PROCESS FOR CONTROLLING THE STRUCTURE OF A BLOCK COPOLYMER BY SELECTIVE COPOLYMERIZATION, BY RING OPENING, OF CYCLIC CARBONATE AND LACTONE MONOMERS

Abstract

The invention relates to a process for controlling the structure of a block copolymer by selective copolymerization, by ring opening, of cyclic carbonate and lactone monomers in the presence of a catalyst based on methanesulfonic acid, the said process comprising a sequence of stages carried out strictly in the following order: a) dissolving the cyclic carbonate monomer in a nonchlorinated aromatic solvent, b) adding, to the monomer solution, a bifunctional initiator chosen from diols or water, c) adding methanesulfonic acid (MSA) as catalyst of the polymerization reaction, d) when all the cyclic carbonate has been consumed, a telechelic polycarbonate capable of acting as macroinitiator of polymerization of the lactone is obtained, e) adding the lactone to the reaction medium in order to selectively obtain a block copolymer.

Claims

1-7. (canceled)

8. A process for controlling the structure of a block copolymer by selective copolymerization, by ring opening, of cyclic carbonate and lactone monomers in the presence of a catalyst based on methanesulfonic acid, comprising in succession: (a) dissolving a cyclic carbonate monomer in a nonchlorinated aromatic solvent to produce a monomer solution, followed by (b) adding a bifunctional initiator chosen from diols or water to the monomer solution from (a), followed by (c) adding methanesulfonic acid (MSA) to the solution from (b), followed by (d) polymerizing the cyclic carbonate monomer in the solution from (c), wherein when all the cyclic carbonate has been consumed, a telechelic polycarbonate capable of acting as macroinitiator of polymerization of the lactone is obtained, and followed by (e) adding the lactone to the reaction medium from (d) in order to selectively obtain a block copolymer.

9. The process of claim 8, wherein the cyclic carbonate is trimethylene carbonate (TMC), the lactone is s-caprolactone (s-CL), and the block copolymer is a P(CL-b-TMC-b-CL) triblock copolymer.

10. The process of claim 9, wherein the molar ratio of monomers to bifunctional initiator, TMC/s-CL/bifunctional initiator, is between 60/60/1 and 120/240/1.

11. The process of claim 8, wherein the bifunctional initiator/methanesulfonic acid (MSA) molar ratio is between 1/1 and 1/3.

12. The process of claim 8, which is conducted at a temperature of between 20 and 120 C.

13. The process of claim 8, which is conducted at a temperature of between 30 C. and 60 C.

14. The process of claim 8, wherein the nonchlorinated aromatic solvent is toluene, ethylbenzene or xylene.

15. The process of claim 8, wherein the cyclic carbonate is trimethylene carbonate (TMC).

16. The process of claim 8, wherein the lactone is s-caprolactone (s-CL).

17. The process of claim 8, wherein the nonchlorinated aromatic solvent is toluene.

18. The process of claim 8, wherein the block copolymer obtained is a P(CL-b-TMC-b-CL) triblock copolymer.

19. The process of claim 8, wherein the bifunctional initiator comprises water.

20. The process of claim 8, wherein the bifunctional initiator comprises a diol.

21. The process of claim 8, which is conducted continuously or batchwise.

22. The process of claim 8, wherein the block copolymer exhibits a linear morphology.

23. The process of claim 8, wherein the block copolymer is obtained free from contamination by other copolymers or homopolymers.

24. The process of claim 8, wherein the block copolymer is a triblock copolymer.

25. The process of claim 8, wherein the block copolymer contains nanodomains.

26. A PCL-b-PTMC-b-PCL block copolymer obtained by the process of claim 8, wherein each of the PCL blocks exhibits a degree of polymerization of between 30 and 120 and a number-average molecular weight Mn of between 3400 and 13680 g/mol, and the PTMC block exhibits a degree of polymerization of between 60 and 120 and a number-average molecular weight Mn of between 6100 and 12200 g/mol.

