DE2445959A1 - PROCESS FOR THE PREPARATION OF POLYMERS CONTAINING HYDROXYL GROUPS - Google Patents

Description

Our reference: 0.Z. 30 844 Ls / L 6700 Ludwigshafen, September 25, 1974

Process for the preparation of hydroxyl group-containing

Polymers

The present invention relates to a process for the preparation of polymeric substances containing hydroxyl groups, in particular the Production of polytetrahydrofuran with terminal hydroxyl groups from corresponding polymers containing acyloxy groups Substances through transesterification with alcohols.

Polytetrahydrofuran (PTHF) is usually produced from tetrahydrofuran using cationic catalyst systems, a polytetramethylene ether with different end groups determined by the initiator system is obtained. PTHP corresponds according to the general formula

X - / ÖE _o ) _k - 0_7 "- (CH _o ) h - Y,

where X and Y can stand, for example, for the following groupings and η denotes _{the valency of the Lewis acid MX n:}

Catalyst system X Y

R ₃ O ⁺ MX.

FSO ₃ H A1C1 ₃ / CH ₃ COC1

SbCl, - / (CH, CO-) O

^ l S

RO- -OH HSO ₃ -
CH ₃ COO-
CH ₃ COO- -F
-Cl
-0OCCH ₃ CH ₃ COO- -0OCCH ₃

The main area of application of PTHF, the polyurethane resin sector, he calls for polyethers in which the end groups X and Y are hydroxyl

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groups are. Therefore, the end groups in the polymer initially obtained must be converted into alcohol functions by suitable measures. The methods that have become known to date mostly use alkaline saponification with, for example, NaOH, Ca (OH) ₂ , Na ₂ CO, or NH ^ OH solutions. Such a process, which reflects the current state of the art, is described, for example, in US Pat. No. 3,358,042. Here the difficult process engineering problems which the saponification reaction of macromolecular substances brings with it are overcome in that it is carried out in special solvents. This in turn causes a component of the inefficiency for the process insofar as an additional solvent circuit has to be set up and a total of seven separate operational steps have to be carried out after the polymerization, as described in this US patent. In addition, the process is not very environmentally friendly because it is loaded with a considerable amount of salt and, depending on the molecular weight of the PTHP produced, 10 to 35 %, based on the polymer, salt load (NaP and Na ₂ SOh) must be eliminated.

The present invention was based on the object of providing a process that is simpler in terms of process technology and therefore more economical To develop more environmentally friendly process, which does not adhere to the disadvantages outlined above, and both for the production of PTHP with OH end groups as well as for the conversion of other polymers containing acyloxy groups into hydroxyl groups containing polymers is suitable.

It has now been found that acyloxy groups, preferably acetate groups containing polymers, can advantageously be converted into those with hydroxyl groups when they are in the presence of hydrohalic acids and water are subjected to a transesterification reaction with alcohols.

The present invention relates to a process for the production of polymeric substances containing hydroxyl groups from acyloxy groups polymeric substances by transesterification with alcohols, which is characterized in that the transesterification

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reaction in a mixture of water, at least one up to alcohol containing ten carbon atoms and hydrogen halide is carried out.

The process of the invention is for the conversion of polymers suitable, which carry organic ester groups, preferably an acetate radical.

Polymers which are suitable for the transesterification according to the invention are, in addition to the PTHP prepared in a known manner, in general those derived from homo- and copolymeric alcohols esterified with carboxylic acids. Such polymers are usually prepared by homo- or mixed polymerization from the corresponding monomers bearing ester groups, such as e.g. Isopropenyl, allyl or vinyl acetate, obtained e.g. by radical polymerization. Copolymers are also suitable these monomers are copolymerizable with other olefinically unsaturated monomers Compounds such as olefins, vinyl aromatics and / or vinyl halides, e.g., styrene, butadiene, ethylene and vinyl chloride for the transesterification reaction according to the invention.

