WO1997041160A1

WO1997041160A1 - Alkyl methacrylate polymers

Info

Publication number: WO1997041160A1
Application number: PCT/GB1997/001128
Authority: WO
Inventors: Jianming Yu; Noel Overbergh; John Michael Hudson; Phillip James Hammond
Original assignee: N V Raychem S A; Raychem Limited
Priority date: 1996-04-26
Filing date: 1997-04-24
Publication date: 1997-11-06

Abstract

M-A-M triblock copolymers of higher alkyl (especially isobornyl) methacrylates, potentially for forming gels of improved temperature rating over PMMA triblock gels, are synthesized by anionic polymerization of an alkylene (pref. butadiene or isoprene) mid-block (A) followed by anionic polymerization of the methacrylate end blocks (M) using alkali metal alkyl initiators. Mixed end blocks (M) comprising random or block copolymers of methylmethacrylate and one or more higher alkyl (pref. isobornyl) methacrylates are preferred for forming gels with elevated softening temperatures without loss of structure which apparently tends to occur with IBMA homopolymer ends blocks.

Description

AI.KYL MKTΗACRYΪΛTE POLYMERS

This invention relates to alkyl methacrylate polymers and synthesis thereof.

Triblock copolymers of t-butylmethacrylate-isoprene-t-butylmethacrylate are known, for example from EP-A-0431706, in which it is disclosed that the alkyl group of the methacrylate blocks may have from 1 to 14 carbon atoms, preferably up to 8 carbon atoms.

The present invention provides a novel alkylmemacrylate homopolymer, novel random and diblock alkylmethacrylate copolymers, and novel alkylmethacrylate triblock copolymers incoφorating blocks of the said novel homopolymer or random or diblock copolymers, which may have advantageous characteristics in themselves, and may be especially useful for forming gels with differences or advantages over those based on corresponding methylmethacrylate triblocks described in our co-pending British Patent Application No.9512125.7 (RK509).

A first aspect of the present invention accordingly provides synthesis of poly- isobornylmethacrylate (PIBMA) comprising anionic polymerisation of isobomyl methacrylate at a temperature up to 40°C, preferably within the range from -78 to 40°C, more preferably within the range from 0 to 30^CC, especially preferably within the range from 10 to 25 °C.

It has unexpectedly been found that this polymerisation may be effected at relatively convenient temperatures using sterically unhindered initiators such as trimethylsilylmethyl lithium, whereas the known anionic polymerisation of methylmethacrylate must be conducted at less than -60°C using a sterically hindered initiator such as l ,l'-diphenyl-3,3'-dimethylbutyl lithium to obtain a satisfactorily narrow range of molecular weights in the polymer product.

A second aspect of the invention provides synthesis of a diblock or multiblock copolymer of (a) methylmethacrylate and (b) a C₂ (preferably C₄)-or-higher alkyl (preferably isobomyl) methacrylate comprising anionic polymerisation of either (a) or (b) to form a living polymer, followed by addition and anionic polymerisation of the other monomer (b) or (a), the polymerisation of (b) being conducted under conditions specified above for the first aspect of this invention, and the polymerisation of (a) being conducted at a temperature lower than -40°C, preferably lower than -60°C.

A third aspect of the invention provides synthesis of a random copolymer of (a) methylmethacrylate and (b) a C₂ (preferably C₄)-or-higher alkyl (preferably isobomyl) methacrylate comprising anionic polymerisation of a mixture of the respective monomers at a temperature lower than -40°C, preferably lower than -60°C.

These random and block copolymers, preferably consisting substantially only of the said components (a) and (b), can be made to provide unique combinations of properties derived from the respective monomers, the mol. proportions of the methylmethacrylate to the C₂ (preferably C₄)-or-higher alkyl methacrylate preferably being within the range from 5:95 to 95:5, more preferably 30:70 to 70:30. These random and diblock copolymers may be especially useful as end blocks in gel-forming methacrylate triblock copolymers, as described in the aforementioned co-pending application. Some or all of the methylmethacrylate component (a) may be replaced by a C₂ (preferably C₄)-or- higher alkyl methacrylate other than that chosen for component (b), and the invention accordingly includes a diblock, multiblock, or random copolymer (i) of methylmethacrylate and a C₂ (preferably C₄)-or-higher alkyl (preferably isobomyl) methacrylate, or (ii) of two or more C₂ (preferably C₄)-or-higher alkyl methacrylates with or without methy methacrylate.