Description

DESCRIPTION OF THE INVENTION

[0030] As preamble, it is specified that the expression of between used in the context of this description should be understood as including the limits cited.

[0031] The term monomer as used refers to a molecule which can undergo a polymerization.

[0032] The term polymerization as used refers to the process for the conversion of a monomer or of a mixture of monomers into a polymer, the structure of which essentially comprises the multiple repetition of units derived from monomer molecules of lower molecular weight.

[0033] Polymer is understood to mean either a copolymer or a homopolymer.

[0034] Copolymer is understood in particular to mean a polymer derived from at least two types of monomers or macromonomers, one at least of which is chosen from a lactone and the other from a cyclic carbonate.

[0035] Homopolymer is understood to mean a polymer derived from just one type only of monomer or macromonomer.

[0036] Block copolymer is understood to mean a polymer comprising one or more uninterrupted sequences of each of the separate polymer types, the polymer sequences being chemically different from each other or from one another and being bonded together by a covalent bond.

[0037] The process for controlling the structure of a block copolymer according to the invention is carried out by selective copolymerization, by reopening, of cyclic carbonate and lactone monomers in the presence of a catalyst based on methanesulfonic acid.

[0038] Preferably, the cyclic carbonate monomer is trimethylene carbonate (TMC) and the lactone is -caprolactone (-CL). The block copolymer synthesized according to this control process is advantageously a PCL-b-PTMC-b-PCL triblock copolymer, the central block of which is PTMC, formed during a first phase of the selective copolymerization.

[0039] This selective copolymerization advantageously comprises a sequence of stages carried out strictly in a predetermined order. A first step consists in dissolving the cyclic carbonate monomer, in particular the TMC, in a nonchlorinated aromatic solvent.

[0040] The nonchlorinated aromatic solvent can be chosen from toluene, ethylbenzene or xylene. However, toluene is preferred to the other two solvents.

[0041] A second stage subsequently consists in adding, to the solution of TMC monomer, a bifunctional initiator comprising at least two hydroxyl functional groups. This initiator can in particular be chosen from diols or water. Methanesulfonic acid (MSA), which acts as catalyst of the reaction for the polymerization of TMC, is then added to the reaction medium.

[0042] By virtue of the use of water or of a diol as initiator of the polymerization of the TMC, in the presence of MSA in order to catalyse the reaction, a telechelic PTMC polymer, that is to say a PTMC polymer carrying a hydroxyl function group at each of its ends, is formed. This is because, as illustrated in Scheme 2 below, the opening of the TMC by nucleophilic addition of a water molecule forms a carbonic acid which spontaneously releases carbon dioxide CO.sub.2 to produce propane-1,3 diol. The propane-1,3 diol thus formed then acts as bifunctional initiator of the polymerization of the TMC according to the activated monomer AM propagation mechanism. The PTMC polymer thus formed is a telechelic polymer, the structure of which is entirely identical to that of the PTMC polymer formed according to the competing mechanism, by active chain end ACE. Consequently, just one population of dihydroxylated PTMC polymer is obtained at this stage.

##STR00002##

[0043] When all the cyclic carbonate monomer is consumed, that is to say when all the TMC is consumed, just one telechelic polycarbonate, in particular the dihydroxylated PTMC polymer, present in the reaction medium is obtained. This polymer can then act, in a second phase of the selective copolymerization process, as macroinitiator of polymerization of the lactone, in particular of -caprolactone, -CL.

[0044] In order to carry out this second polymerization, the lactone is thus added to the reaction medium. Just one population of PCL-b-PTMC-b-PCL triblock copolymers is then selectively obtained, according to the reaction Scheme 3 below.

##STR00003##

[0045] This strict sequence of the stages of synthesis of the block copolymer makes it possible to obtain a defined structure, free of contamination by homopolymers or by other types of block or random copolymers. When the order of addition is reversed (first the -CL and subsequently the TMC), the block copolymer obtained is contaminated by PTMC homopolymer. Control of the structure is very important as contamination by other types can disrupt the structuring by phase segregation.

