WO2006097656A1

WO2006097656A1 - Synthesis of polylactone-grafted evoh

Info

Publication number: WO2006097656A1
Application number: PCT/FR2006/050217
Authority: WO
Inventors: Amar Zerroukhi; Frédéric BECQUART
Original assignee: Universite Jean Monnet; Centre National De La Recherche Scientifique
Priority date: 2005-03-15
Filing date: 2006-03-13
Publication date: 2006-09-21
Also published as: FR2883290A1

Abstract

The invention relates to a method for the synthesis of polylactone-grafted EVOH, comprising the following steps consisting in: producing a solvent-free homogeneous mixture containing at least EVOH, at least one monomer comprising a lactone ring and at least one catalyst or initiator; and stopping the polymerisation reaction after a few minutes.

Description

EVOH-GRAFFE-POLYLACTONE SYNTHESIS

The present invention relates to a polymer-graft-polylactone synthesis process characterized by a reduced reaction time. It also relates to the polymers thus obtained, their use for direct applications in pure form or in mixture, as well as for their reaction with other polymeric materials or organic molecules.

Polymer graft-polylactone synthesis is based on the chemical modification of hydroxylated polymers, by lactone ring opening polymerization (cyclic ester structure), initiated on the hydroxy functions of the polymer.

The polymerization of lactone monomer, co-initiated by an organometallic initiator such as tin bis (2-ethylhexanoate) or aluminum isopropoxide, in the presence of molecules or macromolecules carrying a hydroxy function, is not new. This mode of synthesis, in the presence of alcohol functions as a co-initiator, has been studied over the past fifteen years by authors referring to the subject [I].

The advantage of using a molecule or macromolecule bearing a hydroxyl function as a co-initiator is twofold when it is desired to polymerize lactone by means of an initiator of organometallic type, such as, for example, aluminum alkoxides, alkoxides of titanium, alkoxides or carboxylates of tin. On the one hand, this greatly reduces reaction times. On the other hand, it is possible to functionalize a polylactone chain end with the constituent unit carrying the hydroxy function. If the constituent unit has more than one hydroxy function, then all hydroxy functions can potentially initiate lactone polymerization. The fact that a hydroxyl function initiates or not a polymerization depends on various criteria: chemical environment of the carbon bearing the hydroxy function (tacticity or carbon configuration), variable for the different hydroxyl functions likely to react; effectiveness of the initiator used, which will depend on its chemical structure and logically the amount used.

In the current state of the art, most of the polymerization reactions of lactones, or even lactides, co-initiated with an alcohol are in solution, by means of a solvent. Indeed, the use of initiator as those mentioned in document [1], in the presence of solvent, would allow better control of the polymerization reactions at temperatures below 130 ° C. Under these conditions, the reaction times announced are several hours.

Very little work reports on the use of synthetic hydroxylated polymers to start one or more lactone monomer polymerization reactions. However, one can quote works dating from the years 2001-2002, where EVOH [2,3] and PVA [4] are modified in the presence of solvent.

Prior US Pat. No. 5,321,088 presents for the first time the possibility of modifying a hydroxylated polymer, in this instance polyethylene bearing vinyl alcohol units, in other words EVOH, from its hydroxy functions, by ring opening polymerization. lactone. The reactions described are in solution in xylene, at 115 ° C., with stannous octoate as initiator. Biodegradability tests conducted over several weeks are conclusive.

Furthermore, US Pat. No. 5,612,412, US Pat. No. 5,922,808 and US Pat. No. 5,904,974 are in the form of melt synthesis by lactone ring opening polymerization, in which the hydroxy function is carried by PVA.

More particularly, US Pat. Nos. 5,922,808 and 5,904,974 describe reactions carried out in the molten state in a reactor, but for periods of at least 6 hours with a slow melt process. The implementation of a reactive extrusion process is mentioned, but the residence time in extruder a few minutes is totally incompatible with the reaction time of several hours.

US Pat. No. 5,612,412 also mentions reactions in the molten state by means of closed mixers, with reaction times ranging from 10 minutes to 5 hours for mass PV A / monomer ratios of less than 2. The initiator allows to obtain a total conversion of the monomer with reaction times of 10 min is monobutyl tris (2-ethylhexanate) tin. This initiator, of conventional chemical structure for this type of reaction, is however little used according to the literature. Moreover, the analysis of the examples reveals that all the reagents, including the initiator, are first mixed in heterogeneous phase, which excludes obtaining a final material derived from PVA, homogeneous.