A fourth aspect of the present invention accordingly provides synthesis of an alkylmethacrylate-alkylene-alkylmethacrylate triblock copolymer, comprising (i) polymerisation of an alkylene monomer (preferably butadiene or isoprene) in a substantially apolar solvent (preferably cyclohexane and/or toluene), preferably with added more polar solvent (preferably diethyl ether), to form a difunctional living polyalkylene block, followed by anionic polymerisation, in the presence of that polyalkylene block, of an alkylmethacrylate by a method according to any of the above first, second, and third aspects of the present invention. General methods, materials and conditions for performing this triblock synthesis according to the fourth aspect of the present invention may be adapted, for example, from those described in the aforementioned EP-A-0431706, using conventional alkali metal alkyl di-functional initiators such as sec-butyl lithium or preferably ten-butyl lithium with l,3-bis(l-phenylethenyl)benzene or with meta-di-isopropenylbenzene (m-DIB) as described for example by Ladd and Hogan-Esch in Polym. Prepr. , 2Q (1), 261 , 1989, in cyclohexane/diethylether mixed reaction solvent. Preferably, the polymerisation of the alkylene monomer for mid-block of the triblock synthesis will use a difunctional alkali metal alkyl initiator, such as difunctional l,3-phenylene-bis(3,3-dimethylpentylidene)di- lithium. It is preferred to use for the polymerisation of the alkylmethacrylate end blocks a difunctional alkali metal initiator, for example difunctional l,3-phenylene-bis(3,3- dimethylpentylidene)di-lithium. For synthesis of the methacrylate homopolymer and random or block methacrylate copolymers, mono-functional initiators may also be used, for example sec- or tert-butyl lithium reacted with diphenylethylene.

The triblock synthesis will preferably include the additional step of hydrogenating the polyalkylene block. The hydrogenation step converts the preferred polybutadiene or polyisoprene mid-block to ethylene/butylene or ethylene/propylene respectively, and mixed mid-blocks containing both may also be used.

In all of the syntheses according to this invention, it may be preferred that anionic polymerisation of the alkymethacrylate is effected in the presence of a polar solvent, preferably comprising tetrahydrofuran (THF), preferably in a mixture with substantially apolar solvent, preferably toluene or cyclohexane. The mixture of polar and apolar solvents has been found advantageously to narrow the molecular weight range of the resulting polymers and may be used to vary their tacticity, for example from 60% syndiotactic PIBMA in THF to 65% isotactic PIBMA in toluene, both at -78°C.

Other aspects of the present invention provide: (a) anionically polymerised isobornylmethacrylate; (b) a diblock, multiblock, or random copolymer of methylmethacrylate and a C₂ (preferably C₄)-or-higher alkyl (preferably isobomyl) methacrylate; and (c) an alkylmethacrylate-alkylene-alkylmethacrylate triblock copolymer wherein at least some of the alkyl groups of the alkylmethacrylate blocks comprise C₂ (preferably C₄)-or-higher (preferably isobomyl) alkyl groups. These novel block copolymers will preferably be the product of anionic polymerisation, preferably using a mono-functional alkali metal alkyl initiator, for example l , l-diphenyl-3,3-dimethyl-butyl lithium, preferably in the presence of a polar solvent.

The alkylene mid-blocks of the triblock copolymers will preferably comprise polyisoprene, polybutadiene, more preferably poly(ethylene/butylene) and/or poly(ethylene/propylene). The alkylmethacrylate blocks of the triblock copolymers will preferably comprise diblock, multiblock, or random copolymers of methylmethacrylate and a C₂ (preferably C₄)-or-higher alkyl (preferably isobomyl) methacrylate. The number average molecular weight Mn of the triblock copolymers for some purposes is preferably within the range 40,000 - 300,000, the methacrylate end blocks preferably having Mn within the range 6000 - 70,000, and the alkylene mid-blocks perferably having Mn within the range 30,000 - 160,000. However, these or other molecular weights will be selected to suit the desired end use of the polymers, for example for making gels.

The various aspects of the present invention will now be further illustrated by the following specific examples using isobornylmethacrylate. Materials and conditions for these were generally as follows:

A. Materials preparation:

Methylmethacrylate (MMA) from Aldrich and isobornylmethacrylate (IBMA) from Acros Chimica were first refluxed over CaH₂ under a nitrogen atmosphere. They were then distilled under vacuum and stored under nitrogen at -20°C. Just before polymerization, the IBMA was added at -78 °C to a 50/50 v/v mixture of diisobutyl aluminium hydride (DIB AH: 0.1N in toluene) and triethylaluminium (TEA: 0.1 N in toluene) until a persistent yellowish-green colour was observed, whereas MMA was added at room temperature to TEA solution. They were then redistilled under reduced pressure and polymerized.