[0046] A very important characteristic of the block copolymers is the phase segregation of the blocks, which separate to give nanodomains. This phase separation depends essentially on two parameters. A first parameter, designated Flory-Huggins interaction parameter and denoted , makes it possible to control a size of the nanodomains. More particularly, it defines the tendency of the blocks of the block copolymer to separate into nanodomains. The product N, of the degree of polymerization N and of the Flory-Huggins parameter , gives an indication with regard to the compatibility of two blocks and if they can separate. For example, a diblock copolymer with a strictly symmetrical composition separates into microdomains if the product N is greater than 10.49. If this product N is less than 10.49, the blocks become mixed and the phase separation is not observed at the observation temperature.

[0047] Consequently, in order to be able to observe phase segregation between the blocks of the triblock copolymer synthesized according to the process of the invention, the degree of polymerization of the blocks has to be sufficiently high. The concentration of each monomer in the reaction medium can thus vary to a certain extent.

[0048] This is the reason why the monomers/initiator (TMC/-CL/initiator) molar ratio is preferably between 60/60/1 and 120/240/1. This is because a lower ratio, for example 40/40/1, does not make it possible to observe phase segregation.

[0049] Thus, for a degree of polymerization of the PCL varying between 60 and 240 (30 and 120 per block respectively), PCL blocks for which the number-average molecular weight Mn is between 3400 and 13680 g/mol are obtained. Likewise, for a degree of polymerization of the PTMC of between 60 and 120, PTMC blocks for which the number-average molecular weight Mn is between 6100 and 12200 g/mol are obtained.

[0050] It is possible to vary the amount of MSA catalyst employed in the process, in order to adjust the reaction time without affecting the control of the polymerization. Normally, it is preferable for the molar ratio of the dihydroxylated initiator to the MSA catalyst to be of the order of 1. However, it can vary between 1/1 and 1/3.

[0051] The catalyst can be easily removed at the end of the reaction by neutralization using a hindered organic base, such as diisopropylethylamine (DIEA), or a tertiary amine supported on a resin of polystyrene type.

[0052] The bifunctional initiator is chosen from diols or water. In general, the triblock copolymer synthesized with such an initiator exhibits a linear morphology. However, when the initiator is provided in the form of a polyhydroxylated polymer, such as, for example, glycerol, pentaerythritol, dipentaerythritol, trimethylolethane, trimethylolpropane, or sorbitol, it can make it possible to obtain triblock copolymers exhibiting a star-branched morphology.

[0053] This process is preferably carried out at a temperature ranging from 20 to 120 C. and more preferably between 30 and 60 C., in particular when the solvent is toluene. This is because it is possible to obtain, at a temperature of the order of 30 C., PCL-b-PTMC-b-PCL block copolymers having molecular weights Mn of greater than 18000 g/mol in a few hours and with a yield of greater than or equal to 80% after purification.

[0054] In addition, this process is preferably carried out with stirring. It can be carried out continuously or batchwise.

[0055] Finally, the reactants used in this process are preferably dried before they are used, in particular by treatment under vacuum, distillation or drying by an inert dehydrating agent.

EXAMPLES

[0056] The following general procedure which is used to carry out the processes described below.

[0057] The alcohols were distilled over sodium. The toluene is dried using an MBraun SPS-800 solvent purification system. The trimethylene carbonate TMC was dried in a dry tetrahydrofuran (THF) solution over calcium dihydride (CaH.sub.2) and recrystallized three times from cold THF. The methanesulfonic acid (MSA) was used without additional purification. The diisopropylethylamine (DIEA) was dried and distilled over CaH.sub.2 and stored over potassium hydroxide (KOH).

[0058] The Schlenk tubes were dried with a heat gun under vacuum in order to remove any trace of moisture.

