicals, the polymers undergo a

application-wise very interesting inner plasticization. For different Applications, for example in the paper and textile industry, would be particularly advantageous in cold water less soluble polyvinyl alcohols, since they would improve the water resistance of surface applications. A common method for hydrophobing is, for example, the acetalization with aldehydes and especially with butyraldehyde.

However, aldehydes are chemically stable only to a limited extent, so that their handling requires special attention. Furthermore, the availability of

Aldehydes in particular with longer-chain alkyl radicals limited on an industrial scale, so that the breadth of the modification possibilities is very limited. In addition, the production of hydrophobically modified poly (vinyl alcohols) is associated with great technical complexity and thus high costs: With an aldehyde chain length of more than four carbon atoms, aldehydes become insoluble in water, which makes the washing out of excess aldehydes and the cleaning of the modified polymers extremely difficult. Also, the work-up

Excess aldehydes and especially excess aldehyde mixtures very expensive. Although such modified polymers are available in the laboratory, they are too expensive and expensive to produce on an industrial scale. In addition, at higher degrees of acetalization, and in particular in polymers with a low content of free OH groups, crosslinking of the polymers by intermolecular acetalization often takes place, which limits the applicability of this derivatization method.

Furthermore, prepare the different solubilities of polymer and

Derivatizing agent considerable preparative difficulties in the production of homogeneous products. For polymer-analogous reactions, the polymer to be reacted must be brought into a soluble or at least swollen form to ensure a homogeneous reaction. Is the polymer in the

Insoluble reaction medium, only surface reactions are possible; if the polymer is swollen in the reaction medium, the reaction rate depends on the accessibility of the functional groups in the pores of the polymer matrix. In partially crystalline polymers reactions take place practically only in the amorphous areas, since diffusion processes in the crystalline area are very are slow.

Hydroxyl-bearing polymers such as, for example, polyvinyl alcohol are in solvent-free form solids or highly viscous materials suitable for homogeneous chemical reactions. must be fluidized either thermally or by means of solvents. Preferred solvent for most hydroxyl-bearing polymers is water. For condensation reactions, however, water is usually less suitable as a solvent, since it is the

Reaction equilibrium shifts in favor of the educts. Although such polymers such as poly (vinyl alcohol) usually in polar aprotic solvents such as dimethyl sulfoxide, formamide, dimethylformamide and Phosphorsäuretrisdimethylamid solve. Upon removal of these high-boiling solvents after the reaction, the polymer usually suffers thermal damage, which makes them often unusable for further use.

According to DE-A-10 2009 001 382, hydroxyl-bearing polymers such as polyvinyl alcohol, polyvinyl acetal or their derivatives can also be hydrophobized or internally plasticized by reaction with alkylketene dimers. However, here too the choice of technically available

 Derivatization agent limited. The reaction is preferably carried out in organic solvents or solvent-free at temperatures above 100 ° C in the extruder. The preparation of corresponding (co) polymers by (co) polymerization longer-chain alkyl radicals carrying monomers with, for example, vinyl acetate are also limited, since suitable monomers such as

Alkylvinylester longer-chain carboxylic acids are technically limited and in most cases very expensive. In addition, in the subsequent hydrolysis of the acyl groups to hydroxyl groups, the long-chain esters are also at least partially hydrolyzed. Therefore, the industrial use of such hydrophobically modified hydroxyl-bearing polymers has hitherto been limited to a few applications. It would be desirable to modify water-soluble, hydroxyl-bearing and thus nonionic polymers with monofunctional ones

Reagents that are accessible inexpensively and in wide variation of their substituents and are not prone to cross-linking. A suitable method would be, for example, the esterification with monocarboxylic acids. According to the prior art, a polymer-analogous esterification is more hydroxyl-bearing

Polymers with hydrophobic, long-chain carboxylic acids with reactive

Acid derivatives such as acid anhydrides, acid chlorides or esters possible. However, at least equimolar amounts arise

 Carboxylic acids, salts or alcohols, which are to be separated and disposed of or work up and cause high costs. Since hydroxyl-carrying polymers such as poly (vinyl alcohol) are essentially only soluble in water, further undesirable by-products are formed by reaction of the reactive acid derivative with water. An esterification

 Hydroxyl-bearing polymers with free fatty acids in a direct way, on the other hand, problematic due to the different viscosities of polymers and acids and the insolubility of the polymers in organic solvents. According to US-2601561 succeed the esterification of poly (vinyl alcohol) with, based on the hydroxyl groups, at least equimolar amounts of ethylenically unsaturated carboxylic acids having at least 14 carbon atoms in

Solvents such as phenol, cresol or xylenol. The esterification requires temperatures between 150 and 250 ° C and takes 2 to 5 hours. The products obtained are intensely brown in color and contain on the one hand

high molecular crosslinked shares and on the other hand low molecular weight

 Degradation products. Even after workup, they still contain residual amounts of the low-volatile, toxicologically questionable solvents.

A recent approach to chemical synthesis are reactions in the microwave field. In this case, a significant acceleration of the reactions is often observed, which makes these methods both economically and ecologically very interesting. Thus, various esterifications of carbohydrates are disclosed in the prior art, almost invariably with carboxylic acid esters having a higher Reactivity than the free fatty acids have been carried out and still lead only to very low degrees of acylation. CN-1749279 teaches that when carbohydrates are reacted with acids at elevated temperature, degradation of the polymer also occurs, resulting in products with widely varying properties, depending on the feedstock used and the reaction conditions chosen.

It was therefore an object to provide a method for polymer-analogous modification of hydroxyl-carrying main chain polymers, with which the properties of said nonionic polymers can be modified in a simple and inexpensive manner in industrially interesting amounts. Of particular interest is the esterification of secondary hydroxyl-bearing linear addition polymers, and especially secondary ones

Hydroxyl-bearing linear addition polymers with only

C-C bonds built up backbone. In particular, crystallinity,

 Solubility in polar and non-polar solvents, thermal stability and / or plasticity of the polymers thereby be influenced. In order to achieve constant product properties both within a reaction batch as well as between different reaction mixtures, the modification should be as homogeneous as possible, that is to say in statistical distribution over the entire polymer. Furthermore, there should be no reactions on the polymer backbone, in particular polymer degradation, and no appreciable amounts of toxicologically and / or ecologically harmful by-products should arise.

Surprisingly, it has been found that higher molecular weight,

Hydroxyl-bearing polymers in aqueous solution and / or in solutions of water and water-miscible organic solvents with free carboxylic acids under the influence of microwaves at temperatures above 100 ° C esterify. In this way, hydroxyl-bearing polymers can be modified, for example, hydrophobic as well as hydrophilic. The

Solubility of such modified polymers gives no indication of this

Presence of larger hydrophilic or hydrophobic polymer blocks. There one Variety of different carboxylic acids is inexpensive and accessible in technical quantities, thus the properties of said polymers can be modified within wide limits. It does not lead to the degradation of the polymer chains. The invention accordingly provides a process for reacting hydroxyl-carrying polymers A), the repeating structural units of the general formula (I)

in which

D for a direct bond between polymer backbone and hydroxyl group, a C 1 to C 6 alkylene group, a C ₅ to C 3 arylene group, a

Oxyalkylene group of the formula -OR ² -, an ester group of the formula -C (O) -OR ² - or an amide group of the formula -C (O) -N (R ⁸ ) R ² -,

R ^{2 is} a C ² -C 10 -alkylene radical,

R ^{8 is} hydrogen or an optionally substituted C2 to

 Cio-alkyl radical and

n is a number between 3 and 5,000, with carboxylic acids B1) of the formula (II) or carboxylic esters B2) of the formula (III) R ¹ -COOH (II) R ¹ -COOR ⁷ (III) in which

R ^{1 is} a hydrocarbon radical having 2 to 50 C atoms, and

R ^{7 is} a C 1 -C ⁴ -alkyl radical in which hydroxyl-carrying polymers A) in the presence of carboxylic acids of the formula (II) or carboxylic acid esters of the formula (III) and in the presence of water are irradiated with microwaves, wherein the reaction mixture by the Microwave irradiation is heated to temperatures above 100 ° C.

Another object of the invention are esters of hydroxyl-bearing polymers prepared by reacting hydroxyl-bearing polymers A), the repetitive structural units of the general formula (I)

in which

D for a direct bond between polymer backbone and hydroxyl group, a Crbis Ce alkylene group, a C5 to C ^ arylene group, a

Oxyalkylene group of the formula -OR ² -, an ester group of the formula -C (O) -OR ² -, or an amide group of the formula -C (O) -N (R ⁸ ) R ² -, R ^{2 is} a C2 to C -io alkylene radical,

R ^{8 is} hydrogen or an optionally substituted C2 to

 Cio-alkyl radical and

n is a number between 3 and 5,000, with carboxylic acids B1) of the formula (II) or carboxylic esters B2) of the formula (III)

R is -COOH (II) R ¹ -COOR ⁷ (III) wherein

R ^{1 is} a hydrocarbon radical having 2 to 50 C atoms, and

R ^{7 is} a C 1 -C ₄ -alkyl radical, wherein hydroxyl-carrying polymers A) in the presence of carboxylic acids of the formula (II) or carboxylic acid esters of the formula (III) and in the presence of water are irradiated with microwaves and wherein the reaction mixture by the microwave irradiation to temperatures is heated above 100 ° C. Preferred hydroxyl-carrying polymers A are main chain polymers whose polymer backbone is composed only of C-C bonds and which

accordingly contains no heteroatoms. However, the preferred hydroxyl-carrying polymer A may contain groups with heteroatoms at the chain end which, for example, enter the polymer during the polymerization by the initiator and / or the moderator. Preferably, the polymer A contains a total of at least 5, more preferably at least 10, especially at least 15 and in particular at least 20 hydroxyl-carrying monomer units, d. H. n is at least 5, 10, 15 or 20. These

In the case of copolymers, monomer units may also be combined with or interrupted by structural units derived from other monomers.