EP-A-0 787 755 relates to the modification of EVOH with lactones in the molten state. It is systematically mentioned a slow transition from a heterogeneous state to a homogeneous and molten state, in a temperature range of around 180 ° C, with a maximum of 220 ° C. Moreover, and again, the reactions are carried out over several hours (6 hours in the examples cited) after the transition to the molten state. The only initiator illustrated in the examples is titanium tetrabutoxy. No chemical analysis to evaluate the structure of the final material (including homogeneity) and the amount of residual monomer is described. The inventors rely solely on solubility tests in epsilon-caprolactone to say that there has been grafting.

Document EP-A-0 339 472 describes a reaction process between a lactone and a hydroxylated polymer, in particular between PVA and epsilon caprolactone, carried out in the absence of a solvent, in the presence of a catalyst that is preferably of the type Lewis acid (in particular BF3), at a temperature of between 100 and 300 ^° C. and for a duration of between 1 minute and 6 hours. The final product obtained, although not characterized can be used in particular as an adhesive. If this last document addresses one of the problems of the invention, namely a very short reaction time, the process described is certainly illustrated for PVA but not for EVOH. However EVOH differs from PVA, both by a much smaller number of reactive hydroxyl groups (generally around 56% against 82% for PVA) and by a high hydrophobicity which makes the diffusion of lactones much more difficult.

All of this work, relating to the synthesis of polymer graft-polylactone, highlights the following technical problems: the use of solvents that are expensive and / or difficult to eliminate and / or harmful to the environment; long reaction times (greater than several hours); non-homogeneous reaction media resulting in heterogeneous final products.

The technical problem to be solved by the present application is therefore to provide a new method for synthesizing EVOH-graft-polylactone which does not have the disadvantages mentioned above.

This is achieved by the method according to the invention which comprises the following steps: a homogeneous, solvent-free mixture comprising at least EVOH, at least one monomer comprising a lactone ring and at least one catalyst or initiator is produced; the polymerization reaction is stopped after a period of less than one hour.

The polymerization reaction, by opening the lactone ring, involved in the present invention requires the presence of at least three reagents: The base polymer is a synthetic hydroxylated polymer, namely a hydroxy functional carrier and not identical to natural polymers of the starch or cellulose type. Such polymers carry vinyl alcohol units. It is more specifically EVOH (polyethylene-co-vinyl alcohol). Preferably, the EVOH used in the context of the invention comprises at least 1% (in proportion to the units) of vinyl alcohol unit.

The general structure of a hydroxylated polymer preferably used according to the invention is presented below:

x, y and z represent the molar percentages of the respective units, with: 0 <x ≤ 99; 0 <y <50; l <z <99; x + y + z = 100.

In the case of EVOH, y is preferably 0. For this type of hydroxylated polymers, the corresponding units are generally distributed in block sequence or randomly on the main chain, but not necessarily.

It should also be noted that EVOH, comprising a third constitutive unit in a proportion of less than or equal to 5% (in number of units), is also concerned by the invention.

At least one monomer having a lactone ring is also involved in the polymerization reaction. A mixture of different monomers can of course be used. These are cyclic monomers containing the ester function included in the ring. In the context of the invention, the following lactones may be used: beta-lactones, such as beta-propiolactone, dimethylpropiolactone and α, α-dimethyl-β-propiolactone; gamma-lactones, such as gamma-caprolactone; delta-lactones, such as delta-valerolactone, delta-caprolactone; epsilon-lactones, such as epsilon-caprolactones. Preferentially, delta-lactones and epsilon-caprolactones are used.

Among the delta-lactones, delta-valerolactones such as 5-valerolactone, 3-methyl-5-valerolactone, 3,3-dimethyl-5-valerolactone, 2-methyl-5-valerolactone and 3-ethyl 5-valerolactone are preferred.

Among epsilon-lactones, epsilon-caprolactones, such as epsilon-caprolactone, monoalkyl-epsilon-caprolactone such as monomethyl-epsilon-caprolactone or monoethyl-epsilon-caprolactone, are preferred.