LiCl (99.99% purity from Aldrich) was dried overnight at 130°C and dissolved in dry THF (0.5N solution). Cyclohexane and diethyl ether were dried over CaH₂ for 24 hours. THF was purified by refluxing over the deep puφle sodium-benzophenone complex . All the solvents were further distilled from polystyryllithium under reduced pressure immediately before use. Tert-butyllithium (t-BuLi) from Aldrich (1.3M in cyclohexane) was diluted with cyclohexane into a 0.248N solution as determined by double titration. Meta-diisopropenylbenzene (m-DIB) from Aldrich was first distilled over CaH₂ for 24 hours and then from fluorenyllithium before use. 1 ,1-diphenyl ethylene (DPE) from Aldrich was dried over sec-BuLi and distilled from diphenylmethyllithium before use. Butadiene was dried over n-BuLi.

B. Initiators l ,l-diphenyl-3,3-dimethyl-butyl lithim (DDBLi) was used as a monofunctional initiator and prepared by addition of t-BuLi to DPE (diadduct). The t-BuLi/m-DIB diadduct was prepared in cylohexane at 50 °C for 3 hours and used as a difunctional initiator. Solutions of these mono- and di-functional initiators were homogenous with a deep red color.

C. Polymerization

Homopolymerization of IBMA and block copolymerization of butadiene and IBMA were carried out in glass reactor equipped with a magnetic stirrer under an inert atmosphere. Solvent, initiator and monomers were transferred with a syringe and/or capillaries. Details for the experimental techniques used in the synthesis of triblock copolymers were similar to those hereinbefore described. Briefly, the synthesis consisted of 3 steps: 1) butadiene was polymerized in a cyclohexane/diethyl ether mixture (100/6, v/v) at room temperature for one night; 2) PBD dianions were end-capped with diphenylethylene (DPE) at room temperature for 30 minutes; 3) THF was added at 0°C so that a mixture of cyclohexane/THF (50/50, v/v) was prepared, to which IBMA was finally added and polmerized at either low or room temperature. Triblock copolymers were recovered by precipitation in methanol and dried at room temperature for 2 days in vacuum. D. Hydrogenation

An alkyl metal/transition metal salt complex was used as homogeneous hydrogenation catalyst. The metal alkyl was triethyl aluminium (1 N in toluene) and the metal salt was cobalt 2-ethyl hexanoate (0.2 N in toluene). The catalyst complex was prepare by adding dropwise the transition metal salt to the metal alkyl in toluene under nitrogen. The molar ratio of component metals (alkyl/salt) was 3/1. Hydrogenation was conducted in a 5-litre autoclave equipped with a mechanical stirrer. A solution of 20 g of block copolymer in 3 1 dry toluene was firstly mixed with the catalyst complex (about 0.03 moles of transition metal per mole of double bonds) and injected, and the reactor was closed and purged with nitrogen. The reactor was heated to 60°C, purged with hydrogen, hydrogen pressure was increased to 6 bar and the reaction allowed to proceed for approximately 3 hours. After hydrogenation, the catalyst was decomposed with dilute HCl . The copolymer was preciptated in methanol, washed and redissolved in toluene, reprecipitated and dried under vacuum.

E. Film preparation

Block copolymers were added with lwt% hindered phenol antioxidant (tetrakis [methylene 3-(3 ^' ,5 ^'-di-t-butyl-4 '-hydroxylphenyl) propionate] methane. Irganox 1010 Trade Mark from Ciba-Geigy Coφ.) and dissolved in toluene. This solution (8wt% copolymer) was poured into a Petri dish and the solvent was allowed to evaporate slowly over 3 to 4 days at room temperature. Films were dried to constant weight in a vacuum oven at 40°C. They were elastomeric, transparent and colourless with a smooth surface.

F. Analysis

Molecular weight and molecular weight distribution were measured by size exclusion chromatography (SEC) with a Waters GPC 501 apparams equipped with linear styragel columns. THF was the eluent (flow rate of 1 ml/min) and polystyrene (PS) standards were used for calibration. The method by Benoit et al for the universal calibration was used with the following viscosimetric relationship: [η] = 1.36x10 α (PS in THF) [η] = 3.65xl0^"5 α^{0 730} (PIBMA in THF). H NMR spectra were recorded with a Brucker AN-400 spectrometer, by using CDC1₃ as a solvent. Content of the PBD 1 ,2-units was calculated by Η NMR from the relative intensity of the signal at 4.9 ppm (CH = : 1,2 double bond), 5.4 ppm (CH = : 1,2 plusl ,4 double bond). Tacticity of PIBMA was calculated by quantitive ¹³C NMR. Composition of the copolymer was calculated by IH NMR from the signal for the 1,2 units of PBD and signal at 4.4 ppm for the O-CH of the IBMA units. Mn for PIBMA was calculated from composition and PBD molecular weight. IR spectra were recorded with the 600 FT-IR Perkin-Elmer spectrometer.