D is preferably a direct bond between polymer backbone and

Hydroxyl group. The structural unit of the formula (I) is in this case from

Derived from vinyl alcohol. In a further preferred embodiment, D is a linear or branched alkylene radical. This preferably has one, two, three or four carbon atoms. These are, for example, structural units derived from allyl alcohol or from 3-buten-1-ol 3-buten-1-ol, 1-pentene-3-ol or 4-penten-1-ol. In a further preferred embodiment, D is an oxyalkylene group in which R ^{2 is} preferably an alkylene group having two, three or four C atoms. Such structural units (I) are preferably derived from hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether or

Hydroxybutylvinylether from. In another preferred embodiment, D is an ester group. Preferably, R ^{2 is} an alkylene group with 2 or

3 C atoms. Such structural units (I) are derived, for example, from

 Hydroxyalkyl esters of acrylic acid and methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and

Hydroxypropyl methacrylate from. In a further preferred embodiment, D is an amide group which is connected via a group R ² to the hydroxyl group. R ² here preferably stands for an alkyl group having 2 or 3 C atoms. R ⁸ may carry substituents such as a hydroxyl group. Preferably, R ^{8 is} hydrogen, methyl, ethyl or hydroxyethyl. such

Structural units (I) are derived, for example, from hydroxyalkylamides of Acrylic acid and methacrylic acid such as hydroxyethylacrylamide, hydroxyethylmethacrylamide, hydroxypropylacrylamide,

 Hydroxypropylmethacrylamid from. Also, several, for example, two, three, four or more different structural units of the formula (I) containing polymers are suitable according to the invention. The inventive method is

particularly suitable for the esterification secondary OH-bearing polymers.

Particularly preferred structural units of the formula (I) are derived from

From ethanol.

The inventive method is also suitable for the modification of

Copolymers of hydroxyl-carrying monomers, in addition to the

Hydroxyl-containing units of the formula (I) have structural elements derived from one or more other monomers which do not carry hydroxyl groups. Preferred further monomers are olefins, esters and amides of acrylic acid and methacrylic acid, vinyl esters, vinyl ethers, vinylamines, allylamines and their derivatives. Examples of preferred comonomers are ethene, propene, styrene, methyl acrylate, methyl methacrylate and esters of acrylic acid and methacrylic acid with alcohols having 2 to 24 carbon atoms. Preferably included

Copolymers more than 10 mol%, more preferably 15-99.5 mol%, especially 20-98 mol%, especially 50-95 mol% such as

70-90 mol% of structural units (I) derived from a hydroxyl group-carrying monomer.

Examples of suitable copolymers A) are copolymers of vinyl alcohol with vinyl esters, in particular copolymers of vinyl alcohol with vinyl acetate, as are obtainable, for example, by partial saponification of polyvinyl acetate. Preferred are copolymers which in addition to vinyl alcohol 0.5 to 60 mol% and particularly preferably 1 to 50 mol% such as 1, 5 to 10 mol%

Contain vinyl acetate. Starting from partially hydrolyzed poly (vinyl acetate), terpolymers of vinyl acetate, vinyl alcohol and according to the invention with a carboxylic acid of the formula ## STR1 ## can thus also be prepared by the process according to the invention (II) and / or a carboxylic acid ester of the formula (III) esterified vinyl alcohol. Furthermore, ester groups present in copolymer A can be completely or partially transesterified in the process according to the invention. Examples of other suitable copolymers A) are copolymers of vinyl alcohol and ethylene, vinyl alcohol and styrene and copolymers

Hydroxyethyl methacrylate and methyl methacrylate.

Preferred copolymers A) are homogeneously soluble or at least swellable in water or solvent mixtures of water and water-miscible organic solvent at temperatures above 40 ° C., for example at 50 ° C., 60 ° C., 70 ° C., 80 ° C. or 90 ° C. , Furthermore, they are preferred with a

Concentration of at least 1 wt .-% and in particular 5 to 90 wt .-% such as 20 to 80 wt .-% at temperatures above 40 ° C as

for example, at 50 ° C, 60 ° C, 70 ° C, 80 ° C or 90 ° C homogeneous in water or solvent mixtures of water and water-miscible organic solvent soluble or swellable.

Particularly preferred hydroxyl-bearing backbone polymers A are poly (vinyl alcohols). Under poly (vinyl alcohols) are understood according to the invention both homopolymers of vinyl alcohol and copolymers of vinyl alcohol with other monomers. Particularly preferred copolymers are those which contain 0.5 to 20 mol%, preferably 1 to 15 mol% vinyl ester. These are usually prepared by polymerization or copolymerization of esters of vinyl alcohol with lower carboxylic acids and subsequent hydrolysis of the ester. Preferred ester of the vinyl alcohol is vinyl acetate. The

Hydrolysis of the polymers can be complete or partial.

Further particularly preferred copolymers are copolymers of ethylene and vinyl alcohol. Especially preferred are those which are 15-70 mol% and especially 20-60 mol%, such as 25-50 mol% of ethylene derived

Contain structural units. The weight-average molecular weight M _{w of} preferred polymers A, determined on acetylated samples by gel permeation chromatography and static light scattering, is preferably between 10,000 and 500,000, especially between 12,000 and 300,000 and in particular between 15,000 and 250,000 g / mol. The molecular weight of the modified polymers is according to their

Increased degree of esterification and the molecular weight of the acyl radical.

Carboxylic acids B1) are generally compounds which have at least one carboxyl group. Thus, the inventive method is also suitable for the reaction of carboxylic acids with, for example, two, three, four or more carboxyl groups. Preferred carboxylic acids have a

Carboxyl group. The carboxylic acids may be of natural or synthetic origin. Particular preference is given to those carboxylic acids which carry a hydrocarbon radical R ¹ having 2 to 30 C atoms and in particular having 3 to 24, for example having 4 to 22 C atoms. The hydrocarbon radical is preferably aliphatic, cycloaliphatic, aromatic or araliphatic. Of the

Hydrocarbon radical may carry one or more, for example two, three, four or more further substituents, for example alkoxy, for example methoxy, amide, cyano, nitrile, nitro, sulfonic acid and / or C 5 -C 20 -aryl groups, for example phenyl groups with the proviso that the

Substituents are stable under the reaction conditions and none

Side reactions such as elimination reactions go. The hydrocarbon radical R ¹ may also contain heteroatoms such as oxygen, nitrogen, phosphorus and / or sulfur, but preferably not more than one heteroatom per 2 C atoms.

In a first preferred embodiment, the carboxylic acids B1) carry aliphatic hydrocarbon radicals. Particularly preferred are aliphatic hydrocarbon radicals having from 2 to 36, in particular from 3 to 24 and especially from 6 to 22, for example from 10 to 20 carbon atoms. These aliphatic

Hydrocarbon radicals can be linear, branched or cyclic. The

Carboxyl group may be bonded to a primary, secondary or tertiary carbon atom. The hydrocarbon radicals can be saturated or unsaturated be. Unsaturated hydrocarbon radicals contain one or more and preferably one, two or three C =C double bonds. Preferably, any double bonds are not in conjugation to the carboxyl group. Thus, the process of the invention has especially for the preparation of esters

unsaturated and in particular polyunsaturated fatty acids, since the double bonds of the unsaturated fatty acids among the

Reaction conditions of the method of the invention are not attacked. In a particularly preferred embodiment, the aliphatic hydrocarbon radical is an unsubstituted alkyl or alkenyl radical. In a further particularly preferred embodiment, the aliphatic carries

 Carbon hydrogen radical one or more such as two, three or more of the above substituents.

Preferred cycloaliphatic hydrocarbon radicals are aliphatic

Hydrocarbon radicals having 2 to 24 and in particular having 3 to 20 carbon atoms. You can optionally one or more heteroatoms such as

Contain nitrogen, oxygen or sulfur. Especially preferred

Cycloaliphatic hydrocarbon radicals have at least one ring with four, five, six, seven, eight or more ring atoms. The carboxyl group is bound to one of the rings.

Suitable aliphatic or cycloaliphatic carboxylic acids B1) are

for example, propionic acid, butyric acid, isobutyric acid, pentanoic acid, iso-pentanoic acid, pivalic acid, hexanoic acid, cyclohexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, isononanoic acid, neononanoic acid, decanoic acid,

Isodecanoic acid, neodecanoic acid, undecanoic acid, neoundecanoic acid,

Dodecanoic acid, tridecanoic acid, tetradecanoic acid, 12-methyltridecanoic acid, pentadecanoic acid, 13-methyltetradecanoic acid, 12-methyltetradecanoic acid,

Hexadecanoic acid, 14-methylpentadecanoic acid, heptadecanoic acid,

15-methylhexadecanoic acid, 14-methylhexadecanoic acid, octadecanoic acid,

Isooctadecanoic acid, icosanoic acid, docosanoic acid and tetracosanoic acid, and myristoleic acid, palmitoleic acid, hexadecadienoic acid, delta-9-cis-heptadecenoic acid, oleic acid, petroselenic acid, vaccenic acid, linoleic acid, Linolenic acid, gadoleic acid, gondoic acid, icosadeic acid, arachidonic acid, cetoleic acid, erucic acid, docosadienoic acid and tetracenoic acid. Also suitable are natural fats and oils such as

Cottonseed, coconut, peanut, safflower, corn, palm kernel, rapeseed, castor, olive, mustard, soya, sunflower and tallow, bone and fish oil derived fatty acid mixtures. As fatty acids or