In conclusion, the monomer thus comprises a lactone type ring of 4 to 10 units, (poly) substituted or unsubstituted. It should be noted that lactones with 5-atom rings, whose low reactivity is known, represents a disadvantageous solution in the context of the present invention.

In addition, the polymerization reaction takes place in the presence of at least one catalyst (regenerable) or an initiator (consumed in the reaction), which makes it possible to reduce the reaction times.

In the context of the invention, initiators or organometallic catalysts are preferred. More particularly, transition metals with alkoxy groups or transition metals with carboxylate groups are selected. In particular, mention is made of titanates, such as titanium tetrabutoxide, titanium tetrapropoxide or titanium tetraethoxide; tin, such as tin octanoate (or bis (2-ethylhexanoate) tin or tin octoate or stannous octanoate); the aluminum alkoxides, such as aluminum triisopropoxide. Rare earth catalysts can also be used.

Advantageously, the reaction mixture consists of 100 parts by weight of synthetic hydroxyl polymer containing n moles of hydroxy function, n / 100 to 100 n moles of monomer and n / 1000 to n / 5 moles of catalyst or initiator.

The reaction mixture is further characterized in that it is free of solvent. Economically, the absence of any solvent saves the purchase. This also makes it possible to do without any post-synthesis processing necessary for its elimination and to reduce the synthesis times. Moreover, from an environmental point of view, it is very advantageous to carry out syntheses without solvent, since the solvents of EVOH (dimethyl sulfoxide, trichlorobenzene, etc.) are generally heavy and difficult to eliminate or even toxic.

An essential characteristic of the process according to the invention is the production of a homogeneous mixture between the at least three reagents mentioned above. In practice and in the absence of any solvent, the homogeneity of the reactive system is ensured by carrying out the mixing either in the molten state or by dissolving the hydroxylated polymer in the monomer.

For melt modification, the monomer is introduced into the synthetic hydroxyl polymer in the molten state. In practice, the molten state is reached when the temperature is greater than or equal to the polymer melting point (in the case of semi-crystalline polymer) or the glass transition temperature of the polymer

(in case of amorphous polymer). It is necessary to rapidly melt the hydroxylated polymer before or simultaneously with the introduction of the monomer, to have a homogeneous mixture between the reactants. The same logic applies to the introduction of the initiator: it must be mixed intimately and quickly with monomer and the hydroxylated polymer before its reaction, otherwise the chemical modification of the hydroxylated polymer will necessarily be heterogeneous. This heterogeneity is manifested by the coexistence of strongly modified and weakly modified chains, linked to varying local concentrations of initiator and / or monomer.

The molten state also makes it possible to reduce the reaction times in the presence of an initiator.

The Applicant has also shown that it is possible to dissolve the hydroxylated polymer in the monomer. Indeed, under certain conditions, the monomer is capable of rapidly and completely diffusing into the hydroxylated polymer in the form of a powder or granule. In this case where the lactone monomer plays both the role of solvent and reagent, the process must be carried out at a temperature below the melting point of the hydroxylated polymer but higher than its glass transition temperature.

In practice and to cover these two cases of figures, the process according to the invention takes place at a temperature between -60 ° C and + 60 ° C of the melting temperature of the EVOH.

In addition and according to the invention, the polymerization reaction is stopped before one hour, preferably after a reaction time of between 1 and 30 minutes, advantageously less than or equal to 15 minutes, or even 10 or 5 minutes.

In both cases (melt or dissolution), the process according to the invention can be carried out either conventionally in a closed reactor with stirring, or continuously in an extruder.

The syntheses made in closed reactor with stirring are carried out for example by means of an anchor. The monomer is premixed with the polymer hydroxylated at a suitable temperature, generally between 130 and 250 ° C. The monomer may be preheated before the reaction temperature before its introduction and the hydroxylated polymer, previously heated to a temperature slightly lower than its melting temperature, also before its introduction. Once the system is melted or dissolved, the initiator, diluted or not in monomer, is added in order to reduce the reaction time.