Differential scanning calorimetry (DSC) was carried out with a DuPont 900 instrument , calibrated with indium. The heating rate was 20°C/min, and glass transition temperature was reported as the inflection point of the heat capacity jump. Width of glass transition (Tg) was defined as the difference in the temperatures of the intersections of the tangent to the heat capcity curve at Tg with the extrapolated baselines.

Dynamic Mechanical Analysis (DMA) was carried out with a TA 983 Dynamic Mechanical Analyser (du Pont). Samples (8x10x2 mm) were deformed at constant frequency (1Hz) and strain amplitude (0.4 mm).

Tensile measurements were conducted with a Adharmal Lomargy tensile tester. Testing samples (microdumbells) cut from solution cast films was extended at 200 mm/min at room temperature. Reported data are the average of three measurements.

Example 1 - Synthesis of polyisobornyl methacrylate (PIBMA)

1 ml t-BuLi was added to 40ml THF containing 3 ml DPE solution (0.392N) in cyclohexane and 2ml LiCl solution at 0°C. The solution was then brought to the reaction temperature (from -78 to 40° C), 3 ml of IBMA was added and allowed to polymerize for about 1 hour. Polymer was recovered by precipitation in 200ml methanol. Note: here the reaction product of t-BuLi and DPE, that is l,l-diphenyl-3,3-dimethylbutyl lithium (DDBLi), was used as an iniiator. As an alternative example, trimethylsilyl-methyllithium ((Me)₃SiCH₂Li) was used to directly polymerize IBMA without reacting with DPE. PIBMA of Mn as high as 100,000 with very narrow molecular weight range ( < 1.15) was obtained at temperature from -78 to 25 °C. This is very interesting, since PMMA of narrow Mn distribution can only be obtained at temperature lower than -60°C by usual anionic polymerization techniques, even with sterically hindered initiator, such as DDBLi, whereas trimethylsilymethyllithium is not very sterically hindered and still produces PIBMA of very narrow Mn distribution at room temperature.

Monomer purification is a key issue in living polymerization of methacrylate esters. In case of branched alkyl methacrylate, the present branched alcohol is the main impurity, whose complete elimination is a problem compared to the normal equivalent because of a lower reactivity toward triethyl aluminium (TEA). An efficient purification technique has been proposed and applied to t-butyl methacrylate (tBMA), that consists of the addition of diisobutyl aluminium hydride (DIBAH) to the TEA solution. This method has been successfully used for the purification of isobomyl methacrylate (IBMA) in the present invention, since polymerization of accordingly purified IBMA provides a polymer of a narrow molecular weight distribution ( < 1.25) in THF as shown in Table 1. Nevertheless IBMA must be separated from the DIBAH/TEA mixture by distillation prior to polymerization. The high boiling point of IBMA (245°C/760 mm Hg) is responsible for the partial polymerization even when distillation is conducted at 110°C under reduced pressure. In order to avoid that drawback, IBMA has been tentatively polymerized in the presence of the residual DIBAH/TEA mixture. Table 1 shows that samples P3 and P8 that have been prepared with the non-distilled monomer do not significantly differ from the PI and P4 samples prepared with IBMA previously distilled.

It is worth noting that initiation of the IBMA polymerization by DDBLI in THF and in toluene is slower compared to MMA. Indeed, the red color of the initiator does not disappear immediately but slowly when the monomer is added, in shaφ contrast to what happens when MMA is the monomer.

In samples PI and P2, molecular weight, molecular weight distribution, monomer conversion and Tg are the same although the polymerization temperature is very different, i.e. -78°C for PI and 0°C for P2. Although PIBMA prepared in THF (PI to P3 samples) has a rather narrow molecular weight distribution (1.25), a small tail is observed on the low molecular weight side. The anionic polymerization of IBMA has been repeated in THF in the presence of LiCl "ligand" with a LiCl/initiator molar ratio of 5. Table 1 shows that the molecular weight distribution becomes narrower (1.05), and spectra confirm that the low molecular weight tail has disappeared. When the polymerization temperature is increased from -78 °C to 40 °C (samples P4 to P7 in Table 1), the molecular weight distribution is slightly increased from 1.05 to 1.15 and the experimental molecular weight remains in a good agreement with the theoretical value. Nevertheless, the chain tacticity is affected, since syndiotacticity of PIBMA is decreased from 70% to 50% at die expense of the hetero triads. Thus compared to the anionic polymerization of MMA, which is adversely affected by the polymerization exotherm ( > 10°C) at -78°C, no side reaction occurs in the course of the anionic polymerization of IBMA in a large temperamre range. So a careful control of the reaction exotherm is not required.