The usual transesterification initiated by alkaline catalysts is less suitable for polymers containing aeyloxy groups, Because this often leads to the formation of emulsions that are difficult to break and have a strong tendency to foam, the catalysts difficult to separate and ultimately mostly discolored reaction products are formed. The well-known sour catalyzed transesterification, the presence of water is avoided. However, this procedure is not suitable for the implementation of the polymers described above. Will the reaction carried out with the exclusion of water, so in this case too polymeric alcohols are formed, which - although of colorless Esters are assumed - are strongly discolored. In addition, the products contain one more or less after the transesterification large number of double bonds in the molecule.

It was therefore surprising that the reaction in the presence of water led to colorless products which did not contain double bonds contain. In addition, it would have been expected that the

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Reaction in the presence of water would split off the ester group of the polymer as acids. But this is inexplicable not the case. Acids are formed - if at all - only to a very subordinate extent, although in comparison to the Ester groups in the polymer water is usually used in excess.

Unexpected was also the finding that according to the invention Embodiment the low-boiling distillates obtained in the transesterification do not discharge any hydrohalic acid. Is working if, however, in the absence of water, considerable amounts of catalyst are discharged with the distillate, which supplements which is a cost and environmental problem.

The method according to the invention thus has a number of unforeseeable advantages over the prior art.

The amount of water to be used for the process according to the invention is generally between 5 and 50, preferably between 10 and 1 % by weight, based on the alcohol used.

Alcohols with up to 10 carbon atoms suitable for transesterification are the customary straight-chain or branched alcohols, preferably monofunctional primary and secondary alcohols with a carbon number of less than 10. Alcohols with J> to 5 carbon atoms, such as n- Propanol, isopropanol, n-butanol-1, n-butanol-2, isobutanol and 3> -methylbutanol-1. However, methanol and ethanol can also be used with success.

There is no upper limit to the amount of alcohol required for the transesterification according to the invention. Down you will be in the generally choose a 5 to 20-fold molar excess, based on the ester equivalents, in the polymer. Basically however, larger or smaller quantities can be used.

The hydrohalic acid used as a catalyst can Be fluoric, chloric, bromic or hydriodic acid. From economic

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hydrochloric acid is preferred for economic reasons. The catalyst concentration is not critical. Although it influences the transesterification rate, it is already sufficiently large at 0.1 to percent by weight acid, based on the polymer, if reaction ^{temperatures above 50 °} C. are chosen »

The transesterification is carried out in accordance with the customary ones Procedure in which the lower-boiling ester formed or its azeotrope with alcohol and water is by distillation is removed from the reaction mixture. Dragged along After the phase separation, water can be returned to the reaction.

Since the procedure under normal pressure is preferred for economic reasons, the reaction temperature is determined by the boiling point of the alcohol-water mixture. In the above-mentioned preferred alcohols it is therefore suitably about lie between 80 and 120 ⁰ C. If very high-boiling alcohols are used, the use of negative pressure can be recommended if the substrate to be converted is thermally unstable.

The proportion of polymer in the reaction mixture can be proportionate vary widely, in general it is between 10 and 90, preferably between 50 and 80 percent by weight.

The transesterification can be carried out continuously or batchwise will. You have to do that with both embodiments replenish the water discharged from the distilled overhead product in the sump again. Will be the lower boiling point during transesterification If the product is subjected to fractional distillation, a top product is obtained which contains more esters than one, obtained without rectification. In the latter case, the reaction mixture is depleted in alcohol. However, it will be a from the start If a sufficiently large excess of alcohol is used, it is not necessary to replace it in the reaction mixture. That with the transesterification The catalyst-free distillate obtained can be separated into the Components alcohol, ester and water are broken down.

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The separation of excess alcohol and water from the polymer happens according to well-known separation processes. For example, you can first use the catalyst with alkali neutralize, remove water by azeotropic distillation, filter off the precipitated salts and evaporate the alcohol. But you can also do without the neutralization and the hydrogen halide Remove acid by distillation with the alcohol «This works best if water is removed from the reaction mixture beforehand has been completely removed.

The process products prepared according to the invention are suitable, for example, as polyfunctional alcohols for the preparation of polyurethane resins. They are characterized, among other things, by their resistance to hydrolysis.