For syntheses carried out by a continuous process such as extrusion, the hydroxylated polymer is introduced through the hopper. The monomer may be introduced either through the hopper together with the hydroxylated polymer, or by means of a pump into a specific zone. It is preferable to introduce the initiator either with the hydroxylated polymer, or diluted in the monomer, or specifically by means of a pump on a homogeneous polymer / monomer mixture already melted. For the latter case, it is necessary to inject the initiator by a third zone, the most downstream of the hopper.

The possibility of modifying the EVOH in the molten state, or even by reactive extrusion, appears to be particularly inventive. In fact, whether natural or synthetic, hydroxylated polymers have a reputation or are recognized as rapidly degrading above their melting temperature, that is to say generally above 200-240 ° C. In addition, the organometallic initiators used for the lactone ring opening polymerization of PVA or EVOH are used for the most part in solvents at temperatures below 130.degree. have chain lengths controlled and not to have reaction times reduced to a few minutes.

Furthermore, the reduction of these reaction times is all the more important as it makes it possible to minimize or even eliminate secondary reactions, for example transesterification and alcoholysis. These side reactions have never been taken into account in previous work. However, all Organometallic initiators used in this type of reaction are also known to be capable of generating such reactions at temperatures greater than or equal to 200 ° C. In addition, long reaction times, at such temperatures, are often the cause of degradations. thermal hydroxylated polymers. The Applicant has indeed shown that these side reactions were significant beyond one hour of reaction: while the monomer is consumed within a few minutes of reaction, it is observed, using a suitable initiator such as stannous octoate or aluminum isopropoxide, a continuous increase over the hours of the viscosity of the reaction system, a decreasing flexibility of the final material, and a solubility that decreases in many solvents such as alcohols (methanol, ethanol, ...) and DMSO. The development of these side reactions has been proven by the Applicant.

On the contrary, for reactions stopped after the monomer had been consumed (after a few minutes), no degradation phenomenon is observed.

The EVOH-graft-polylactone polymers obtainable by the claimed process are also part of the invention.

They are distinguished from those obtained by the processes of the prior art in several ways: due to the short reaction time, they have not (or less) undergone secondary reactions of transesterification or degradation type. Moreover, the homogeneity of the reaction system ensures the production of a homogeneous final material in terms of grafting. The general structure of the hydroxyl-graft-polylactone polymers preferentially obtained according to the invention is presented below:

x, y, z and t are mole percentages of the respective units, with: O <x <99; O <y <50; 1 <z <99, 1 <t <99; x + y + z + t = 100.

The corresponding patterns are usually distributed randomly on the main chain but not necessarily. R may be a hydrogen atom, an acetate group, or any group originating from the initiator or resulting from a chemical reaction with the hydroxyl function constituting a polylactone chain end. n is the average degree of polymerization of the lactone units introduced and n is in a range of 0.1 <n <100. a is a number characterizing the size of the lactone ring and is between 2 and 10. y is the number of units residual acetate. In general, the EVOHs result from a total hydrolysis of an EVAc (polyethylene-co-vinyl acetate). The presence of acetate unit is expected to decrease the transformation temperatures of the starting EVOH.

In the structure presented above, in the case of EVOH, y is preferentially = 0 and the lactone unit of epsilon-caprolactone (PCL).

The properties of the final material are multiple because they can be completely modulated by the formulation, in particular by the initial mass ratio between the hydroxylated polymer and the monomer. For small quantities of incorporated lactone, the final copolymer will have properties close to those of the polymer of initially, while for high amounts of lactone incorporated, the material may have properties close to the polylactone.

Thus, for intermediate ratios, the EVOH-g-PCL has completely original properties because the material no longer has any crystallinity and is purely amorphous. In addition, the mass ratio between the EVOH and the monomer will depend on the final properties of the material such as its flexibility and tackiness.

Moreover, the initiator used can make it possible to initiate the formation of a number of polylactone chains greater than the amount used. Transfer reactions can take place parallel to the main polymerization reaction. The average degree of polymerization, and therefore the degree of substitution of the hydroxy functions, is variable according to the amount of initiator used, its nature and the temperature.

Another aspect of the invention relates to a process for the preparation of EVOH-graft-polylactone derivatives according to the invention and the derivatives thus obtained.