In addition to polymerization temperature and ligand, solvent polarity also affects the polymer tacticity and the "livingness" of polymerization. The stereochemical addition of the incoming monomer to the propagating enolate is indeed strongly dependent on the presence or absence of peripheral solvation. Table 1 reports polymerization experiments not only in THF, but also in apolar solvents such as toluene and cyclohexane, and 9/1 (v/v) mixture of these solvents and THF in which LiCl has a limited solubility compared to complete insolubility in pure apolar solvent. Similarly to tBMA, polymerization of IBMA is not "living" in an apolar solvent at room temperature and a broad molecular weight distribution is observed, 2.25 in toluene and 5.05 in cyclohexane, as shown in Table 1. This situation is however significantly improved by addition of 10% THF, since the molecular weight distribution dramatically decreases down to 1.25 in the 9/l(v/v) toluene/THF mixmre and to 1.20 in the cyclohexane/THF mixmre of the same composition. The effect of solvent polarity on chain tacticity in synthesis at 25°C is clearly illustrated by comparison in Table 1 of sample P6 (55% syndiotactic triads in THF), sample P9 (65% isotactic triads in toluene), and sample P10 (37% syndiotactic triads in toluene/THF 9/1 v/v). Thus, combination of a polar and an apolar solvent allows control of tacticity over a wide range. The glass transition temperamre (Tg) of PIBMA homopolymer (see Table 1) ranges from 174°C to 206 °C depending on the chain tacticity. These values are in good agreement with Tg of PIBMA of comparable tacticity synthesized by a radical process.

Table 1. Polymerization of isobomyl methacrylate (IBMA) with 1 , 1-dipheny 1-3,3- dimethyl-butyl lithium (DDBLi) as an initiator sample solvent ligand reactn reactn yield Mn cal Mn Mw / (% ιmicro Tg* time temp (%)^c SEC^e Mn structure/ (°C

(hours (°C) s h i )

)

Pi THF -78 100 14700 19000 1.25 66 34 0 196

P2 THF 100 14700 16000 1.25 58 39 3 199

P3" THF -78 100 19800 27000 1.30 74 26 0 206

P4 THF LiCl -78 78 12000 19000 1.05 70 27 3 202

P5 THF LiCl 83 12000 19000 1.05 61 37 2 195

P6 THF LiCl 25 91 13000 19000 1.15 55 43 2 198

P7 THF LiCl 40 93 13000 19000 1.15 50 45 5 196

P8" THF LiCl -78 90 13000 19000 1.05 73 27 0 197

P9 Toi 12 25 100 29000 72000 2.25 2 33 65 174

P10 Tol/TH LiCl 1.5 25 100 29000 26000 1.25 37 41 22 194 F

Pl l CH 12 25 80 29000 33000 5.05 8 32 60 177

P12 CH/TH LiCl 1.5 25 83 29000 31000 1.20 34 46 20 192 F ^aTol=toluene, Tol/THF=toluene/THF(9/l v/v), CH= cyclohexane,

CH/THF=cyclohexane/THF(9/l v/v); ^bLigand: Initiator mol ratio = 5; ^cRatio of recovered polymer weight to charged materials weight; ^dCharged monomer weight divided by initiator molar number for living polymerisation; ^eBased on polystyrene calibration and accordingly calculated; ^fNMR ^I3C; ^εby DSC, heating rate 20°C/min; ^hmonomer added together with residues of DIBAH/Et₃Al purification agents. Example 2 - Block copolymerization of MMA and IBMA lml t-BuLi was added to a mixmre of 40ml THF containing 3 ml DPE solution (0.392N) in cyclohexane and 2ml LiCl solution at 0°C. The solution was then brought to - 78°C, and 3ml MMA was added and polymerized for 1 hour. An aliquot was taken out for SEC analysis in order to determine the Mn of PMMA sequence. 3 ml of IBMA was then added and allowed to polymerize for 1 hour. Copolymer was recovered by precipitation in 200 ml methanol.

Example 3 - Random copolymerization of MMA and IBMA

2 ml t-BuLi was added to a mixmre of 60 ml THF and 4 ml LiCl solution containing 4 ml DPE solution (0.392N) in cyclohexane at 0°C. The solution was then brought to -78 °C, and a mixmre of MMA (3 ml) and IBMA (3 ml) was then added and allowed to polymerize for 1 hour. Copolymer was recovered by precipitation in 200 ml methanol.