[0059] The reaction was monitored by .sup.1H NMR (proton nuclear magnetic resonance) on a Brucker Avance 300 and 500 device and by size exclusion chromatography (SEC) in THF. To do this, samples were withdrawn, neutralized with DIEA, evaporated and taken up in an appropriate solvent for the purpose of their characterization. .sup.1H NMR makes it possible to quantify the degrees of polymerization (DPs) of the TMC and -CL monomers by determining the integration ratio of half of the signals of the CH.sub.2 groups carrying the OC(O)O functional group and the CO functional group respectively to the signals of the CH.sub.2 protons carrying the OH functional group initially on the initiator. The spectra are recorded in deuterated chloroform on a 500 or 300 MHz spectrometer according to the examples. The number-average molecular weight Mn, the weight-average molecular weight Mw and the polydispersity index (PDI) of the samples of copolymers withdrawn are measured by size exclusion chromatography SEC in THF with polystyrene calibration.

[0060] The measurement by differential scanning calorimetry, denoted DSC, makes it possible to study the glass transitions and the crystallization. DSC is a thermal analysis technique which makes it possible to measure the differences in the exchanges of heat between a sample to be analyzed and a reference during phase transitions. A Netzsch DSC204 differential scanning calorimeter was used to carry out this study.

[0061] The calorimetry analyses were carried out between 80 and 130 C. and the T.sub.g and T.sub.m values were recorded during the second rise in temperature (at a rate of 10 C./min).

Example 1 (Comparative): Preparation of a PCL-b-PTMC Diblock Copolymer (with Introduction of -CL First into the Reaction Medium)

[0062] The initiator, n-pentanol, (9 l, 0.08 mmol, 1 equiv.) and methanesulfonic acid (0.2 mmol, 3 equiv.) are successively added to a solution of -caprolactone (700 L, 6.6 mmol, 80 equiv.) in toluene (7.3 ml, [-CL].sub.0=0.9 mol/l). The reaction medium is stirred at 30 C. under argon for 2 h. Once the -CL monomer has been completely consumed, which is established by monitoring by .sup.1H NMR, the trimethylene carbonate TMC (675 mg, 6.6 mmol, 80 equiv.) is added to the reaction medium and the solution is stirred at 30 C. under argon for 7 h. An excess of diisopropylethylamine (DIEA) is subsequently added in order to neutralize the catalyst, and the solvent is evaporated under vacuum. The polymer obtained is then dissolved in the minimum amount of dichloromethane, precipitated by addition to cold methanol, filtered off and dried under vacuum.

The results obtained are as follows:

[0063] A PCL.sub.80-b-PTMC.sub.80 copolymer is obtained with a degree of conversion of greater than 96% and a yield of 90%.

[0064] .sup.1H NMR (CDCl.sub.3, 500 MHz): 4.24 (t, 4H80, J=6.0 Hz, OCH.sub.2CH.sub.2CH.sub.2O), 4.13 (t, 2H, J=6.5 Hz, OCH.sub.2, CL-TMC diad), 4.06 (t, 2H80, J=7.0 Hz, OCH.sub.2(CH.sub.2).sub.4C(O)), 3.74 (t, >2H, J=6.0 Hz CH.sub.2OH, TMC end), 2.30 (t, 2H80, J=7.5 Hz, C(O)CH.sub.2(CH.sub.2).sub.4O), 2.05 (m, 2H80, OCH.sub.2CH.sub.2CH.sub.2O), 1.64 (m, 4H80, OCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O)), 1.38 (m, 2H80, O(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O)), 0.90 (t, 3H, J=7.0 Hz, CH.sub.3); [0065] SEC (THF): Mn15 650 g/mol, PDI: Mw/Mn1.1.

[0066] The integration of the signal corresponding to the CH.sub.2OH ending of the PTMC block is markedly greater than 2, indicating the presence of polymer chains other than those initiated by the hydroxylated polycaprolactone PCL-OH. This thus means that the PCL-b-PTMC diblock copolymer synthesized is not alone but mixed with another PTMC homopolymer of telechelic type.