Fatty acid mixtures are also suitable for the process according to the invention are tall oil fatty acid and resin and naphthenic acids. In a further preferred embodiment, the carboxylic acids B1) carry aromatic hydrocarbon radicals R ¹ . Aromatic carboxylic acids are understood as meaning compounds which carry at least one carboxyl group bonded to an aromatic system (aryl radical). Under aromatic

Systems are understood to mean (4n + 2) π-electron cyclic, fully conjugated systems in which n is a natural integer and preferably 1, 2, 3, 4 or 5. The aromatic system may be mono- or polycyclic, such as di or tricyclic. The aromatic system is preferably made

Carbon atoms formed. In a further preferred embodiment, it contains, in addition to carbon atoms, one or more heteroatoms, such as

For example, nitrogen, oxygen and / or sulfur. Examples of such aromatic systems are benzene, naphthalene, phenanthrene, furan and pyridine. The aromatic system may carry, in addition to the carboxyl group, one or more, for example, one, two, three or more identical or different further substituents. Suitable further substituents are, for example, alkyl, alkenyl and halogenated alkyl radicals, hydroxy, hydroxyalkyl, alkoxy, halogen, cyano, nitrile, nitro and / or sulfonic acid groups. These may be attached at any position of the aromatic system. However, the aryl radical carries at most as many substituents as it has valencies. Preferred examples of aromatic carboxylic acids B1) are

Alkylarylcarboxylic acids such as alkylphenylcarboxylic acids. These are aromatic carboxylic acids in which the aryl group carrying the carboxyl group additionally carries at least one alkyl or alkylene radical. Particular preference is given to alkylbenzoic acids which have at least one alkyl radical having 1 to 20 C atoms and in particular 1 to 12 C atoms, such as 1 to

Bear 4 C atoms. Suitable aromatic carboxylic acids are, for example, benzoic acid, the various isomers of naphthalenecarboxylic acid, pyridinecarboxylic acid, the various isomers of methoxybenzoic acid, and o-toluic acid,

m-toluic acid, p-toluic acid, o-ethylbenzoic acid, m-ethylbenzoic acid,

p-ethylbenzoic acid, o-propylbenzoic acid, m-propylbenzoic acid,

p-Propylbenzoic acid, 3,4-dimethylbenzoic acid and m-sulfobenzoic acid.

In a further preferred embodiment, the carboxylic acids B1) carry araliphatic hydrocarbon radicals R ¹ . Such araliphatic carboxylic acids contribute at least one via an alkylene or alkenylene radical

aromatic system-bound carboxyl group. The alkylene or

 Alkenylene radical preferably has 1 to 10 C atoms and in particular 2 to

5 C atoms. It may be linear or branched, preferably it is linear. Preferred alkenylene radicals have one or more, such as one, two or three double bonds. The aromatic system is understood to mean the aromatic systems already defined above, to which at least one

Carboxyl group bearing alkyl radical is attached. The aromatic systems may in turn contain substituents such as, for example, halogen atoms, halogenated alkyl radicals, C ₁ -C 20 -alkyl, C ₂ -C 20 -alkenyl, C 1 -C ₅ -alkoxy, such as, for example, methoxy, ester, amide, cyano. , Nitrile, and / or nitro groups. Examples of preferred araliphatic carboxylic acids are

 Phenylacetic acid, (2-bromophenyl) acetic acid, 3- (ethoxyphenyl) acetic acid, 4- (methoxyphenyl) acetic acid, (dimethoxyphenyl) acetic acid,

2-phenylpropionic acid, 3-phenylpropionic acid, cinnamic acid and mixtures thereof. Also mixtures of different carboxylic acids are for use in the

inventive method suitable.

Polycarboxylic acids can also be used as carboxylic acid B1). there it comes at least partially to an esterification of the polycarboxylic acid with hydroxyl groups of different polymer chains, which can lead to an increase in the molecular weight. Preference is given to using polycarboxylic acids in a mixture with monocarboxylic acids. The proportion of polycarboxylic acids is preferably between 0.1 and 70 mol%, more preferably between 0.5 and 50 mol% and in particular between 1 and 20 mol%, for example between 2 and 10 mol%, based on the total amount the carboxylic acids used for the esterification. Preferred polycarboxylic acids have two, three, four or five carboxyl groups. Particularly preferred are dicarboxylic acids. Suitable polycarboxylic acids are aliphatic polycarboxylic acids such as

Malonic acid, succinic acid, maleic acid, fumaric acid, itaconic acid,

Dodecenylsuccinic acid, octadecenylsuccinic acid, butanetetracarboxylic acid, dimer fatty acid and trimer fatty acid and aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, naphthalenedicarboxylic acid,

Trimellitic acid, trimesic acid and pyromellitic acid.

The carboxylic acid esters B2) which are suitable according to the invention are esters of the abovementioned carboxylic acids B1) with alcohols of the general formula R ⁷ -OH. R ⁷ is preferably an alkyl radical having 1, 2 or 3 C atoms. Particularly preferred alcohols are methanol and ethanol.

Hydroxyl-carrying polymers A and carboxylic acids B1) or

Carboxylic esters B2) are preferably used in a ratio of 100: 1 to 1: 1, more preferably in a ratio of 10: 1 to 1, 1: 1 and especially in a ratio of 8: 1 to 1.2: 1, based in each case on the molar equivalents of hydroxyl groups Structures of the formula (I) and the carboxyl groups of the formulas (II), (III) and / or (IV). By the ratio of carboxylic acids B1) or carboxylic acid esters B2) to hydroxyl groups of the polymer, the degree of modification and thus the properties of the product can be adjusted. If carboxylic acid B1) or carboxylic acid ester B2) used in excess or not completely to

Reaction are brought, portions thereof remain unreacted in the polymer, which can remain depending on the purpose in the product or can be separated. The esterification of the free hydroxyl groups of the polymer A can accordingly completely or partially. In the case of partial esterification, preference is given to esterifying 1 to 99%, particularly preferably 2 to 90%, in particular 5 to 70% and especially 10 to 50%, for example 20 to 40%, of the hydroxyl groups.

Particularly preferred is the inventive method for the partial

Esterification of hydroxyl-carrying polymers (A) suitable. In this case, carboxylic acid B1) or carboxylic acid ester B2) based on the

Total number of hydroxyl groups preferably substoichiometrically used, in particular in the ratio 1: 100 to 1: 2 and especially in the ratio 1: 50 to 1: 5 such as in the ratio 1: 20 to 1: 8. Preference is given to

Reaction conditions thereby adjusted so that at least 10 mol%, in particular 20 to 100 mol% and especially 25 to 80 mol%, such as 30 to 70 mol% of the carboxylic acid or of the used

Be implemented fatty acid esters. In these partial esterifications very homogeneous products are formed, which manifests itself in good solubility and a sharp cloud point of aqueous solutions.

Preferably, the reaction mixture contains 5 to 98 wt .-%, particularly preferably 10 to 95 wt .-%, in particular 20 to 90 wt .-%, such as 50 to 80 wt .-% water, or 5 to 98 wt .-%, particularly preferably 10 to

95 wt .-%, in particular 20 to 90 wt .-% such as 50 to 80 wt .-% of a mixture of water and one or more water-miscible, organic solvent. In any case, water is added to the reactants A and / or B prior to irradiation with microwaves, so that the reaction product contains an amount of water in excess of the amount of water of reaction liberated during the esterification.

The limited solubility of various carboxylic acids B1) and carboxylic acid esters B2) in water often requires the addition of one or more water-miscible, organic solvents to the reaction mixture. Preferred water-miscible organic solvents are polar protic and polar aprotic liquids. Preferably, these have a measured at 25 ° C. Dielectric constant of at least 10 and in particular at least 12 such as at least 15. Preferred organic solvents are soluble in water to at least 100 g / l, more preferably at least 200 g / l, in particular at least 500 g / l and especially they are complete with water miscible. Particularly preferred solvents are heteroaliphatic

 Compounds and in particular alcohols, ketones, end-capped polyethers, carboxylic acid amides such as tertiary carboxylic acid amides, nitriles,

Sulfoxides and sulfones. Examples of preferred aprotic solvents are formamide, N, N-dimethylformamide (DMF), N, N-dimethylacetamide, acetone, γ-butyrolactone, acetonitrile, sulfolane and dimethyl sulfoxide (DMSO). Preferred protic organic solvents are lower alcohols having 1 to 10 C atoms and in particular having 2 to 5 C atoms. Examples of suitable alcohols are

Methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isoamyl alcohol, 2-methyl - 2-butanol, ethylene glycol and glycerin. Secondary and tertiary alcohols are particularly preferably used as lower alcohols, which are inert under the chosen reaction conditions and neither tend to competing esterification nor to side reactions such as dehydration. Particularly preferred are secondary and tertiary alcohols having 3 to 5 carbon atoms such as

Isopropanol, sec-butanol, 2-pentanol and 2-methyl-2-butanol and

Neopentyl. Also mixtures of the solvents mentioned are

suitable according to the invention.

In general, low-boiling liquids are preferred as the water-miscible, organic solvents and in particular those which have a boiling point at atmospheric pressure of below 150 ° C and especially below 120 ° C such as below 100 ° C and thus with little effort again from the

Reaction products can be removed. High-boiling solvents have proven particularly useful if they are for further use of the

modified polymers may remain in the product. If water-miscible organic solvents are used, their share in the

Solvent mixture preferably between 1 and 75 wt .-%, more preferably between 2 and 60 wt .-%, in particular between 5 and 50 wt .-% as for example, between 10 and 30 wt .-%. Water is contained in the solvent mixture ad 100 wt .-%.