The properties of the copolymers produced by Examples 2 and 3 are shown in Table 2.

Table 2. Block and random copolymerization of MMA and IBMA

Recovered polymer weight to charged monomer weight; ^dby SEC with PS for calibration; ^eDSC heating rate is 20°C/min. Example 4 - Synthesis of IBMA-butadiene(B)-IBMA triblock copolymer

A. Preparation of Difunctional Lithium Initiator (DLI).

11ml t-BuLi solution (0.248N) in cyclohexane was mixed with 14ml m-DIB solution (0.0839N) in cyclohexane at room temperamre and was reacted at 50°C for 2 hours.

B. Polymerisation of butadiene.

6ml DLI was added to a mixmre of cyclohexane/diethyl ether (250ml/20ml). 20ml butadiene was then added at 0°C and polymerized at room temperamre for 12 hours.

C. Polymerisation of IBMA.

7ml DPE solution (0.392N) in cyclohexane was added to the mixmre resulting from step B at room temperamre, then 300 ml THF containing 3ml LiCl solution was added at 0°C and the mixmre was brought to the reaction temperamre. Then 7ml IBMA was added and polymerized for 2 hours. Copolymer was recovered by precipitation in 21 of methanol. Alternative samples were conducted at reaction temperamres of -78 °C, or 25 °C, and copolymers of narrow Mn distribution ( < 1.10) were obtained even at 25 °C, which exhibited high strength (tensile strength > 30MPa, elongation at break > 1000%).

Synthesis of well defined PMMA-PBD-PMMA (MBM) triblock copolymers is achieved by using the m-DIB/t-BuLi diadduct as a difunctional initiator for the butadiene polymerization. Table 3 (synthesis conditions) and Table 4 (thermal and mechanical properties) show that this technique is also successful in preparation of triblock copolymer in which PIBMA is substimted for PMMA. Typical SEC traces show an identical symmetrical, very narrow molecular weight distribution for both PBD midblock and the triblock copolymer (1.10), which indicates that the polybutadienyl dianions end-capped by DPE quantitatively initiate polymerisation of the IBMA. A major advantage of IBMA over MMA is that copolymerization of the methacrylic monomer can be conducted at 25 °C, instead of -78°C, while keeping intact the control on the molecular structure of the triblock. The C3 sample synthesised at 25 °C has indeed the same molecular weight characteristics as the Cl sample prepared at -78 °C for the IBMA polymerization. As in case of IBMA homopolymerization, the use of IBMA containing the purification agents (DIBAH/TEA mixmre) (Sample C2) rather than the corresponding distilled monomer (samples Cl and C3) does not perturb the copolymerization course. In all cases, a very narrow molecular weight distribution is observed (1.10). It is worth pointing out that no gelation occurs upon addition and polymerization of IBMA even at -78 °C in cyclohexane/THF(60/40, v/v) at a 7wt% polymer concentration, although in case of MMA, a gel is immediately formed when the monomer is added to a 50/50(v/v) cyclohexane/THF at a 3wt% polymer concentration. Thus a smaller THF content, a higher polymerization concentration and a much higher polymerization temperamre compared to MMA make the PIBMA-PBD-PIBMA triblock copolymers very promising materials for industrial production.

In order to illustrate the range of end products that can be made available by living block copolymerization of IBMA, a the triblock copolymer of sample Cl was hydrogenated (sample CIH, Table 4) by methods generally indicated hereinbefore using a Co/Al catalyst. FTIR and Η NMR analysis confirm the quantitative conversion of the PBD to the saturated counteφart which is much more resistant to oxidation and better suited to high temperamre applications. Spectra show the IR absoφtions at 960 and 910 cm^"1 for 1 ,4 and 1,2-units respectively, and at 1640 cm^"1 for the C=C stretching have disappeared, in contrast to the absoφtion of PIBMA at 1725 cm^" which remains unchanged after hydrogenation, although this polymethacrylate is known for propensity to hydrolyse in the presence of an acid. SEC analysis shows the molecular weight distribution remains narrow: 1.15 instead of 1.10 before hydogenation. A small shoulder on the high molecular weight side of the elution peak is however detected, the origin of which is still unclear.