The parts or percentages mentioned in the following examples are parts by weight or percentages by weight. Behave parts of the room to parts by weight like liters to kilograms.

example 1

A mixture of 900 parts of an ethylene-vinyl acetate copolymer with a molecular weight of about 2,000 and a vinyl acetate content of about 30 %, 740 parts of n-but of oil-1, 144 parts of water and 14 parts of concentrated hydrochloric acid are added with stirring to Boiling heated. The boiling temperature is 98 ^° C. Over the course of 5 hours, 1,600 parts of organic phase are distilled off without fractionation; the same amount of water-saturated n-butanol-1, l40 parts of water and the aqueous phase distilled off are fed to the reaction mixture in the same period of time. The organic phase distilled off consists of butanol, butyl acetate and water. It is halogen-free and only contains traces of acetic acid. After 5 hours, the distillation is continued without recirculation of the aqueous phase. As soon as the water has been completely removed and the boiling point of the butanol has been reached, the distillate removes the hydrochloric acid used as a catalyst from the reaction product. The neutral polymer solution is then freed from butanol in vacuo. The remaining polymeric alcohol has a hydroxyl number of 163 mg KOH / g and a saponification number of> 2 mg KOH / g.

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Polymers with hydroxyl numbers of 169 or 168 mg KOH / g are obtained if you proceed as described, but n-butanol-1 is replaced by isobutanol or 3-methylbutanol-1.

Example 2

703 parts of polytetrahydrofuran with a molecular weight of 76O and a saponification number 148, the molecular ends of which carry acetyl groups, are mixed with 50.5 parts of n-butanol-1, 100 parts of water and 5 parts of concentrated hydrochloric acid. The mixture is heated to boiling with stirring and 100 parts of organic phase per hour are taken off at the top of the column via a glass packed column (theoretical number of plates approx. 10) at a reflux ratio of 1: 1. The heavy aqueous phase appearing at the top of the column at the same time is returned to the still. The organic phase distilled off is replaced by water-saturated butanol. The distillate boiling at first obtained 9I ⁰ C. It contains in addition to water and butanol 30% butyl acetate. Acetic acid and chlorine cannot be detected in it. The head temperature rises in the course of the distillation. It reached 95 ° C after 11 hours. Butyl acetate can no longer be detected in the distillate. The theoretically expected amount of butyl acetate can be detected in the total amount of distillate.

The mixture is then neutralized by adding 7 parts of soda and water in the batch is removed from the system by azeotropic distillation with butanol. The remaining Polytetrahydrofuranlösung is freed by filtration from salt residues and in the film evaporator evaporated (120 ⁰ C to 1 Torr). A polymer having a hydroxyl number of 147.5 mg KOH / g, a saponification number of 0.3 mg KOH / g and a hydrogenation iodine number <1 is obtained.

The same result is obtained when hydrochloric acid is replaced by the equivalent Amount of hydrobromic acid is replaced.

Example 3

500 parts of polytetrahydrofuran with a molecular weight of 2,000 (saponification number 56 mg KOH / g), the molecular ends of which are acetyl groups • wear, with 64 parts of methanol, Ij5 parts of water and 6

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Parts of concentrated hydrochloric acid mixed and reacted as described in Example 2. The distillate obtained first initially boils at 56 ^° C. and contains methyl acetate and methanol. The same amount of methanol is added to the sump as the distillate is withdrawn. »Approximately J> 0 parts of distillate are withdrawn every hour. After 8 hours the boiling point has risen to 65 ° C. and the transesterification is complete. For neutralization, the bottom product is ^{stirred with β parts of soda at 70 °} C. for 2 hours and then filtered. The polytetrahydrofuran solution is freed from methanol in a film evaporator. A polymer is obtained with a hydroxyl number of 55 mg KOH / g and a saponification number 0.6 mg KOH / g.

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Claims (1)

ο.ζ. 50 844 Claim Process for the preparation of hydroxyl-containing polymeric substances from acyloxy-containing polymeric substances by transesterification with alcohols, characterized in that the transesterification reaction is carried out in a mixture of water, at least one alcohol containing up to ten carbon atoms and hydrogen halide. BASF Aktiengesellschaft 609816/0853