When using carboxylic acids B1) or carboxylic acid esters B2) with limited water solubility, the reaction mixture in a preferred

 Embodiment one or more emulsifiers are added. Emulsifiers which are chemically inert towards the educts and the product are preferably used. In a particularly preferred embodiment, the emulsifier is a reaction product of separate ones

Production.

The preparation of the method used for the process according to the invention

A reaction mixture comprising a hydroxyl group-carrying polymer (A), a carboxylic acid B1) or a carboxylic acid ester B2), water and optionally a water-miscible solvent and / or other auxiliaries such

For example, contains emulsifier and / or catalyst, can be done in various ways. The mixing of polymer A) and carboxylic acid B1) or

Carboxylic ester B2) and optionally the other auxiliaries can be carried out continuously, batchwise or else in semi-batch processes. In particular for processes on an industrial scale, it has proven useful to supply the starting materials to the process according to the invention in liquid form. For this purpose, the hydroxyl-carrying polymer A) is preferably fed to the process according to the invention as a solution in water or as a solution in water and a water-miscible solvent. But it can also be used in swollen form, provided that it is pumpable.

The carboxylic acid B1) or the carboxylic acid ester B2), insofar as they are liquid or meltable at low temperatures of preferably below 150 ° C. and in particular below 100 ° C., can be used as such. In many cases, it has been found useful to use B1) or B2), optionally in the molten state, with water and / or a water-miscible solvent, for example as a solution, dispersion or emulsion. The mixing of hydroxyl-carrying polymer A) with carboxylic acid B1) or carboxylic acid ester B2) and optionally the other auxiliaries can be carried out in a (semi) -batch process by sequential charging of the constituents, for example in a separate stirred tank. In a preferred embodiment, the carboxylic acid or the carboxylic acid ester is dissolved in a water-miscible organic solvent and then added to the already dissolved or swollen polymer. Preferably, the addition is carried out in small portions over a long time and with stirring, on the one hand to ensure a homogeneous distribution of the carboxylic acid or carboxylic acid ester and on the other hand to avoid local precipitation of the polymer at the metering.

In particular, for continuously carried out reactions, the starting materials in a preferred embodiment in the desired ratio of separate templates to the vessel in which the irradiation with microwaves is carried out (hereinafter also referred to as a reaction vessel) fed. In a further preferred embodiment, they are further homogenized prior to entry into the reaction vessel and / or in the reaction vessel itself by means of suitable mixing elements such as static mixers and / or Archimedean screw and / or by flowing through a porous foam.

If used, a catalyst and further auxiliaries can be added to one of the educts or also to the educt mixture before it enters the reaction vessel. Solid, pulverulent and heterogeneous systems can also be reacted by the process according to the invention, with only corresponding technical devices for conveying the reaction mixture being required.

The reaction takes place according to the invention under the influence of

Microwave radiation, wherein the reaction mixture through the

Microwave radiation preferably at temperatures above 110 ° C, more preferably at temperatures between 120 and 230 ° C, in particular between 130 and 210 ° C and in particular between 140 and 200 ° C such as between 150 and 195 ° C is heated. These temperatures refer to the maximum temperatures reached during microwave irradiation. The temperature can be measured, for example, on the surface of the irradiation vessel. In continuous reactions, it is preferably determined on the reaction mixture directly after leaving the irradiation zone. The pressure in the reaction vessel is preferably set so high that the reaction mixture remains in the liquid state and does not boil. Preference is given to operating at pressures above 1 bar, preferably at pressures between 3 and 300 bar, more preferably between 5 and 200 and in particular between 10 and 100 bar, for example between 15 and 50 bar.

To accelerate or complete the reaction between polymer A) and carboxylic acid B1) or carboxylic acid ester B2), it has proven useful in many cases to work in the presence of acidic catalysts. Preferred catalysts according to the invention are acidic inorganic, organometallic or organic catalysts and mixtures of several of these catalysts. Preferred catalysts are liquid and / or soluble in the reaction medium.

Examples of acidic inorganic catalysts for the purposes of the present invention are sulfuric acid, phosphoric acid, phosphonic acid, hypophosphorous acid, aluminum sulfate hydrate, alum, acidic silica gel and acid

To call aluminum hydroxide. Furthermore, for example

Aluminum compounds of the general formula AI (OR ¹⁵ ) 3 and titanates of the general formula Ti (OR ¹⁵ ) 4 can be used as acidic inorganic catalysts, where the radicals R ^{15 can} each be identical or different and are selected independently of one another from d-Cio-alkyl radicals, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1, 2-dimethylpropyl, iso-amyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, 2-Ethylhexy, n-nonyl or n-decyl, _C3-Ci2 cycloalkyl, for example cyclopropyl, cyclobutyl, Cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl and cyclododecyl; preferred are cyclopentyl, cyclohexyl and cycloheptyl. The radicals R ⁵ in Al (OR ¹⁵ ) ₃ or Ti (OR ¹⁵ ) ₄ are preferably identical and selected from isopropyl, butyl and 2-ethylhexyl.

Preferred acidic organometallic catalysts are, for example, selected from dialkyltin oxides (R ¹⁵ ) ₂ SnO, where R ^{15 is} as defined above. A particularly preferred representatives of acidic organometallic catalysts is di-n-butyltin oxide, which is commercially available as so-called Oxo-tin or as Fascat ^® brands.

Preferred acidic organic catalysts are acidic organic compounds with, for example, sulfonic acid or phosphonic acid groups. Particularly preferred sulfonic acids contain at least one sulfonic acid group and at least one saturated or unsaturated, linear, branched and / or cyclic hydrocarbon radical having 1 to 40 carbon atoms and preferably having 3 to 24 carbon atoms. Particularly preferred are aromatic sulfonic acids and especially alkylaromatic mono-sulfonic acids with one or more

Ci-C ₂ 8-alkyl radicals and in particular those with C ₃ -C ₂ 2-alkyl radicals. Suitable examples are methanesulfonic acid, butanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, xylenesulfonic acid, 2-mesitylenesulfonic acid,

4-ethylbenzenesulfonic acid, isopropylbenzenesulfonic acid, 4-butylbenzenesulfonic acid, 4-octylbenzenesulfonic acid; dodecylbenzenesulfonic

 Didodecylbenzenesulfonic acid, naphthalenesulfonic acid. Also acid

Ion exchangers can be used as acidic organic catalysts, for example, crosslinked poly (styrene) resins carrying sulfonic acid groups. Particularly preferred for carrying out the process according to the invention are sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid,

Dodecylbenzenesulfonic acid, phosphoric acid, polyphosphoric acid and

Polystyrenesulfonic. Especially preferred are titanates of the general formula Ti (OR ¹⁵ ) ₄ and especially titanium tetrabutylate and titanium tetraisopropylate.

If you want acidic inorganic, organometallic or organic

Catalysts are used according to the invention 0.01 to 10 wt .-%, preferably 0.02 to 2 wt .-% catalyst. In a further preferred embodiment, the microwave irradiation is carried out in the presence of acidic, solid and in the reaction medium not or not completely soluble catalysts. Such heterogeneous

Catalysts can be suspended in the reaction mixture and exposed to microwave irradiation together with the reaction mixture. In a particularly preferred continuous embodiment, the

optionally mixed with solvent reaction mixture over an im

Reaction vessel and fixed in particular in the irradiation zone

Passed fixed bed catalyst while exposed to microwave radiation. Suitable solid catalysts are, for example, zeolites, silica gel, montmorillonite and (partially) crosslinked polystyrenesulphonic acid, which may optionally be impregnated with catalytically active metal salts. Suitable acid ion exchangers based on polystyrenesulfonic acids, which can be used as solid phase catalysts are, for example, from Rohm & Haas under the

Brand name Amberlyst ^® available.

To accelerate or complete the reaction between polymer A) and carboxylic acid ester B2), it has proven useful in many cases to work in the presence of basic catalysts or mixtures of several of these catalysts. Basic catalysts which are generally used in the context of the present invention are those basic compounds which are suitable for the transesterification of carboxylic acid esters with alcohols

To accelerate carboxylic acid esters. Examples of suitable catalysts are inorganic and organic bases such as metal hydroxides, oxides, carbonates or alkoxides. In a preferred embodiment, the basic catalyst is selected from the group of hydroxides, oxides,

Carbonates or alkoxides of alkali or alkaline earth metals. There are

Lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide,

Potassium methoxide, sodium carbonate and potassium carbonate are very particularly preferred. Cyanide ions are also suitable as catalyst. These substances can be used in solid form or as a solution, for example as an aqueous or alcoholic solution. The amount of catalysts used depends thereby from the activity and stability of the catalyst with the selected ones

Reaction conditions and must be adapted to the particular reaction. The amount of catalyst to be used can vary within wide limits.

Particular preference is given to using catalytic amounts of the abovementioned reaction-accelerating compounds, preferably in the range from 0.001 to 10% by weight, more preferably in the range from 0.01 to 5% by weight, for example from 0.02 to 2% by weight. -%, based on the amount of carboxylic acid ester B2). After microwave irradiation, the reaction mixture can in many cases be fed directly to further use. In order to obtain solvent-free products, water optionally present organic solvent can be separated from the crude product by conventional separation methods such as phase separation, distillation, freeze-drying or absorption. In this case, it is also possible to separate off any starting materials used in excess and, if appropriate, unreacted residual amounts of the educts. For special

Demands, the crude products by conventional purification methods such as washing, reprecipitation, filtration or chromatographic

Procedure be further purified. Often, it has also proved to be successful here to neutralize excess or unreacted carboxylic acid and remove by washing.