In fact, the EVOH-graft-polylactone polymers according to the invention, for example EVOH-g-PCl, remain materials with hydroxyl functional groups capable of reacting. It is possible to mention the possible modification of the hydroxylated polymer by anhydrides, for example methacrylic anhydride, isocyanates, epoxies, for example glycidyl methacrylate, carboxylic acids, amines, etc. Any modification of this material, simultaneously with its synthesis or after its synthesis, can thus be envisaged. Due to the lowering of the melt conversion temperatures of these hydroxyl-graft-polylactone polymers, compared to the starting hydroxyl polymer (melting temperature if it remains and glass transition temperature decreased), new reactions can be considered with the EVOH-g-PCL in the molten state, for example to make them crosslinkable and to give them new applications. It is in particular possible to graft, in the molten state, unsaturations on EVOH-g-PCL at a lower temperature.

In addition, the EVOH-graft-polylactone polymers according to the invention are materials having ester functions. They can therefore be modified by transesterification reactions, with polymers also carrying ester functions. These transesterification reactions are likely to occur during the synthesis of the hydroxyl-grafted polylactone polymer, depending on the initiator used. Indeed, most of the initiators mentioned here are initiators also recognized for their greater or lesser efficiency in transesterification reactions. In the presence of partially hydrolyzed EVOH, i.e. with pendant acetate functions in their chains, the transesterification reactions are even more likely. Thus, in practice, it is possible to mix a graft-polymer-polylactone with a polymeric material having ester functions and to react together by transesterification reaction. The respective parts by weight of these polymers can be between 5 and 95%, 95 and 5%, respectively.

The new materials obtained in the context of the invention (EVOH-graft-polylactone polymers and their derivatives) have remarkable properties that can be used in various applications.

The EVOH-graft-polylactone polymers, in particular EVOH-g-PCL, are smokable materials and can therefore be used for the formation of films. Films of a few microns are achievable. At a low monomer level, the barrier properties of the hydroxylated synthetic polymer (EVOH) could be retained. The hydroxyl-graft-polylactone polymers (EVOH-g-PCL) are more adhesive on any type of support or materials than the hydroxylated polymer (EVOH) starting. We can therefore consider the formation of multilayer films. Applications in the field of food films can also be envisaged taking into account the announced properties of the filmability of the material. Furthermore, these materials can be used in the production of biofragmentable films, related to the recognized biodegradability of polylactones, especially polycaprolactone.

The EVOH-graft-polylactone polymers (EVOH-g-PCL) are more flexible than the hydroxylated polymers (EVOH) from which they are derived. As a result, they can serve as a softening agent, as an additive or substituent for the hydroxylated base polymer. This type of material thus makes it possible to avoid the use of plasticizers, often considered as pollutants.

EVOH-graft-polylactone polymers (EVOH-g-PCL) can also serve as a compatibilizing agent in polymer blends. In particular, it is possible to mix a polylactone grafted EVOH, an apolar or polar polymer material and a polar polymer material, with respective parts by weight of between 5 and 80%, 95 and 5% respectively and between 5 and 95%. In fact, the hydroxyl-graft-polylactone polymers, in particular EVOH-g-PCL, are copolymers having a large proportion of ethylenic apolar units and polar units of hydroxyl and ester. As a result, these copolymers can serve as a compatibilizing agent in polymer blends, especially polyolefin-type polymers or polymers which also contain the ester and hydroxy function.

Finally, the EVOH-graft-polylactone polymers (EVOH-g-PCL) can be formulated so as to have adhesive properties, particularly remarkable when hot.

EXAMPLES OF REALIZATION

The invention is illustrated with the aid of Examples 1 to 8 presented below, as well as of the appended figures 1 and 2. However, these examples have no limiting effect on the scope of the present invention. Figure 1 corresponds to the 250 MHz NMR spectrum of a sample synthesized in Example 2 (solvent: DMSO-d6).

Figure 2 corresponds to the 250 MHz NMR spectrum of a sample synthesized in Example 6 (solvent: DMSO-d6).