From the DSC trace of toluene cast films of triblock copolymers, Tg of the polybutadiene block is clearly observed at ca. -60 °C, independently of the hard block PMMA or PIBMA. The hydrogenated sample (CIH) shows an ethylene/butylene (E/B) block of very broad and ill-defined melting endotherm with a very diffuse maximum at ca. -7°C, which indicates that the E/B central block tends to crystallize with formation of poorly organized crystalline phases, as has been observed for known styrene-ethylene/butylene- styrene (SEBS) triblock copolymers. Table 3. Synthesis of AMA-B-AMA triblock copolymers with m-diisopropenyl benzene(m-DIB)/t-BuLi as an difunctional initiator sample PAMA T yield PBP Mw/Mn (°C)^a (%)^b PAMA

Mn. lO^"3 Mn. lO^"3 1,2 Mw/Mn ^d Mn ^f cont^e cal.^c SEC^d (%)

Cl PIBMA -78 100 50 60 43 1.10 2x15000 33 1.10

C2^g PIBMA -78 100 50 60 45 1.10 2x15000 33 1.10

C3 PIBMA 25 100 50 60 43 1.10 2x15000 33 1.10

M PMMA -78 100 50 60 43 1.10 2x16000 34 1.10

polymerization temperamre for methacrylate monomer; weight ratio of recovered polymer to charged monomers; ^c calculated as the ratio of monomer weight to molar number of initiator; ^d SEC with PS calibration; ^e ' H NMR analysis; ^f Mn was calculated from the copolymer composition and the PBD molecular weight; ^£ IBMA monomer was purified with no distillation.

Table 4. Thermal and mechanical properties of PIBMA-PBD-PIBMA and MBM triblock copolymers

^a DSC heating rate 20°C/min, values in parentheses by DMA at 1Hz with heating rate 5°C/min; ^b ratio of the unrecoverable deformation to initial sample length at break. Example 5 - Synthesis of I/M-B-I/M and I-M-B-I-M triblock copolymers.

I/M represents a random copolymer of IBMA and MMA. I-M represents a block copolymer of IBMA and MMA. The preparation of DLI and polymerization of butadiene are the same as in the Example 4 synthesis of IBI triblock copolymers. Co-polymerisation of MMA and IBMA with pre-existing butadiene block was effected as follows. First, 7ml DPE solution (0.392N) in cyclohexane was added to the butadiene polymerisation mixmre at room temperamre; then 300 ml THF containing 3 ml LiCl solution was added at 0°C and this intermediate mixmre was then brought to -78 °C.

For I/M-B-I/M, a mixmre of IBMA (3ml) and MMA (3ml) was added to the above intermediate mixmre and polymerized for 2 hours. Copolymer was recovered by precipitation in 21 methanol.

For I-M-B-I-M, 3ml MMA was added to the intermediate mixmre and polymerized for 1 hour. Then 3 ml IBMA was added and polymerized for another 1 hour. Copolymer was recovered by precipitation in 21 methanol. The properties of the mixed methacrylate triblocks produced are shown in Table 5.

Table 5. Synthesis and properties of mixed methacrylate triblock copolymers

SAM END Tg PBD composition Mw/M Tensile properties (25°C) c

PLE BLK CO n^e

Mn Mn 1,2% B M I T.S.(MPa EB(%) Set(% cal^b sec^c d ) )

Mc24a I/M -58 46000 56000 42 66 17 1 1.10 24 1010 50

7

Mc24b I/M -56 46000 60000 42 66 24 1 1.10 27 996 50 0

Mc33a I-M -58 46000 56000 43 67 16 1 1.10 30 1130 38

7

Mc33b I-M 46000 56000 41 66 10 2 1.10 30 1100 33 4 ^aI=IBMA, M=MMA, B=butadiene; ratio of charged monomer to molar number of initiator; with PS for calibration; d 1 H NMR; from charged monomer weights; T.S. =Tensile Strength, EB=Elongation at Break, set=permanent set at break calculated as ratio of irreversible deformation at break to initial length of sample.

Example 6. Ethylmethacrylate-Butadiene-Ethylmethacrylate Triblock Copolymer

When synthesised by methods similar to those known for corresponding methylmethacrylate triblocks at block molecular weights (Mn x IO^"3) of 13-59-13 and 1,2% of 41 , the above EMA-B-EMA triblocks displayed at room temperamre relatively high tensile strength of 19 MPa and elongation at break of 1130%, which may provide useful properties when EMA is combined with MMA in the mixed methacrylate copolymers according to the present invention hereinbefore described. However, the Tg of the ethylmethacrylate blocks is relatively low, e.g. about 80°C, and the higher alkyl (preferably C₄-or-higher alkyl, especially isobomyl) methacrylates may therefore be preferred for the mixed methacrylate diblock and triblock copolymers.

Example 7: MMA-Styrene-Butadiene-Styrene-MMA Pentablock

By methods corresponding to those hereinbefore described, sequential living anionic polymerisation of butadiene (B), styrene (S), and methylmethacrylate was performed to produce an M-S-B-S-M pentablock copolymer (A6) and its hydrogenated derivative M-S- EB-S-M (A6H) having properties shown in the following Table.