The microwave irradiation is usually carried out in devices which have a reaction vessel (also referred to below as irradiation vessel) made of a material that is largely transparent to microwaves, into which microwave radiation generated in a microwave generator is coupled. Microwave generators, such as the magnetron, the klystron and the gyrotron are known in the art. The used for carrying out the method according to the invention

 Reaction vessels are preferably made of largely microwave-transparent, high-melting material or contain at least parts such as

for example, windows made of these materials. Particularly preferred non-metallic reaction vessels used. Under largely

Microwave transparent here materials understood that absorb as little microwave energy and convert it into heat. As a measure of the ability of a substance to absorb microwave energy and convert it into heat is often the dielectric loss factor tan δ = ε'Ίε '

used. The dielectric loss factor tan δ is defined as the ratio of dielectric loss z ^" and dielectric constant ε '. Examples of tan δ values of different materials are described in D. Bogdal, for example.

Microwave-assisted Organic Synthesis, Elsevier 2005. For reaction vessels suitable according to the invention, materials with tan δ values measured at 2.45 GHz and 25 ° C. of less than 0.01, in particular less than 0.005 and especially less than 0.001 are preferred. Preferred microwave-transparent and temperature-stable materials are primarily mineral-based materials such as, for example, quartz, aluminum oxide, zirconium oxide, silicon nitride and the like. Also thermally stable plastics such as in particular fluoropolymers such as Teflon, and engineering plastics such

Polypropylene, or polyaryletherketones such as glass fiber reinforced polyetheretherketone (PEEK) are suitable as vessel materials. To the

In order to withstand temperature conditions during the reaction, in particular minerals coated with these plastics, such as quartz or aluminum oxide, have proven to be useful as vessel materials.

Microwaves are electromagnetic waves having a wavelength between about 1 cm and 1 m and frequencies between about 300 MHz and 30 GHz. This frequency range is in principle for the

inventive method suitable. For the inventive method, microwave radiation with frequencies released for industrial, scientific and medical applications is preferably used, such as

for example, at frequencies of 915 MHz, 2.45 GHz, 5.8 GHz or 24.12 GHz. The microwave irradiation of the reaction mixture can be carried out both in

Microwave applicators that operate in mono or quasi-single mode as well as in those working in multimode done. Corresponding devices are known to the person skilled in the art. The microwave power to be radiated into the reaction vessel for carrying out the process according to the invention depends in particular on the desired reaction temperature, the geometry of the reaction vessel and the reaction volume associated therewith and on the flow rate of the reaction

Reaction good through the reaction vessel. It is usually between 100 W and several 100 kW and in particular between 200 W and 100 kW such as between 500 W and 70 kW. It can be applied at one or more points of the reaction vessel. It can be generated by one or more microwave generators.

The duration of the microwave irradiation depends on various factors such as the reaction volume, the geometry of the reaction vessel, the desired residence time of the reaction mixture at the reaction temperature and the desired degree of conversion. Usually, the microwave irradiation for a period of less than 30 minutes, preferably between

0.01 second and 15 minutes, more preferably between 0.1 second and 10 minutes and in particular between one second and 5 minutes, for example between 5 seconds and 2 minutes. The intensity (power) of the microwave radiation is adjusted so that the

Reactive material in the shortest possible time reaches the desired reaction temperature. In a further preferred embodiment of the process according to the invention, it has proven useful to supply the reaction mixture to the reaction vessel in heated form. This lowers the viscosity of the reaction mixture and improves its homogeneity. To maintain the

Reaction temperature, the reaction mixture with reduced and / or pulsed power can be further irradiated or otherwise maintained at temperature. In a preferred embodiment, the reaction product is cooled as soon as possible after completion of the microwave irradiation to temperatures below 100 ° C, preferably below 80 ° C and especially below 50 ° C. The microwave irradiation can be carried out batchwise or, preferably, continuously, for example in a flow tube serving as a reaction vessel, which is also referred to below as the reaction tube. You can continue in semi-batch processes like

For example, continuously operated stirred reactors or cascade reactors are performed. In a preferred embodiment, the reaction is carried out in a closed, pressure-resistant and chemically inert vessel, wherein the water and optionally the educts lead to a pressure build-up. After completion of the reaction, the excess pressure can be used by venting to volatilize and separate water and optionally excess acid and / or cooling of the reaction product. In a particularly preferred embodiment, after termination of the microwave irradiation or after leaving the reaction vessel, the reaction mixture is freed as rapidly as possible from water and optionally present catalytically active species in order to avoid hydrolysis of the ester formed.

In a preferred embodiment, the process according to the invention is carried out in a discontinuous microwave reactor in which a certain amount of the reaction mixture is filled into an irradiation vessel, irradiated with microwaves and subsequently worked up. Here is the

 Microwave irradiation is preferably carried out in a pressure-tight, stirred vessel. The coupling of the microwaves in the reaction vessel can, if the reaction vessel is made of a microwave transparent material or has transparent windows for microwave over the

Vascular wall done. The microwaves can also be transmitted via antennas,

Probes or waveguide systems are coupled into the reaction vessel. For the irradiation of larger reaction volumes, a multimode microwave applicator is preferably used here. The discontinuous

Embodiment of the method according to the invention allows by varying the microwave power fast as well as slow heating rates and in particular holding the temperature for longer periods such as several hours. In a preferred embodiment, the aqueous

Reaction mixture before the microwave irradiation in the irradiation vessel submitted. It preferably has temperatures below 100 ° C as

for example between 10 and 50 ° C. In a further preferred

Embodiment, the reactants and water or parts thereof are supplied to the irradiation vessel only during the irradiation with microwaves. In a further preferred embodiment, the discontinuous

Microwave reactor with continuous feeding of educts and

operated simultaneously discharging reaction mixture in the form of a semi-batch or cascade reactor. In a particularly preferred embodiment, the process according to the invention is carried out in a continuous microwave reactor. The

Reaction mixture is to continuously by a pressure-resistant, inert to the reactants, for microwave largely transparent and built into a microwave applicator, serving as an irradiation vessel

Reaction tube out. This reaction tube preferably has a diameter of one millimeter to about 50 cm, especially between 2 mm and 35 cm, for example between 5 mm and 15 cm. Particularly preferred is the

Diameter of the reaction tube smaller than the penetration depth of the microwaves in the reaction mixture to be irradiated. In particular, it is 1 to 70% and especially 5 to 60% such as 10 to 50% of the penetration depth. Under penetration depth is understood here the route on which the irradiated

Microwave energy is attenuated to 1 / e.

Under reaction or flow tubes are understood here irradiation vessels, in which the ratio of length to diameter of the

 Irradiation zone (this is understood as the proportion of the flow tube in which the reaction mixture is exposed to microwave radiation) greater than 5, preferably between 10 and 100,000, more preferably between 20 and 10,000 such as between 30 and 1,000. For example, they can be straight or bent or shaped as a tube coil. In a specific embodiment, the reaction tube is in the form of a

Double jacketed tube designed by the inner and outer space, the reaction mixture can be performed in succession in countercurrent to for example, to increase the temperature control and energy efficiency of the process. The length of the reaction tube is to be understood as meaning the total distance traveled by the reaction mixture in the microwave field. The reaction tube is at least one, but preferably several, such as two, three, four, five, six, seven, eight or more in length

 Surrounded by microwave heaters. The microwave radiation preferably takes place via the tube jacket. In a further preferred embodiment, the microwave irradiation takes place by means of at least one antenna via the tube ends. The reaction tube is usually at the inlet with a metering pump and a pressure gauge and at the outlet with a pressure holding valve and a

Heat exchanger provided. Preferably, the reaction mixture is the

Reaction tube in liquid form with temperatures below 100 ° C as

for example, supplied between 10 ° C and 90 ° C. In a further preferred embodiment, a solution of the polymer and carboxylic acid or

 Carboxylic ester only shortly before entering the reaction tube, optionally mixed with the aid of suitable mixing elements such as static mixer and / or Archimedean screw and / or by flowing through a porous foam. In a further preferred embodiment, they are in the reaction tube by means of suitable mixing elements such

For example, static mixer and / or Archimedean screw and / or further homogenized by flowing through a porous foam.

By varying the tube cross-section, length of the irradiation zone,

Flow rate, geometry of the microwave radiator, the irradiated microwave power and the temperature reached thereby are the

Reaction conditions adjusted so that the maximum reaction temperature is reached as quickly as possible. In a preferred embodiment, the residence time at maximum temperature is chosen so short that as few side or subsequent reactions occur as possible.

The continuous microwave reactor is preferably operated in monomode or quasi-monomode. The residence time of the reaction mixture in the irradiation zone is generally less than 20 minutes, preferably between 0.01 seconds and 10 minutes, preferably between 0.1 seconds and 5 minutes as

for example, between one second and 3 minutes. The reaction mixture can flow through the irradiation zone several times to complete the reaction, optionally after intermediate cooling.

In a particularly preferred embodiment, the irradiation of the reaction material with microwaves is carried out in a reaction tube whose longitudinal axis is in the direction of propagation of the microwaves in a monomode microwave applicator. Preferably, the length of the

 Irradiation zone at least half the wavelength, more preferably at least one and up to 20 times, especially 2 to 5 times, such as 3 to 0 times the wavelength of the used

Microwave radiation. With this geometry, energy from several, such as two, three, four, five, six or more consecutive maxima of the propagating parallel to the longitudinal axis of the tube microwave can be transferred to the reaction mixture, which significantly improves the energy efficiency of the process. The irradiation of the reaction product with microwaves preferably takes place in a substantially microwave-transparent straight reaction tube, which is located within a hollow conductor connected to a microwave generator and functioning as a microwave applicator. Preferably, the reaction tube is aligned axially with a central axis of symmetry of this waveguide. The waveguide is preferably formed as a cavity resonator. Preferably, the length of the

 Cavity resonator dimensioned so that it forms a standing wave. Further preferred are those not absorbed in the waveguide

Microwaves reflected at its end. By molding the

Mikrowellenapplikators as a resonator of the reflection type, a local increase in the electric field strength are achieved with the same power supplied by the generator and increased energy utilization. The cavity resonator is preferably operated in the Eoi _n mode, where n stands for an integer and indicates the number of field maxima of the microwave along the central axis of symmetry of the resonator. In this operation, the electric field is in the direction of the central axis of symmetry of the

Cavity resonator directed. It has a maximum in the area of the central axis of symmetry and decreases to the lateral surface to the value zero. These

Field configuration is rotationally symmetrical about the central axis of symmetry. By using a cavity resonator having a length where n is an integer, the formation of a standing wave is enabled. Depending on the desired flow rate of the reaction mixture through the

 Reaction tube, the required temperature and the required residence time in the resonator, the length of the resonator is selected relative to the wavelength of the microwave radiation used. N is preferably an integer from 1 to 200, particularly preferably from 2 to 100, in particular from 3 to 50, especially from 4 to 20, for example three, four, five, six, seven, eight, nine or ten.