1 - Example 1

Epsilon-Caprolactone (CL) has been used for the modification of polyvinyl alcohol (PVA). The grafting of CL, by ring opening polymerization initiated on the hydroxy functions of PVA, was carried out in a molten state in a two-liter glass reactor. A steel anchor for stirring the reaction system is fixed on a steel stirring plateau. The reactor lid is equipped with four conical apertures to fix the stirring stage, a coolant, and a thermocouple. A stream of nitrogen is dried on a silica gel column and feeds the reactor through the last opening. This nitrogen flow is supposed to remove all traces of air and water in the reactor. The anchor is actuated by means of a motor allowing a stirring speed of 40 to 120 rev / min. The reactor is immersed in a bath of silicone oil, thermostated at the chosen temperature.

Process: the PVA is introduced first into the reactor preheated to 200 ° C. The monomer preheated to 170 ° C. is introduced into the reactor immediately after the PVA with stirring. For initial PV A / CL mass ratios around 1, a homogeneous viscous mixture is obtained around 150-155 ° C. after a time of 10-20 min. The diffusion of the monomer beyond 150 ° C. into the PVA matrix is rapid, making it possible to have an amorphous and crystalline phase dissolution of the starting polymer. This aspect makes it possible to carry out syntheses in the molten state and below the melting point of the starting polymer. For the process described in this example, the set temperature is decreased from 200 to 175 ° C as the system melt. The initiator is then introduced at 175 ° C., diluted beforehand in an equivalent amount of monomer. The PVA, for this example, is a PVA KP 405 from the manufacturer Kuraray (Melting temperature = 191 ° C., Tg = 59 ° C.), with a molar mass of 25,000 g / mol (Kuraray data). The degree of hydrolysis is 82%. All other reagents (Aldrich) were used as such without any prior purification.

For this example, the mass quantities of reagents are: PVA = 400 g, epsilon-caprolactone = 500 g and tin bis (2-ethylhexnoate) as initiator = 4 g. Variable amounts of 8 to 32 g were also tested for other syntheses, giving equivalent results in terms of grafting. After five minutes of reaction, the conversion of the monomer is always greater than 95% and is 100% after ten minutes of reaction after the introduction of the monomer at 175 ° C. The average degree of polymerization measured is between 2.5 and 3.0. The monomer conversion rate and the average degree of polymerization were measured by 250 MHz and 400 MHz NMR spectroscopy in DMSO-d6 as a solvent. The conversion rate is measured as the ratio of the resonance area at 2.6 ppm (alpha-methylene to carbonyl in the monomer) to that at 2.25 ppm (methylene alpha-position of the carbonyl of the polymerized monomer) . The average degree of polymerization is measured by the ratio between the resonance areas at 2.25 ppm and 3.4 ppm (hydroxy-terminated polycaprolactone end-chain methylenes). Without initiator, the reaction time to have a total conversion of the monomer is 4 hours maximum. All samples are totally soluble in ethanol, unlike the starting PVA and polycaprolactone homopolymer.

2 - Example 2

The same method, the same method and the same analyzes as in Example 1 were used.

A polyethylene-co-vinyl alcohol copolymer EVOH (EVAL E105B) from the manufacturer EVAL Europe was used as the hydroxylated polymer in this example. It has an ethylene content of 44%. The formulation used for this example is: EVOH = 263g, epsilon-caprolactone = 500g and bis (2- ethylhexanoate) tin = 16g. Analysis on a sample after 15 minutes of reaction shows that the conversion of the monomer is complete. The average degree of polymerization measured is equal to 4 (FIG. 1).

3 - Example 3

A polyethylene-co-vinyl alcohol copolymer EVOH (EVAL E105B) from the manufacturer EVAL Europe was used as the hydroxylated polymer in this example. The formulation used for this example is: EVOH = 420 g, epsilon-caprolactone = 500 g and bis (2-ethylhexanoate) tin = 16 g. Analysis on a sample after 15 minutes of reaction shows that the conversion of the monomer is complete. The average degree of polymerization measured is equal to 2.2.