Example 2 (Comparative): Preparation of a PTMC-b-PCL-b-PTMC Triblock Copolymer (with Introduction of -CL First)

[0067] The initiator, butane-1,4-diol (0.8 ml, 8.9 mmol, 1 equiv.) and methanesulfonic acid (0.27 mL, 4.5 mmol, 0.5 equiv.) are successively added to a solution of -caprolactone (23.2 mL, 0.219 mol, 25 equiv.) in toluene (230 mL, [-CL].sub.0=0.9 mol/L). The reaction medium is stirred at 30 C. under argon for 6 h 30. Once the -CL monomer has been completely consumed, we establish by monitoring by .sup.1H NMR, the trimethylene carbonate TMC (25 g, 0.245 mol, 27 equiv.) is added to the reaction medium and the solution is stirred under argon at 30 C. for 2.5 h. An excess of diisopropylethylamine (DIEA) is subsequently added to neutralize the catalyst, and the solvent is evaporated under vacuum. The polymer obtained is then dissolved in the minimum amount of dichloromethane, precipitated by addition to cold methanol, filtered off and dried under vacuum.

The results obtained are as follows:

[0068] A PTMC-b-PCL-b-PTMC copolymer is obtained with a degree of conversion of greater than 96% and a yield of 85%.

[0069] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.23 (t, 4H24.5, J=6.3 Hz, n OCH.sub.2CH.sub.2CH.sub.2O), 4.12 (t, 4H, J=6.7 Hz, (CH.sub.2).sub.5C(O)OCH.sub.2CH.sub.2CH.sub.2), 4.05 (t, 2H22.5, J=6.6 Hz, OCH.sub.2(CH.sub.2).sub.4C(O)), 3.73 (m, >4H, HOCH.sub.2(CH.sub.2).sub.2), 2.30 (t, 2H21.5, J=7.5 Hz, COCH.sub.2(CH.sub.2).sub.4O), 2.04 (m, 2H24.8+4H, n OCH.sub.2CH.sub.2CH.sub.2O and OCH.sub.2CH.sub.2CH.sub.2OH), 1.90 (m, 4H, OCH.sub.2(CH.sub.2).sub.2CH.sub.2O), 1.64 (m, 4H22+4H, OCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O) and HOCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O)), 1.38 (m, 2H22+2H+2H, O(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O) and HO(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O)).

[0070] The integration of the signal corresponding to the CH.sub.2OH ending of the PTMC block is greater than 4, indicating the presence of polymer chains other than those initiated by the dihydroxylated polycaprolactone HO-PCL-OH. This thus means that the PTMC-b-PCL-b-PTMC triblock copolymer synthesized is not alone but mixed with another PTMC homopolymer of telechelic type. [0071] SEC (THF): Mn4900 g/mol, PDI: Mw/Mn1.19; [0072] SEC (THF): Mn4900 g/mol, Mw/Mn1.19; [0073] DSC: T.sub.g1=48.6 C., T.sub.m=42.1 C.

Example 3 (Invention): Preparation of a PCL-b-PTMC-b-PCL Triblock Copolymer with an -CL/TMC Ratio of 2/1

[0074] The initiator, water, (2 l, 0.10 mmol, 1 equiv.) and methanesulfonic acid (22 l, 0.30 mmol, 3 equiv.) are successively added to a solution of TMC (907 mg, 8.9 mmol, 80 equiv.) in toluene (9.0 ml, [TMC]o=0.98 mol/l). The reaction medium is stirred at 30 C. under argon for 6 h 30. Once the TMC monomer has been completely consumed, which is established by monitoring by .sup.1H NMR, the -CL (1.9 mL, 160 equiv.) is added and the solution is stirred at 30 C. under argon for 8 h. An excess of diisopropylethylamine (DIEA) is subsequently added in order to neutralize the catalyst, and the solvent is evaporated under vacuum. The polymer is then dissolved in the minimum amount of dichloromethane, precipitated by addition to cold methanol, filtered off and dried under vacuum.

