PROCESS FOR PREPARING POLYDIENE/POLYLACTIDE COPOLYMERS BY REACTIVE EXTRUSION

Abstract

The present invention relates to a process for preparing a diene elastomer/polylactide copolymer, the weight percentage of polylactide being between 10% and 45% by weight, relative to the weight of the copolymer, characterized in that lactide, an elastomer functionalized by at least one group bearing at least one function capable of initiating a ring-opening polymerization of the lactide and a catalytic system are introduced into an extruder (A).

Claims

1.-17. (canceled)

18. A process for preparing a diene elastomer/polylactide copolymer comprising the step of introducing into an extruder: lactide; an elastomer functionalized by at least one group bearing at least one function capable of initiating a ring-opening polymerization of the lactide, the functionalized elastomer having a number-average molar mass, Mn, of greater than 40,000 g/mol; and a catalytic system, wherein a weight percentage of polylactide is between 10% and 45% by weight, relative to a weight of the diene elastomer/polylactide copolymer.

19. The process according to claim 18, wherein the step of introducing into an extruder comprises the steps of: introducing the lactide and the functionalized elastomer into an extruder; mixing the lactide and the functionalized elastomer to obtain a mixture; then introducing the catalytic system into the mixture, the introduction of the catalytic system triggering polymerization; then introducing a catalyst inhibitor to stop polymerization; recovering the diene elastomer/polylactide copolymer at an outlet of the extruder.

20. The process according to claim 18, wherein polymerization is carried out at a temperature ranging from 80° C. to 200° C.

21. The process according to claim 18, wherein polymerization time is less than 30 minutes.

22. The process according to claim 18, wherein a weight percentage of lactide introduced ranges from 12% to 47% by weight, relative to the total weight of functionalized diene elastomer introduced and lactide introduced.

23. The process according to claim 18, wherein polymerization is carried out in bulk.

24. The process according to claim 18, wherein the process is a continuous process.

25. The process according to claim 24, wherein the function capable of initiating a ring-opening polymerization of the lactide is a primary amine —NH.sub.2 or a hydroxyl —OH.

26. The process according to claim 18, wherein an antioxidant is also introduced.

27. The process according to claim 19, wherein an antioxidant is also introduced with the lactide and the functionalized elastomer.

28. The process according to claim 18, wherein the diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers, ethylene/diene copolymers, and blends thereof.

29. The process according to claim 18, wherein, in the diene elastomer/polylactide copolymer, the weight percentage of polylactide ranges from 15% to 40% by weight, relative to the weight of the diene elastomer/polylactide copolymer.

30. The process according to claim 18, wherein the diene elastomer is functionalized by two end groups.

31. The process according to claim 30, wherein the number-average molar mass, Mn, of the diene elastomer ranges from more than 40,000 g/mol to 250,000 g/mol.

32. The process according to claim 30, wherein the number-average molar mass, Mn, of the diene elastomer ranges from 50,000 g/mol to 200,000 g/mol.

33. The process according to claim 18, wherein the diene elastomer is functionalized by several pendant groups along the backbone.

34. The process according to claim 33, wherein the number-average molar mass, Mn, of the diene elastomer ranges from 100,000 g/mol to 500,000 g/mol.

35. The process according to claim 18, wherein the diene elastomer/polylactide copolymer is a triblock, of structure PLA-diene elastomer-PLA, having a number-average molar mass, Mn, ranging from 50,000 g/mol to 300,000 g/mol.

36. The process according to claims 18, wherein the diene elastomer/polylactide copolymer is a comb copolymer, having a diene elastomer backbone and pendant PLA blocks along the backbone, having a number-average molar mass, Mn, ranging from 100,000 g/mol to 600,000 g/mol.

Description

EXAMPLE 1

PLA-SBR-PLA Triblock Copolymers Obtained by Polymerization of Lactide on an Amine-Difunctionalized SBR by Reactive Extrusion

[0195] Aromatic primary amine-difunctionalized SBRs (styrene-butadiene rubbers) were tested. As control, use is made of a non-functionalized SBR with a higher Mn so as to be closer to the Mn of the copolymers synthesized.