The eoin mode of the cavity resonator is also known in English as

TMoin mode (transversal magnetic), see, for example, K. Lange, K.H. Löcherer, Taschenbuch der Hochfrequenztechnik ", volume 2, page K21 ff.

The irradiation of the microwave energy into the waveguide acting as a microwave applicator can take place via suitably dimensioned holes or slots. In a specific embodiment of the method according to the invention, the irradiation of the reaction material with microwaves in a reaction tube, which is located in a waveguide with coaxial transition of the microwaves. For this method, particularly preferred microwave devices are from a cavity resonator, a coupling device for coupling a

Microwave field in the cavity resonator and constructed with one opening at two opposite end walls for passing the reaction tube through the resonator. The coupling of the microwaves in the

Cavity resonator is preferably via a coupling pin, in the

Cavity resonator protrudes. Preferably, the coupling pin is as a Forming coupling antenna, preferably formed metallic inner conductor tube. In a particularly preferred embodiment, this protrudes

Coupling pin through one of the frontal openings in the cavity resonator inside. Particularly preferably, the reaction tube connects to the

Inner conductor tube of the coaxial transition and in particular it is guided through the cavity into the cavity resonator. Preferably, the reaction tube is aligned axially with a central axis of symmetry of the cavity resonator, for which purpose the cavity resonator preferably each has a central opening on two opposite end walls for passing the reaction tube.

The feeding of the microwaves in the coupling pin or in as

Coupling antenna acting inner conductor tube can be done for example by means of a coaxial connecting cable. In a preferred embodiment, the microwave field is fed to the resonator via a waveguide, wherein the protruding from the cavity resonator end of the coupling pin in a

Opening, which is located in the wall of the waveguide, is guided into the waveguide and removes microwave energy from the waveguide and coupled into the resonator.

In a specific embodiment, the irradiation of the reaction material with microwaves is carried out in a microwave-transparent reaction tube which is axially symmetrical in an EOM circular waveguide with coaxial transition of the microwaves. In this case, the reaction tube is guided through the cavity of an inner conductor tube acting as a coupling antenna into the cavity resonator. In a further preferred embodiment, the irradiation of the salt with microwaves in a microwave transparent reaction tube which _n cavity resonator with the axial feed of the microwave is passed through a E ₀ i, whereby the length of the cavity resonator is dimensioned in such a way that n = 2 or more Form field maxima of the microwave. In a further preferred embodiment, the irradiation of the reaction mixture with microwaves in a microwave-transparent reaction tube, which passed through a Eoi _n- cavity resonator with axial feeding of the microwaves is, wherein the length of the cavity resonator is dimensioned so that forms a standing wave with n = 2 or more field maxima of the microwave. In a further preferred embodiment, the irradiation of the reaction material with microwaves in a microwave-transparent reaction tube, which is axially symmetrical in a circular cylindrical E ₀ i _n cavity resonator with coaxial transition of the microwaves, wherein the length of the

Cavity resonator is dimensioned so that form n = 2 or more field maxima of the microwave. In a further preferred embodiment, the irradiation of the reaction mixture with microwaves takes place in one

Microwave-transparent reaction tube, which is axially symmetrical in a circular cylindrical eoin cavity resonator with coaxial transition

Microwave is located, wherein the length of the cavity is dimensioned so that forms a standing wave with n = 2 or more field maxima of the microwave.

Particularly suitable for the process according to the invention

Eoi cavity resonators preferably have a diameter which corresponds to at least half the wavelength of the microwave radiation used.

Preferably, the diameter of the cavity resonator is the 1, 0- to

10 times, more preferably 1, 1 to 5 times and especially 2.1 to 2.6 times the half wavelength of the microwave radiation used.

Preferably, the E ₀ i cavity resonator has a round cross-section, which is also referred to as Eoi round waveguide. Particularly preferably it has a cylindrical shape and especially a circular cylindrical shape.

When the process according to the invention is carried out continuously, the reaction mixture is often not yet in chemical equilibrium when leaving the irradiation zone. In a preferred embodiment, therefore, after passing through the irradiation zone, the reaction mixture is transferred directly, that is to say without intermediate cooling, into an isothermal reaction zone in which it is kept at the reaction temperature for a certain time. Only after leaving the isothermal reaction zone, the reaction mixture is optionally relaxed and cooled. Under the direct transfer from the Irradiation zone in the isothermal reaction path is to be understood that between the irradiation zone and isothermal reaction path no active measures for supplying and in particular for dissipating heat are taken. Preferably, the temperature difference between leaving the

Irradiation zone to the entry into the isothermal reaction path less than ± 30 ° C, preferably less than ± 20 ° C, more preferably less than ± 10 ° C and especially less than ± 5 ° C. In a specific embodiment, the temperature of the reaction product when entering the isothermal reaction path corresponds to the temperature when leaving the irradiation zone. This embodiment allows rapid and targeted heating of the reaction mixture to the desired reaction temperature without partial overheating and then a residence at this reaction temperature for a defined period. In this embodiment, the reaction mixture is preferably cooled as quickly as possible directly after leaving the isothermal reaction zone to temperatures below 120 ° C, preferably below 100 ° C and especially below 60 ° C.

As an isothermal reaction path all chemically inert vessels come in

Consider that a lingering of the reaction mixture in the in the

Allow irradiation zone set temperature. Isothermal reaction zone is understood to mean that the temperature of the reaction mixture in the isothermal reaction zone is kept constant relative to the inlet temperature to ± 30 ° C., preferably to + 20 ° C., more preferably to ± 10 ° C. and in particular to ± 5 ° C. Thus, when leaving the isothermal reaction zone, the reaction mixture has a temperature which deviates at most ± 30 ° C., preferably ± 20 ° C., more preferably ± 10 ° C. and in particular ± 5 ° C. from the temperature on entry into the isothermal reaction zone.

In addition to continuously operated stirred tanks and tank cascades pipes are particularly suitable as an isothermal reaction path. These

Reaction paths may consist of various materials such as metals, ceramics, glass, quartz or plastics, provided that they are mechanically stable and chemically inert under the selected temperature and pressure conditions. Have proven particularly thermally isolated vessels. The residence time of the reaction mixture in the isothermal reaction zone can be determined, for example, by the volume of the isothermal reaction mixture

Reaction distance are set. When using stirred containers and container cascades, it has proven equally appropriate to adjust the residence time on the degree of filling of the container. In a preferred embodiment, the isothermal reaction zone is with active or passive mixing elements

equipped.

In a preferred embodiment, a tube is used as the isothermal reaction section. This may be an extension of the

Microwave-transparent reaction tube after the irradiation zone or even a separate, related to the reaction tube tube of the same or different material act. Over the length of the tube and / or its cross-section can be at a given flow rate, the

Determine the residence time of the reaction mixture. The tube acting as an isothermal reaction section is thermally insulated in the simplest case, so that the temperature prevailing when the reaction mixture enters the isothermal reaction section is kept within the limits given above. The reaction mixture can in the isothermal reaction zone but also for example by means of a

Heat transfer medium or cooling medium targeted energy to be added or removed.

This embodiment has proven particularly suitable for starting the device or the method. Thus, the isothermal reaction path can be configured, for example, as a tube coil or as a tube bundle, which is located in a heating or cooling bath or acted upon in the form of a jacketed tube with a heating or cooling medium. The isothermal reaction zone can also be located in a further microwave applicator in which the reaction mixture is again treated with microwaves. Both single-mode and multi-mode applicators can be used. The residence time of the reaction mixture in the isothermal reaction zone is preferably selected such that the thermal equilibrium state defined by the prevailing conditions is achieved. Usually that is

Dwell time between 1 second and 10 hours, preferably between 10 seconds and 2 hours, more preferably between 20 seconds and 60 minutes, such as between 30 seconds and 30 minutes. Further preferably, the ratio between residence time of the reaction mixture in the isothermal reaction zone to the residence time in the irradiation zone between 1: 2 and 100: 1, more preferably 1: 1 to 50: 1 and in particular between 1: 1, 5 and 10: 1.

In order to achieve particularly high degrees of conversion, it has proven useful in many cases to suspend the reaction product obtained again from microwave irradiation, it being possible for the ratio of the reactants used to be supplemented by consumed or deficient starting materials.