For the examples cited 1 to 3, the hydroxyl functions of the hydroxylated starting polymers are not all substituted by polylactone grafts. All samples are soluble in acetone and / or DMSO and / or ethanol. These tests prove the absence of homopolymer polylactone formation and the absence of unmodified hydroxylated polymer. All these materials are completely amorphous and have glass transition temperatures between -30 ^° C. and + 30 ^° C. The use of tin bis (2-ethylhexanoate) induces a coloration, for this process, which increases during time. This coloration remains weak for reaction times less than 15 min. All synthesized materials are more elastic and adhesive than the original EVOH or PVA. According to the recommended formulations and the nature of the initiator, the material may be totally amorphous or semi-crystalline. For the modified PVA, the reaction times limit secondary reactions such as alcoholysis reactions where acetate groups on the PVA chain come to esterify, by an exchange reaction, on the polycaprolactone chain ends, which are normally all complete. by hydroxy functions. Depending on the reaction time (2 to 6 hours), the temperature (above 150 ° C) and the As the amount of initiator, the number of acetate groups exchanging on EVOH chain ends may exceed 30% of the total number of acetate groups. Increasing the amount of initiator and the reaction time systematically induces for PVA and EVOH a continuous increase in viscosity, thus modifying its properties.

4 - Example 4

The same method, the same method and the same analyzes as in Example 1 were used. A polyethylene-co-vinyl alcohol copolymer EVOH (EVAL E105B) from the manufacturer EVAL Europe was used as the hydroxylated polymer in this example. The formulation used for this example is: EVOH = 6 g, epsilon-caprolactone = 207 g and bis (2-ethylhexanoate) tin = 0.5 g. Analysis on a sample after 15 minutes of reaction shows that the conversion of the monomer is complete. The average degree of polymerization measured is 18. In this example, the final material is semi-crystalline.

5 - Example 5

A polyethylene-co-vinyl alcohol copolymer EVOH (EVAL E105B) from the manufacturer EVAL Europe was used as the hydroxylated polymer in this example. The formulation used for this example is: EVOH = 6 g, epsilon-caprolactone = 415 g and bis (2-ethylhexanoate) tin = 0.5 g. Analysis on a sample after 15 minutes of reaction shows that the conversion of the monomer is complete. The average degree of polymerization measured is equal to 50. In this example, the final material is semi-crystalline.

Example 6 Reactive extrusion was successfully used for chemical modification of EVOH by Fepsilon-caprolactone. A CLEXTRAL BC 21 twin-screw extruder with interpenetrating modular screw profile was used. The diameter of the screws is 25 mm, the total length of the sheath 900 mm and the distance between the thread 21 mm. The materials obtained were extruded with a cylindrical die. The configuration of the screw profile used is shown in Table 1. The sheath was equipped with 9 independent heating zones of 10 cm each. The profile was chosen to allow the injection of the monomer mixed with the initiator into a zone where the hydroxylated polymer is already in the molten state.

The characteristics of each screw element are specified in Table 1 as well as the setpoint temperatures. The following symbols have been chosen to describe the profile: SE / 33/100: Screw element / pitch in mm / length in mm, RSE / 25/100: Inverse screw element / pitch in mm / length in mm, n KB / 90/25: number + mixing block / angle between two consecutive blocks / total length of the n associated blocks in mm.

Table 1: description of the screw profile and temperatures in the different zones. The reagents used are EVAL Europe EVOH E105B, epsilon caprolactone and tin bis (2-ethylhexanoate) (Aldrich). The EVOH was previously steamed 24h at 85 ^° C. under 1 mbar. The other reagents were used without prior purification. EVOH was introduced into zone 1 by means of a hopper with a flow rate of 1 kg / h. The speed of rotation of the screws was set at 60 rpm. The monomer was premixed at room temperature with the initiator and then injected by means of a pump into zone 3 after the reverse screw element (RSE / 25/25). The flow rate was measured at 1.3 kg / h. The flow rate at the outlet of the die was measured at 2.3 kg / h. Samples were taken directly out of the die. They are totally soluble in ethanol, unlike the polycaprolactone homopolymer and the starting EVOH. The proton NMR analyzes showed a total conversion of the monomer and made it possible to calculate average degrees of polymerization of 2.3 (FIG. 2). All the samples are completely colorless and EVOH thus modified is more elastic than the starting EVOH. The samples are totally soluble in ethanol.

7 - Example 7

This example illustrates the possibility of functionalizing a hydroxylated polymer modified with polycaprolactone in the molten state and at a temperature compatible for this type of reaction, avoiding any polymerization of a methacrylate function. The polycaprolactone grafted hydroxyl polymer used is that synthesized in Example 2. The objective is to introduce new functional groups on the modified polymer to give it new properties and applications. The method used is that described in Example 1. The formulation is as follows: EVOH modified in Example 2 = 400 g, methacrylic anhydride = 20 g, N-methylimidazole = 2 g, 2,6-di-tert-butyl-p methylphenol = 0.02 g (inhibitor).