[0196] The aromatic primary amine-difunctionalized SBRs were synthesized according to the following protocol, described in detail herein for a difunctionalized SBR of 87 300 g/mol:

[0197] Preparation of the Solution of Initiator (Si):

[0198] The following are successively added into a reactor of 30 l in total: 11.5 l of methylcyclohexane (MCH), 1 l of 4-bromo-N,N-bis(trimethylsilyl)aniline (sparged beforehand with nitrogen), 5.35 l of a solution of s-BuLi at 1.4 mol/l in cyclohexane and 0.35 mol of tetramethylethylenediamine (TMED) purified beforehand on Al.sub.2O.sub.3.

[0199] The reaction is left at ambient temperature for 24 h. This solution is then stored at 15° C.-20° C. under nitrogen before use. This solution is subsequently referred to as “Si solution”.

[0200] Polymerization and Coupling:

[0201] The following various constituents are successively added into the reactor: 56 l of MCH, 350 ppm of tetrahydrofuran (THF), 2.7 kg of styrene, 5 kg of butadiene, 65 ml of n-BuLi (0.1 mol/l) and 1.07 1 of the Si solution.

[0202] After 50 min at 50° C., conversion is 70%, and 0.48 equivalent of Me.sub.2SiCl.sub.2 relative to the Li.sup.+ is added for the coupling. The reaction mixture is stirred at 60° C. for 30 min. 0.4% by weight, relative to the weight of the elastomer, of an Irganox® 2246 (2,2′-methylenebis(6-t-butyl-4-methylphenol))/6PPD (80/20 m/m) mixture is then added.

[0203] Deprotection:

[0204] The deprotection conditions are the following: 2 eq of HCl/amine for 48 h at 80° C. Once the deprotection reaction has ended, the reaction medium is washed with raw water in order to extract the maximum amount of acid and to raise the pH of the aqueous phase to 7. A sodium hydroxide solution can be used to raise the pH above 7 (0.5 eq sodium hydroxide/HCl).

[0205] The polymer solution is then stripped, and the functionalized elastomer is dried in a rotary oven under nitrogen and then in an incubator at 60° C. under vacuum.

[0206] Results:

[0207] The number-average molar mass obtained is 87 300 g/mol (PI=1.1) and the content of functions is 0.2 mol % relative to the elastomer.

[0208] The microstructures and the macrostructures of these functionalized SBRs are given in the following table:

TABLE-US-00001 TABLE 1 Macrostructure Microstructure Mn (g/mol) PI % 1,4-PB % 1,2-PB % PS SBR-A 68 200 1.1 49.30% 36.10% 14.60% SBR-B 87 300 1.1 63.10% 24.10% 12.80% SBR-C 96 500 1.12 62.30% 24.20% 13.10% SBR- control 179 100  1.04 61.7% 20.7% 17.7%

[0209] A DSM Xplore microextruder with a capacity of 15 g is used.

[0210] Two processes were carried out:

[0211] P1: Addition without Sequencing

[0212] The functionalized SBR previously obtained (8.4 g), which has been predried, is incorporated into the microextruder at the same time as a (lactide/Sn(oct).sub.2/additives) mixture contained in a two-necked round-bottomed flask and prepared beforehand in a glovebox. The term “additives” denotes triphenylphosphine (P(Ph).sub.3) and/or U626 (antioxidant, Ultranox®626, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite). The temperature of the mixture is maintained at 170° C. [0213] 1. Introduction of the SBR/lactide/catalyst/additives into the microextruder (Tmixture=170° C., Sscrews=60 rpm) [0214] 2. Polymerization of the PLA (Tsetpoint=180° C., Tmixture=170° C., Sscrews=150 rpm) [0215] 3. When the torque has reached a plateau, introduction of the Cata-killer (Irganox® 1425, 28 mg) in order to stop the polymerization

[0216] P2: Sequenced Addition

[0217] Sequential introduction of the reagents: [0218] 1. Introduction of the functionalized SBR previously obtained (8.4 g) into the microextruder (Tsetpoint=180° C., Tmixture=170° C., Sscrews=60 rpm), of 77% of lactide and of U626. The lactide and the U626 were mixed beforehand in a glovebox in a two-necked round-bottomed flask. The SBR was dried beforehand. [0219] 2. Mixing/homogenization of the SBR and of the lactide at 150 rpm for 2 min [0220] 3. Introduction of the remaining 23% of lactide in the presence of the catalyst solution Sn(oct).sub.2/P(Ph).sub.3. The whole mixture being contained in a two-necked flask prepared beforehand in a glovebox. [0221] 4. Polymerization of the PLA (Tsetpoint=180° C., Tmixture=170° C., Sscrews=150 rpm) [0222] 5. When the couple reaches a plateau, introduction of the catalyst inhibitor (Irganox® 1425, 28 mg) to stop the polymerization

[0223] In the two cases, the functionalized SBR is dried beforehand for 12 h under vacuum at 60° C., until a residual water content of less than 300 ppm is obtained.