The process according to the invention enables the polymer-analogous modification of hydroxyl-bearing polymers and in particular of polyvinyl alcohol with carboxylic acids or carboxylic acid esters in continuous as well

discontinuous process and thus in technically interesting quantities. In addition to water or lower alcohol there are no by-products to be disposed of and polluting the environment. A further advantage of the method according to the invention lies in the surprising observation that the polymer-analogous condensation reactions can be carried out in aqueous solution, since water is the solvent which is most suitable for hydroxyl-bearing polymers and is also advantageous from an ecological point of view. The addition of certain polar organic solvents can counteract an increase in viscosity which optionally occurs in the course of the process and facilitates the reaction with less water-soluble carboxylic acids or their esters. In particular, the process according to the invention is suitable for partial esterifications of polymers carrying hydroxyl groups, since the reaction mixtures, despite viscosity and solubility differences between hydroxyl-carrying polymers A) and carboxylic acids B1) and

Carboxylic esters B2) lead to a homogeneous distribution of carboxylic acid residues over the entire chain length of the polymer. The process according to the invention permits reproducible production along its chain length of statistically modified products. The variety of for the inventive Processes in commercial quantities of available carboxylic acids and carboxylic esters opens up a wide range of modification possibilities. By means of a suitable choice of the carboxylic acid, the swelling behavior, the solubility in water or organic solvents, the adhesion to differently polar substrates, the mechanical strength and the thermal stability of the polymers can be specifically modified by the process according to the invention. For example, by reaction with aliphatic

Hydrocarbon radicals carrying carboxylic acids B1) or carboxylic acid esters B2), the water solubility and hygroscopicity of the polymers reduced while improving the mechanical properties, in particular an internal plasticization. The polymers modified by the process according to the invention are versatile in use, for example as

Fibers, adhesives, emulsifiers, lamination for safety glass and plastics, paper coating, thickeners for latices, binders for fertilizers, water-soluble as well as water-insoluble films such as self-dissolving packaging films, as an additive to inks and concrete as well as a temporary, water-removable surface protection.

Examples

The discontinuous microwave irradiation was performed in a single-mode microwave reactor "initiator ^®" by the company Biotage at a frequency of 2.45 GHz. The temperature was measured with an IR sensor. As

Reaction vessels were closed, pressure-resistant glass cuvettes (pressure vials) with a volume of 20 ml, in which was homogenized with magnetic stirring.

The microwave power was adjusted over the experimental period in each case in such a way that the desired temperature of the reaction mixture was reached as quickly as possible and then kept constant over the period specified in the experiment descriptions. After completion of the

Microwave irradiation, the glass cuvette was cooled with compressed air. Continuous irradiation of the reaction mixtures with microwaves was carried out in a reaction tube (60 × 1 cm) made of aluminum oxide, which was axially symmetric in a cylindrical cavity resonator (60 × 10 cm). At one of the end faces of the cavity resonator, the reaction tube passed through the

Cavity of a functioning as a coupling antenna inner conductor tube. The microwave field generated by a magnetron with a frequency of 2.45 GHz was coupled by means of the coupling antenna into the cavity resonator (Eo-i cavity applicator, monomode) in which a standing wave

trained. When an isothermal reaction section was used, the heated reaction mixtures were conveyed immediately after leaving the reaction tube through a thermally insulated stainless steel tube (3.0 m × 1 cm, unless stated otherwise). After leaving the reaction tube or when using the isothermal reaction path after leaving the same were the

Reaction mixtures relaxed to atmospheric pressure, immediately by means of a

Intensive heat exchanger cooled to the specified temperature.

The microwave power was adjusted over the duration of the experiment in each case in such a way that the desired temperature of the reaction mixture was kept constant at the end of the irradiation zone. The microwave powers mentioned in the test descriptions therefore represent the time average of the irradiated microwave power. The temperature measurement of the

Reaction mixture was made directly after leaving the irradiation zone by means of Pt100 temperature sensor. Microwave energy not directly absorbed by the reaction mixture was reflected at the end face of the cavity resonator opposite the coupling antenna; the ones from

 Reaction mixture also not absorbed in the return and mirrored back in the direction of the magnetron microwave energy was using a

Prism system (circulator) passed into a water-containing vessel. From the difference between incident energy and heating of this water load, the microwave energy recorded in the irradiation zone was calculated

By means of a high-pressure pump and a pressure relief valve, the reaction mixture was placed in the reaction tube under such a working pressure, which was sufficient to keep all starting materials and products or condensation products always in the liquid state. The reaction mixtures were pumped through the device at a constant flow rate and the residence time in the reaction tube was adjusted by modifying the flow rate.

The analysis of the reaction products was carried out by means of ¹ H-NMR spectroscopy at 500 MHz in CDCl ₃ .

The solubility of the polymers was determined on films prepared as follows: 100 ml of a 6% by weight polymer solution dyed with Patent Blue V (6% strength by weight in terms of solids content) were poured onto a commercially available film casting plate and the Solution for 2 - 3 days in air

Room temperature dried. From this polymer film, an approximately 2 x 2 cm piece was cut out and clamped in a frame. The frame was placed in the solvent to be tested at the temperature to be tested

 (For example, water at 20 ° C) hung and measured with slow stirring the time to complete dissolution of the film. If the film was not completely dissolved after 600 seconds (= 10 minutes), it was termed "insoluble." Films of the polyvinyl alcohols used are not soluble under these conditions.

Example 1: Esterification of poly (vinyl alcohol) with coconut fatty acid 15 ml of a mixture of 3 g of polyvinyl alcohol (Mowiol ^® 4-98, molecular weight 27,000 g / mol; degree of hydrolysis 98%) in 8 g of water and 6 g of dimethylformamide (DMF), 30 mg p-toluenesulfonic acid and 2.3 g of coconut fatty acid (molecular weight

230 g / mol) were heated in the batch microwave reactor to a temperature of 190 ° C, wherein a pressure of about 18 bar was established. To

Achieving the thermal equilibrium (after about 1 minute) was maintained at this temperature and pressure for 10 minutes under further microwave irradiation. After completion of the microwave irradiation, the Reaction mixture cooled to room temperature and the catalyst with

Hydrogen carbonate solution neutralized.

The reaction product was a homogeneous, colorless solution with lower

Viscosity. After evaporation of the solvent and reprecipitation of the residue with methanol resulted in a viscous mass whose IR spectrum for esters of

Polyvinyl alcohol shows characteristic bands at 1735 cm ^"1 and 1245 cm ^{" 1} with a relation to the polyvinyl alcohol significantly increased intensity. The ¹ H-NMR spectrum shows at 2.3 ppm for a methylene group in α-position to an ester carboxyl group (-O-CO-CH ^ -) characteristic signal, which compared to the monomeric Cocosfettsäure a clear, for polymeric structures usual, broadening shows. By integration of this signal and comparison with the signals of the methine protons of the polymer backbone between 3.5 and 4.3 ppm, a degree of esterification of about 10 mol% of the

Hydroxyl groups of the polymer determined, which corresponds to a conversion of 65 mol% of the coconut fatty acid used.

A film cast from aqueous solution of this polymer showed a significantly increased flexibility compared to the starting material.

Example 2: Esterification of poly (vinyl alcohol) with succinic acid

10 ml of a mixture of 4 g of polyvinyl alcohol (Mowiol ^® 4-88, molecular weight 31,000 g / mol; degree of hydrolysis 88%) in 6 g water and 4 g of isopropanol, 50 mg of p-toluenesulfonic acid and 0.4 g of succinic acid were tested in the discontinuous microwave reactor heated to a temperature of 192 ° C, wherein a pressure of about 20 bar was established. After reaching the thermal equilibrium (after about 1 minute) was held for 15 minutes under further microwave irradiation at this temperature and pressure. After completion of the

Microwave irradiation, the reaction mixture was cooled to room temperature and the catalyst was neutralized with bicarbonate solution. The reaction product was a homogeneous, colorless, viscous, opalescent solution. After evaporation of the solvent resulted in a homogeneous, non-sticky film whose IR spectrum for esters of polyvinyl alcohol

shows characteristic bands at 1735 cm ^"1 and 1245 cm ^{" 1} with an increased intensity compared to the polyvinyl alcohol used. Attempts to dissolve the dried reaction product in DMF or DMSO failed, indicating the expected crosslinking of the polyvinyl alcohol. Only a swelling to about twice the mass of the polymer used could be observed after a few hours.

Example 3: Continuous esterification of poly (vinyl alcohol) with propionic acid

In a 10 l Büchi stirred autoclave with gas inlet tube, stirrer,

Indoor thermometer and pressure equalization became a solution of 2 kg

Polyvinyl alcohol (Mowiol ^® 4-98, molecular weight 27,000 g / mol, degree of hydrolysis 98%) in 5 kg of water, treated with 30 g of p-toluenesulfonic acid and heated to 55 ° C. At this temperature, a solution of 0.9 kg of propionic acid (12.3 mol) in 1, 1 kg of isopropanol was added over a period of one hour with stirring.

The resulting reaction mixture was pumped continuously at 5.0 l / h through the reaction tube at a working pressure of 35 bar and a

Microwave power of 2.1 kW exposed, of which 92% were absorbed by the reaction. The residence time of the reaction mixture in the

Irradiation zone was about 48 seconds. When leaving the irradiation zone, the reaction mixture had a temperature of 202 ° C and was transferred directly at this temperature in the isothermal reaction zone. At the end of the isothermal reaction zone, the reaction mixture had a temperature of 186 ° C. The reaction mixture was cooled to room temperature immediately after leaving the reaction section and adjusted to pH 4 with bicarbonate solution. The reaction product was a homogeneous, colorless solution with lower

Viscosity. Evaporation of the solvent in vacuo resulted in a viscous mass. The ¹ H-NMR spectrum shows at a chemical shift of 2.6 ppm newly added signals of the -Chb group as broadened

Multiplet. By comparing the integral of this signal with that of

 Methylene protons of the polymer backbone at 1, 5-1, 8 ppm, a conversion of 19 mol% of the polymeric hydroxyl groups was determined to Propionsäureester. This corresponds to a conversion based on the propionic acid used of 71 mol% of theory.