The results obtained are as follows:

[0075] A PCL-b-PTMC-b-PCL copolymer is obtained with a degree of conversion of greater than 96% and a yield of 85%.

[0076] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.23 (t, 4H52, J=6.3 Hz, n OCH.sub.2CH.sub.2CH.sub.2O), 4.12 (t, 4H, J=6.7 Hz, (CH.sub.2).sub.5C(O)OCH.sub.2CH.sub.2CH.sub.2), 4.05 (t, 2H101, J=6.6 Hz, OCH.sub.2(CH.sub.2).sub.4C(O)), 3.64 (t, 4H, J=6.5 Hz, HOCH.sub.2(CH.sub.2).sub.4), 2.30 (t, 2H107, J=7.5 Hz, COCH.sub.2(CH.sub.2).sub.4O), 2.04 (m, 2H53+4H, n OCH.sub.2CH.sub.2CH.sub.2O and OCH.sub.2CH.sub.2CH.sub.2OH), 1.64 (m, 4H110+4H, OCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O) and HOCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O)), 1.38 (m, 2H108+2H+2H, O(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O) and HO(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O)).

[0077] The absence of triplet signal at 3.74 ppm (corresponding to the CH.sub.2OH group of an end TMC unit) indicates that all the polymer chains have CH.sub.2OH ends of a caprolactone unit (t signal at 3.64 ppm). This confirms the absence of telechelic PTMC homopolymer. [0078] SEC (THF): Mn29 370 g/mol, PDI: Mw/Mn1.18; [0079] DSC: T.sub.g1=55 C., T.sub.g2=27 C., T.sub.m=53 C.

[0080] The two glass transition temperatures Tg1 and Tg2 identified are similar to the glass transition temperatures of each PCL and PTMC homopolymer respectively, indicating the observation of a phase segregation between the blocks.

Example 4 (Invention): Preparation of a PCL-b-PTMC-b-PCL Triblock Copolymer with an -CL/TMC Ratio of 1/1

[0081] The initiator, butane-1,4-diol (4 l, 0.046 mmol, 1 equiv.) and methanesulfonic acid (18 l, 0.3 mmol, 6 equiv. (3 per hydroxyl function group)) are successively added to a solution of TMC (381 mg, 3.73 mmol, 80 equiv.) in toluene (7.2 ml, [TMC]o=0.5 mol/l). The reaction medium is stirred at 40 C. under argon for 2 h 30. Once the TMC monomer has been completely consumed, which is established by monitoring .sup.1H NMR, the -CL (420 l, 3.96 mmol, 80 equiv.) is added and the solution is stirred at 40 C. under argon for 1 h. An excessive diisopropylethylamine (DIEA) is subsequently added in order to neutralize the catalyst, and the solvent is evaporated under vacuum. The polymer is then dissolved in the minimum amount of dichloromethane, precipitated by addition to cold methanol, filtered off and dried under vacuum.

The results obtained are as follows:

[0082] A PCL-b-PTMC-b-PCL copolymer is obtained with a degree of conversion of greater than 96% and a yield of 83%.

[0083] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.23 (t, 4H50, J=6.3 Hz, n OCH.sub.2CH.sub.2CH.sub.2O), 4.12 (t, 4H, J=6.7 Hz, (CH.sub.2).sub.5C(O)OCH.sub.2CH.sub.2CH.sub.2), 4.05 (t, 2H46, J=6.6 Hz, OCH.sub.2(CH.sub.2).sub.4C(O)), 3.64 (t, 4H, J=6.5 Hz, HOCH.sub.2(CH.sub.2).sub.4), 2.30 (t, 2H46, J=7.5 Hz, COCH.sub.2(CH.sub.2).sub.4O), 2.04 (m, 2H50+4H, n OCH.sub.2CH.sub.2CH.sub.2O and OCH.sub.2CH.sub.2CH.sub.2OH), 1.64 (m, 4H46+4H, OCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O) and HOCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O)), 1.38 (m, 2H46+2H+2H, O(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O) and HO(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O)).