[0224] These processes, carried out in a microextruder, are batchwise. The various operating conditions are reported in the following table:

TABLE-US-00002 TABLE 2 SBR/LA [LA/Sn(oct).sub.2] [SBR/Sn(oct).sub.2] Sn/P U626 (% Matrix (g/g) mol mass mol total mass.) Process CP1 SBR-A 60/40 191 102 1/1 0.25% P2 CP2 SBR-A 60/40 200 107 1/1 0.07% P2 CP3 SBR-B 60/40 700 373 1/1 0.12% P2 CP4 SBR-B 80/20 700 373 1/1 0.06% P2 CP5 SBR-A 60/40 700 373 1/1 0.25% P2 CP6 SBR-B 60/40 700 373 1/1 0.12% P1 Control SBR 60/40 700 373 1/1 0.1% P2 CP control + 1-octanol

[0225] For each of the triblock copolymers obtained (CP1 to CP6), the appearance on the .sup.1H NMR spectra, of —Ph—NH—(C═O)— proton signals at about 7.88 ppm, characteristic of the PLA-SBR-PLA chains, is observed. These protons are logically absent on the spectrum of the material obtained from the nonfunctional SBR (control CP).

[0226] The SEC chromatograms of the materials obtained are consistent with the intended structures: [0227] For the polymerizations in the presence of the functional SBRs (intended triblock copolymers), the molar masses of the materials obtained are greater than that of the starting functional SBR. The increase in the molar masses is greater as the fraction of starting lactide increases. [0228] For the polymerization in the presence of the nonfunctional SBR and the 1-octanol (intended synthesis of a PLA homopolymer), the main unresolved peak of the SEC curve is at the same position as that of the starting elastomer. A small secondary unresolved peak, consistent with the obtaining of PLA homopolymer having a average molar mass close to 9500 g/mol, is observed.

[0229] The other results are reported in the following table:

TABLE-US-00003 TABLE 3 Conversion Mn tri- % by block PI tri- Fin comp .sup.1H Time Mn PLA (g/mol) block SBR/PLA NMR (min) (g/mol) .sup.1,2 SEC (SEC) (mass) .sup.1H NMR CP1 92% 9.5 15 000 117 700 2.1 65/35 CP2 91% 4.5 15 700 132 500 2.6 64/36 CP3 93% 8 15 600 133 600 1.9 65/35 CP4 86% 6 5500 112 100 2.3 84/16 CP5 94% 8 18 400 166 300 1.2 64/36 CP6 94% 6 15 600 132 600 3 65/35 Control 94% 45 9500 142 300 2.8 67/33 CP Mixture .sup.1 Mn of each PLA block calculated by the following formula: [00001]$M_n^{\mathrm{PLA}\mathrm{block}}=\frac{1}{2}.Math.\frac{M_n^{\mathrm{SBR},\mathrm{SE}C\mathrm{eq}.\mathrm{PS}}}{1-\%{\mathrm{massPLA}}^{\mathrm{NMR}}}.Math.\%{\mathrm{massPLA}}^{\mathrm{NMR}}$.sup.2 Mn of the PLA homopolymer determined by SEC in PS equivalent.

[0230] The vertical force exerted on the barrels by the extruded material beings to increase as soon as the catalytic system is introduced (arrow at about 10 min in FIG. 2A, at about 2 min in FIG. 2B). Then the force reaches a maximum which corresponds to the end of the polymerization (arrow at about 10 min in FIG. 2A, at about 8 min in FIG. 2B). The change in the vertical force for the CP5 and CP6 tests is given in FIG. 2 (FIGS. 2A and 2B respectively).