The reaction was carried out at 120 ^° C. for one hour. The starting material modified with methacrylic anhydride is completely soluble in DMSO. A sample after reaction, previously purified of these reagents by means of a Sohxlet extractor (dichloromethane, 24 H) shows by infrared analysis the presence of an absorption band characteristic of the double bond of the grafted methacrylate group.

8 - Example 8

An EVOH-g-PCL film was produced using a SCAMIA RH 2 SCMIA single-screw extruder equipped with a 100 mm wide flat die and a speed-adjustable drawbench.

The extruder used was 25 mm in diameter and 650 mm in length. The sheath was thermostated at 150 ° C. and the die at 145 ° C. The material used was the material synthesized in Example 6, previously cold-milled. Mass flow was adjusted by screw speed (20 rpm) to 1.07 kg / h. The extrudate is recovered on a teflon chill roll and cooled and stretched by the drawing bench. The films thus obtained have thicknesses of between 20 and 200 μm.

References

[1] Stridsbert, Ryner, Albertsson, Advances in Polymer Science 157, 42-65 2002.

[2] Park, Kim, Yoon Journal of Polymer Science: Part B, Polymer Physics 40, 2561-2569 2002.

[3] Toselli, Fabbri, Monari, Pilati, Pizzoli, The Mantia, Scaffaro Macromol. Symp. 176, 233-244 2001.

[4] Aoi, Okada Macromol. Chem. Phys.203, 7, 1018-1028 2002.

Claims

1 / EVOH graft-polylactone synthesis process comprising the following steps: a homogeneous, solvent-free mixture comprising at least EVOH, at least one monomer comprising a lactone ring and at least one catalyst or initiator is produced; ; the polymerization reaction is stopped after a period of less than one hour.

2 / A method according to claim 1, characterized in that the EVOH comprises at least 1% of vinyl alcohol unit.

3 / A method according to claim 1 or 2, characterized in that the monomer comprises a lactone type ring of 4 to 10 units, substituted or not.

4 / A method according to one of claims 1 to 3, characterized in that the catalyst or initiator is organometallic, preferably alkoxy metal or metal carboxylate type, more preferably tin bis (2-ethylhexanoate).

5 / A method according to one of claims 1 to 4, characterized in that the homogeneous mixture is made by melting the EVOH before or simultaneously with the introduction of the monomer.

6 / A method according to one of claims 1 to 4, characterized in that the homogeneous mixture is produced by dissolving the EVOH in the lactone monomer. Process according to one of Claims 1 to 6, characterized in that the process is carried out at a temperature of between -60 ° C and + 60 ° C of the melting temperature of the EVOH.

8 / A method according to one of claims 1 to 7, characterized in that it takes place in a closed reactor with stirring or continuously in an extruder.

9 / A method according to one of claims 1 to 8, characterized in that the mixture consists of 100 parts by weight of EVOH containing n moles of hydroxy function, n / 100 to 100 n moles of monomer and n / 1000 to n / 5 moles of catalyst or initiator.

10 / EVOH-graft-polylactone obtainable by the method according to one of claims 1 to 9.

11 / EVOH-graft-polylactone according to claim 10, characterized in that it is EVOH-g-PCL.

12 / Process for the preparation of an EVOH-graft-polylactone derivative, characterized in that the hydroxyl or ester functions of the grafted EVOH-polylactone are reacted according to claim 10 or 11.

13 / EVOH graft-polylactone derivative obtainable by the process according to claim 12.

14 / Use of EVOH-graft-polylactone according to claim 10 or 11, or a derivative according to claim 13, for the formation of a film.

15 / Use of EVOH-graft-polylactone according to claim 10 or 11, or a derivative according to claim 13, as a flexibility agent. 16 / Use of EVOH graft-polylactone according to claim 10 or 11, or a derivative according to claim 13, as compatibilizer.

17 / Use of EVOH-graft-polylactone according to claim 10 or 11, or a derivative according to claim 13, as an adhesive.