An aqueous solution cast film of the modified polymer completely dissolved in cold water within 410 seconds. In the DSC diagram, virtually no typical poly (vinyl alcohol) endothermic melting signal in the range around 200 ° C can be seen. This indicates a greatly reduced crystallinity of the modified polymer.

Example 4: Esterification of poly (vinyl alcohol) with coconut fatty acid methyl ester 10 ml of a mixture of 2 g polyvinyl alcohol (Mowiol 4-98, molecular weight 27,000 g / mol, degree of hydrolysis 98%) in 8 g water and 6 g dimethylformamide (DMF), 45 mg p Toluenesulfonic acid and 2.4 g Cocosfettsäuremethylester

(0.01 mol) were heated in a batch microwave reactor to a temperature of 190 ° C, wherein a pressure of about 18 bar was established. To

Achieving the thermal equilibrium (after about 1 minute) was maintained at this temperature and pressure for fifteen minutes with further microwave irradiation. After completion of the microwave irradiation, the reaction mixture was cooled to room temperature and the catalyst with

Hydrogen carbonate solution neutralized.

The reaction product was a homogeneous, colorless solution with lower

Viscosity. After evaporation of the solvent resulted in a viscous mass. The proton resonance spectrum shows, as already described in Example 1, the signal the methylene group adjacent to the ester grouping at 2.3 ppm. By integration of this signal and comparison with that of the methine protons of the

Polymer backbone between 3.5 and 4.3 ppm results in a degree of modification of 16 mol% of the hydroxyl groups of the poly (vinyl alcohol), which corresponds to a conversion of 72 mol% of Cocosfettsäuremethylesters used.

A film cast from aqueous solution of this polymer in turn showed a significantly increased flexibility compared to the starting material.

Example 5: Continuous esterification of poly (vinyl alcohol) with benzoic acid

In a 10 l Büchi stirred autoclave with gas inlet tube, stirrer,

Internal thermometer and pressure compensation became a solution of 1, 5 kg

Polyvinyl alcohol (Mowiol ^® 8-88, molecular weight 67,000 g / mol, degree of hydrolysis 88%) in 6 kg of water, treated with 30 g of p-toluenesulfonic acid and heated to 55 ° C. At this temperature, a solution of 530 g of benzoic acid in 1, 0 kg of isopropanol was added over a period of one hour with stirring.

The reaction mixture thus obtained was continuously pumped at a working pressure of 35 bar at 4.8 l / h through the reaction tube and a

Subjected to microwave power of 2.3 kW, of which 90% were absorbed by the reaction mixture. The residence time of the reaction mixture in the

Irradiation zone was about 50 seconds. When leaving the irradiation zone, the reaction mixture had a temperature of 198 ° C and was transferred directly at this temperature in the isothermal reaction zone. At the end of the isothermal reaction zone, the reaction mixture had a temperature of 180.degree. The reaction mixture was cooled to room temperature immediately after leaving the reaction section and adjusted to pH 4 with bicarbonate solution. The reaction product was a homogeneous, colorless solution with lower

Viscosity. After evaporation of the solvent and reprecipitation of the residue from ethanol resulted in a viscous mass whose IR spectrum for esters of

Polyvinyl alcohol shows characteristic bands at 1735 cm ^"1 and 1245 cm ^{" 1} with an increased relative to the polyvinyl alcohol used. The

¹ H NMR spectrum shows broad signals at chemical shifts of 7.5 and 8.0 ppm that are consistent with a polymer-bound benzoic acid ester. By comparing the integral of the signal at 8.0 ppm with that of the polymer backbone methylene protons at 1.5-1.8 ppm, a conversion of 11 mole percent of the polymeric hydroxyl groups was determined. This corresponds to one

Sales based on the benzoic acid used of 75 mol% of theory.

Example 6: Continuous esterification of poly (vinyl alcohol) with

m-sulphobenzoic acid, Na salt

In a 10 l Büchi stirred autoclave with gas inlet tube, stirrer,

Internal thermometer and pressure compensation became a solution of 1, 5 kg

Polyvinyl alcohol (Mowiol ^® 8-88, molecular weight 67,000 g / mol, degree of hydrolysis 88%) in 6 kg of water, with 30 g of sulfuric acid (97%) and heated to 55 ° C. At this temperature, over a period of one hour with stirring, a solution of 500 g of m-sulfobenzoic acid, Na salt in a mixture of 0.5 kg of isopropanol and 0.5 kg of water was added. The resulting reaction mixture was pumped continuously at 8 l / h through the reaction tube at a working pressure of 35 bar and a

Microwave power of 3.0 kW exposed, of which 95% were absorbed by the reaction mixture. The residence time of the reaction mixture in the

Irradiation zone was about 25 seconds. When leaving the irradiation zone, the reaction mixture had a temperature of 180 ° C and was transferred directly at this temperature in the isothermal reaction zone. At the end of the isothermal reaction zone, the reaction mixture had a temperature of 170.degree. The reaction mixture was immediately after leaving the reaction zone cooled to room temperature and adjusted to pH 4 with bicarbonate solution.

The reaction product was a homogeneous, colorless solution with lower

Viscosity. After evaporation of the solvent and reprecipitation of the residue from ethanol resulted in a viscous mass whose IR spectrum for esters of

Polyvinyl alcohol shows characteristic bands at 1735 cm ^"1 and 1245 cm ^{" 1} with an increased relative to the polyvinyl alcohol used.

Claims

claims:

1. Process for reacting hydroxyl-bearing polymers

Repeating structural units of the general formula (I)

in which

 D for a direct bond between polymer backbone and hydroxyl group, a Ci to Ce alkylene group, a C5 to Ci2-arylene group, a

Oxyalkylene group of the formula -OR ² -, an ester group of the formula -C (O) -O-R ² - or an amide group of the formula -C (O) -N (R ⁸ ) R ² -,

R ^{2 is} a C ² -C 10 -alkylene radical,

R ^{8 is} hydrogen or an optionally substituted C2 to

 Cio-alkyl radical and

n is a number between 3 and 5,000, with carboxylic acids B1) of the formula (II) or carboxylic esters B2) of the formula (III) R ¹ -COOH (II) R -COOR ⁷ (III) in which

R ^{1 is} a hydrocarbon radical having 2 to 50 carbon atoms, and

R ^{7 is} a C ₁ -C ₄ -alkyl radical in which hydroxyl-carrying polymers A) in the presence of carboxylic acids of the formula (II) or carboxylic acid esters of the formula (III), and in the presence of water are irradiated with microwaves, wherein the reaction mixture is heated by the microwave irradiation to temperatures above 100 ° C.

2. The method of claim 1, wherein the polymer in addition to the structural units of the formula (I) additionally comprises structural units derived from further ethylenically unsaturated monomers.

3. The method according to claim 1 and / or 2, wherein the structural units of formula (I) derived from vinyl alcohol.

4. The method according to one or more of claims 1 to 3, wherein the polymer in addition to the structural units of the formula (I) also comprises vinyl acetate derived structural units.

5. Method according to one or more of claims 1 to 4, wherein R ^{1 is} an alkyl radical

6. Method according to one or more of claims 1 to 5, wherein the carboxylic acid B1) or the carboxylic acid ester B2) is a mixture of at least one carboxylic acid and at least one dicarboxylic acid or a mixture of at least one carboxylic acid ester and at least one dicarboxylic acid ester.

7. The method according to one or more of claims 1 to 6, wherein the reaction mixture used for reaction contains 5 to 98 wt .-% water.

8. The method according to one or more of claims 1 to 6, wherein the reaction mixture used for reaction contains 5 to 98 wt .-% of a mixture of water and one or more water-miscible organic solvents.

9. The method of claim 8, wherein the proportion of the water-miscible organic solvent in the solvent mixture is between 1 and 75 wt .-%.

10. The method according to one or more of claims 1 to 9, wherein the reaction mixture is heated by means of microwave radiation to temperatures above 100 ° C.

11. The method according to one or more of claims 1 to 10, in which ester-carrying comonomer units of the polymer A) with carboxylic acids B1) or carboxylic acid esters B2) are transesterified.

12. The method according to one or more of claims 1 to 11, wherein the microwave irradiation takes place in a flow tube of microwave-transparent, refractory material.

13. The method according to one or more of claims 1 to 12, wherein the longitudinal axis of the reaction tube is in the propagation direction of the microwaves in a single-mode microwave applicator.

14. The method according to one or more of claims 1 to 13, wherein the microwave applicator is formed as a cavity resonator.

15. esters of hydroxyl-bearing polymers prepared by reacting hydroxyl-bearing polymers A), the repeating structural units of the general formula (I)

in which

D for a direct bond between the polymer backbone and the hydroxyl group, a C ₁ - to C ₆ -alkylene group, a C ₅ - to C ₂ -arylene group, a

Oxyalkylene group of the formula -OR ² -, an ester group of the formula

-C (O) -O-R ² - or an amide group of the formula -C (O) -N (R ⁸ ) R ² -,

R ^{2 is} a C ² -C 10 -alkylene radical, R is hydrogen or an optionally substituted C2 to

 Cio-alkyl radical and

n is a number between 3 and 5,000, with carboxylic acids B1) of the formula (II) or carboxylic esters B2) of the formula (III) R ¹ -COOH (II) R ¹ -COOR ⁷ (III) in which

R is a hydrocarbon radical having 2 to 50 carbon atoms, and

R ^{7 is} a C 1 -C ₄ -alkyl radical, wherein hydroxyl-carrying polymers A) in the presence of carboxylic acids of the formula (II) or carboxylic acid esters of the formula (III) and in the presence of water are irradiated with microwaves and wherein the reaction mixture by the microwave irradiation to temperatures is heated above 100 ° C.