[0084] The absence of triplet signal at 3.74 ppm (corresponding to the CH.sub.2OH group of an end TMC unit) indicates that all the polymer chains have CH.sub.2OH ends of a caprolactone unit (t signal at 3.64 ppm). This confirms the absence of telechelic PTMC homopolymer. [0085] SEC (THF): Mn17 800 g/mol, PDI: Mw/Mn1.17; [0086] DSC: T.sub.g1: not observed; T.sub.g2=28.9 C., T.sub.m=47.7 C.

[0087] The T.sub.g value observed (28.9 C.) is similar to the glass transition temperature of the PTMC homopolymer, indicating the observation of a phase segregation between the PTMC and PCL blocks. The size and the semicrystalline nature of the PCL block makes it difficult to observe the T.sub.g1 corresponding to this block.

Example 5 (Invention): Preparation of a PCL-b-PTMC-b-PCL Triblock Copolymer with an -CL/TMC Ratio of 1/2

[0088] The initiator, butane-1,4-diol (4.6 l, 0.055 mmol, 1 equiv.) and methanesulfonic acid (21 l, 0.30 mmol, 3 equiv.) are successively added to a solution of TMC (450 mg, 4.4 mmol, 80 equiv.) in toluene (8.4 ml, [TMC]o=0.5 mol/l). The reaction medium is stirred at 40 C. under argon for 2 h 30. Once the TMC monomer has been completely consumed, which is established by monitoring by .sup.1H NMR, the -CL (245 l, 40 equiv.) is added and the solution is stirred at 40 C. under argon for 30 min. An excess of diisopropylethylamine (DIEA) is subsequently added in order to neutralize the catalyst, and the solvent is evaporated under vacuum. The polymer is then dissolved in the minimum amount of dichloromethane, precipitated by addition to cold methanol, filtered off and dried under vacuum.

The results obtained are as follows:

[0089] A PCL-b-PTMC-b-PCL copolymer is obtained with a degree of conversion of greater than 96% and a yield of 81%.

[0090] .sup.1H NMR (CDCl.sub.3, 300 MHz): 4.23 (t, 4H55, J=6.3 Hz, n OCH.sub.2CH.sub.2CH.sub.2O), 4.12 (t, 4H, J=6.7 Hz, (CH.sub.2).sub.5C(O)OCH.sub.2CH.sub.2CH.sub.2), 4.05 (t, 2H26, J=6.6 Hz, OCH.sub.2(CH.sub.2).sub.4C(O)), 3.64 (t, 4H, J=6.5 Hz, HOCH.sub.2(CH.sub.2).sub.4), 2.30 (t, 2H26, J=7.5 Hz, COCH.sub.2(CH.sub.2).sub.4O), 2.04 (m, 2H55+4H, n OCH.sub.2CH.sub.2CH.sub.2O and OCH.sub.2CH.sub.2CH.sub.2OH), 1.64 (m, 4H26+4H, OCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O) and HOCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2C(O)), 1.38 (m, 2H26+2H+2H, O(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O) and HO(CH.sub.2).sub.2CH.sub.2(CH.sub.2).sub.2C(O)).

[0091] The absence of triplet signal 3.74 ppm (corresponding to the CH.sub.2OH group of an end TMC unit) indicates that all the polymer chains have CH.sub.2OH ends of the caprolactone unit (t signal at 3.64 ppm). This confirms the absence of telechelic PTMC homopolymer. [0092] SEC (THF): Mn13 300 g/mol, PDI: Mw/Mn1.18; [0093] DSC: T.sub.g1: not observed; T.sub.g2=22.5 C., T.sub.m=39.5 C.

[0094] The T.sub.g value observed (22.5 C.) is similar to the glass transition temperature of the PTMC homopolymer, indicating the observation of a phase segregation between the PTMC and PCL blocks. The size and the semicrystalline nature of the PCL block makes it difficult to observe the T.sub.g1 corresponding to this block.