[0231] DSC

[0232] The results are reported in the following table, in which, when two melting peaks are observed, the two values are indicated:

TABLE-US-00004 TABLE 4 1.sup.st cycle 2.sup.nd cycle DSC Mp PLA (° C.) ΔHf PLA (J/g PLA) Tg SBR (° C.) CP3 153 9.1 −55 168 CP4 / 0 −55 CP2 151 5.6 −38 166 CP5 160 0.8 −55 170 CP6 / 0 −56 Control CP 164 41.5 −46

[0233] The presence of a crystalline phase of PLA is noted for the copolymers consisting of long PLA blocks (14 kg/mol (CP2) and 15 kg/mol (CP3)). The percentage crystallinity is however low given the enthalpies of fusion measured, of about 2 to 6 J/g (an annealing at 110° C. would make it possible to increase this value). This low crystallinity is explained by the presence of the central SBR block. 2 fusion peaks most certainly consistent with 2 different crystalline phase are observed on the thermograms. The melting points of the PLA phases are greater than 150° C. In the 2.sup.nd cycle, the Tg of the PLA close to 60° C. is clearly observed (Table 4).

[0234] The control mixture also shows a melting peak and the crystallinity is much higher (ΔHf=41 J/g).

[0235] Tensile Tests

[0236] The results are reported in the following table:

TABLE-US-00005 TABLE 5 TENSILE FORCE Tensile strength* (MPa) Elongation at break* (%) CP3 10.1 (0.44) 520 (25) CP4 1.9 (0.17) 540 (29) CP2 8.7 (0.37) 460 (10) Control mixture 0.3 16 (3) *the standard deviation has been indicated between parentheses

[0237] It is noted: [0238] That the elongation at break is high for the 3 copolymers (CP2, CP3, CP4) : from 460% to 540%. It is independent of the length of the PLA blocks. [0239] That the elongation at break increases with the length of the SBR block: CP2 with an SBR-A block of Mn=68 kg/mol has an elongation at break of 460%, while CP3 with an SBR-B block of Mn=87 kg/mol has an elongation at break of 520%. [0240] Conversely, the tensile strength appears to be dependent on the length of the PLA blocks: [0241] For the long blocks (14 kg/mol and 15 kg/mol, CP2 and CP3): tensile strength =8.7 to 10.1 MPa. [0242] For the short blocks (5 k, CP4): tensile strength=1.9 MPa [0243] Contrary to the copolymers, the control mixture has no mechanical strength.

[0244] DMA

[0245] The results are reported in the following table:

TABLE-US-00006 TABLE 6 DMA (Tg determined by inflection Tg SBR Tg PLA point on curve E′ = f(T)) (° C.) (° C.) CP3 −68 51 CP4 −67 / CP2 −48 53 Control mixture −60 /

[0246] A significant drop in E′ at the Tg of the elastomer is noted. A rubbery plateau appears quite clearly for the copolymers over a temperature range [−20° C., 90° C]. In comparison, the SBR/PLA control mixture also exhibits a rubbery plateau, but its temperature range is more restricted [−20° C., 20° C].

EXAMPLE 2

SBR-g-PLA Comb Copolymers Obtained by Polymerization of Lactide on an Alcohol-Functionalized SBR by Reactive Extrusion

[0247] Copolymers of comb type (SBR-g-PLA) were synthesized by polymerization of the lactide, in the presence of a functional SBR having mercapto 1-butanol groups grafted along the chain.

[0248] This functional SBR is prepared according to the following procedure.

[0249] Grafting:

[0250] After complete dissolution of 110 g of SBR in 2.75 l of methylcyclohexane, 6.3 ml of 4-mercaptobutanol, dissolved beforehand in 135 ml of dichloromethane, are added. Once the temperature of the reaction medium is at 80° C., 1 g of lauroyl peroxide dissolved in 50 ml of methylcyclohexane is introduced with stirring. The medium is kept at 80° C. with stirring overnight.

[0251] At 80° C., 2 equivalents, relative to the peroxide, of Irganox® 2246 are added. After 15 minutes, 2 equivalents, relative to the peroxide, of 6-PPD are added. After cooling, one or two coagulations in methanol are carried out.

[0252] The functionalized elastomer is then redissolved, and 0.4% by weight, relative to the weight of the elastomer, of an Irganox®2246/6PPD (80/20) mixture is added. The functionalized elastomer is then dried under vacuum at 50° C.

[0253] Results:

[0254] The grafting obtained is 1.3 mol %, and the yield by mass obtained is 82%.

[0255] The microstructures and macrostructures of this functionalized SBR are given in the following table:

TABLE-US-00007 TABLE 7 Macrostructure Microstructure Mn (g/mol) PI % 1,4-PB % 1,2-PB % PS % OH 204 700 1.3 19.7 62.2 16.8 1.3

[0256] Polymerization conditions: the synthesis was carried out in a microextruder in accordance with the experimental protocol described in Example 1, P2 (sequenced addition). The various operating conditions tested are reported in the following table:

TABLE-US-00008 TABLE 8 SBR/LA [LA/Sn(oct).sub.2] [SBR/Sn(oct).sub.2] Sn/P U626 (% (g/g) mol mass mol total mass.) CP′1 60/40 700 373 1/1 0.07%

[0257] For the comb copolymer obtained (CP′1), it is observed on the .sup.1H NMR spectra that the signal at 3.64 ppm has disappeared. Consequently, all the —S—(CH.sub.2).sub.4—OH functions have initiated the polymerization of the lactide.

[0258] The results are reported in the following table:

TABLE-US-00009 TABLE 9 Conversion Mn triblock Fin comp % by .sup.1H Time Mn PLA.sup.1 (g/mol) PI SBR/PLA (mass) NMR (min) block (g/mol) SEC triblock .sup.1H NMR CP'1 91.1% 5 2200 229 400 2.1 63/37 .sup.1Mn of each block calculated by the following formula: [00002]$M_n^{\mathrm{PLA}\mathrm{block}}=\frac{1}{\mathrm{Number}\mathrm{of}\mathrm{OH}\mathrm{functions}\mathrm{per}\mathrm{chain}}.Math.\frac{M_n^{\mathrm{SBR},\mathrm{SE}C\mathrm{eq}.\mathrm{PS}}}{1-\%{\mathrm{massPLA}}^{\mathrm{NMR}}}.Math.\%{\mathrm{massPLA}}^{\mathrm{NMR}}$

[0259] Tensile Tests

[0260] The results are reported in the following table:

TABLE-US-00010 TABLE 10 TENSILE FORCE Tensile strength (MPa) Elongation at break (%) CP′1 11.8 440

[0261] The results of the tensile tests show: [0262] a mean elongation at break of 440% [0263] a mean tensile strength of 11.8 MPa

[0264] DMA

[0265] The results of the DMA tests show: [0266] the appearance of a rubbery plateau [0267] the range of temperature resistance up to 60° C.

EXAMPLE 3

PLA-SBR-PLA Triblock Copolymers Obtained by Polymerization of Lactide on an Amine-Functional SBR by Reactive Extrusion—Continuous Process

[0268] The tests were also carried out in a twin-screw extruder, having an L/D ratio of 56 and comprising 14 independent heating zones (L/D=4), allowing a continuous synthesis. The rotational speed of the screws is 70 rpm. The setpoint temperatures of the barrels are reported in the following table:

TABLE-US-00011 TABLE 11 Barrel temperatures (° C.) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 50 80 180 180 180 180 180 180 180 180 180 180 180 180

[0269] The aromatic primary amine-difunctionalized SBR was synthesized according to the protocol given in Example 1.

[0270] The microstructures and macrostructures of this difunctionalized SBR are given in the following table:

TABLE-US-00012 TABLE 12 Macrostructure Microstructure Mn (g/mol) PI % 1,4-PB % 1,2-PB % PS 87 300 1.1 32.0 44.0 24.1

[0271] This SBR is dried for 12 h at 60° C. in air.

[0272] The lactide is introduced into barrel No. 1, the functionalized SBR (as a mixture with 2% by weight of EVA) is introduced into barrel 2 and the catalytic system is introduced into barrel 3. The SBR/lactide ratio by mass is 60/40. The [LA/Sn(oct).sub.2] molar ratio is 700, and P(Ph).sub.3 is added in an amount which makes it possible to have an (Sn/P) molar ratio of 1/1. The conversions and the properties of the copolymer obtained are reported in the following table:

TABLE-US-00013 TABLE 13 Mechanical Conversion Fin comp Triblock properties % by SBR/PLA macrostructure Tensile Strain at .sup.1H Time Mn PLA (mass) .sup.1H Mn strength break RMN (min) (g/mol).sup.1 NMR (g/mol) PI (MPa) (%) 91 8.4 23 500 80/20 108 800 3.0 2.0 160 .sup.1Mn of each PLA block calculated by the following formula: [00003]$M_n^{\mathrm{PLA}\mathrm{block}}=\frac{1}{2}.Math.\frac{M_n^{\mathrm{SBR},\mathrm{SE}C\mathrm{eq}.\mathrm{PS}}}{1-\%{\mathrm{massPLA}}^{\mathrm{NMR}}}.Math.\%{\mathrm{massPLA}}^{\mathrm{NMR}}$