Sample Mn^a xl0^"; PBD" PMMA Tgl^c Tg2^c

(wt%) 1,2(%) (wt%) co (°C)

A6 19-18-79-18-19(153) 52 43 24 -60 (-55) 110 (130)

A6H Mw/Mn = 1.20 -50 (-49) 112 (128) ^aby SEC and 'H NMR, total Mn in brackets; "by 'H NMR; ^c by DSC at 20°C/minute heating rate (by DMA at 1Hz in brackets); ^dby SEC with polystyrene calibration standards. It has furthermore been suφrisingly found, according to the present invention, that the IBMA/MMA pentablock copolymers can be conveniently synthesised at 0°C with increased yield and Tg and narrower molecular weight distribution, at least up to a MMA content of 1/3 by weight based on the combined weight of MMA and IBMA, whereas the triblock copolymers of MMA alone must be synthesised at much lower temperamres. In addition, the presence of the IBMA has been found to reduce gelling of the reaction mixmre during polymerisation, so that the concentration of the reaction mixmre can advantageously be increased compared with the MMA-only triblock reaction mixmres.

Claims

1. Synthesis of poly-isobornylmethacrylate (PIBMA) comprising anionic polymerisation of isobomyl methacrylate at a temperamre up to 40°C, preferably within the range from -78 to 40°C, more preferably within the range from 0 to 30°C, especially preferably within the range from 10 to 25 °C.

2. Synthesis of a diblock or multiblock copolymer of (a) methylmethacrylate and (b) a C₂ (preferably C₄)-or-higher alkyl (preferably isobornyl) methacrylate, comprising anionic polymerisation of either (a) or (b) to form a living polymer, followed by addition and anionic polymerisation of the other monomer (b) or (a), the polymerisation of (b) being conducted according to claim 1, and the polymerisation of (a) being conducted at a temperamre lower than -40°C, preferably lower than -60°C.

3. Synthesis of a random copolymer of (a) methylmethacrylate and (b) a C₂ (preferably C₄)-or-higher alkyl (preferably isobornyl) methacrylate comprising anionic polymerisation of a mixmre of the respective monomers at a temperamre lower than - 40°C, preferably lower than -60°C.

4. Synthesis of a random or block copolymer according to claim 2 or 3, wherein some or all of the methylmethacrylate component (a) is replaced by a C₂ (preferably C₄)- or-higher alkyl methacrylate other than that chosen for component (b).

5. Synthesis according to any preceding claim, using a monofunctional alkali metal alkyl initiator, preferably monofunctional l ,l-diphenyl-3,3-dimethylbutyl lithium, for the anionic polymerisation.

6. Synthesis of an alky lmemaciy late-alky lene-alkylmethacrylate triblock copolymer, comprising (i) polymerisation of an alkylene monomer (preferably butadiene or isoprene) in a substantially apolar solvent (preferably cyclohexane and/or toluene), preferably with addition of a more polar solvent (preferably diethyl ether), to form a difunctional living polyalkylene block, followed by (ii) polymerisation, in the presence of that polyalkylene block, of an alkylmethacrylate by a method according to any of claims 1 to 4.

7. Synthesis according to claim 6, using a difunctional alkali metal alkyl initiator, preferably difunctional l,3-phenylene-bis(3,3-dimethylpentylidene)-dilithium, for the polymerisation of the alkylene monomer.

8. Synthesis according to claim 6 or 7, including the additional step of hydrogenating the polyalkylene block.

9. Synthesis according to any preceding claim, wherein anionic polymerisation of the isobornyl-or-other-alkyl-methacrylate is effected in the presence of a polar solvent, preferably comprising tetrahydrofuran and/or diethyl ether, preferably in a mixmre with substantially apolar solvent, preferably toluene and/or cyclohexane.

10. Anionically polymerised isobornylmethacrylate.

11. A diblock, multiblock, or random copolymer of methylmethacrylate and a C₂ (preferably C₄)-or-higher alkyl (preferably isobornyl) methacrylate, or of two or more C₂ (preferably C₄)-or-higher alkyl methacrylates with or without methymethacrylate.

12. An alkylmethacrylate-alkylene-alkylmethacrylate triblock copolymer wherein the alkyl groups of the alkylmethacrylate blocks comprise C₂ (preferably C₄)-or-higher (preferably isobornyl) alkyl groups.

13. A triblock copolymer according to claim 12, wherein the alkylene mid-blocks comprise polyisoprene, polybutadiene, poly(ethylene/butylene), or poly(ethylene/propylene), or mixmres thereof.

14. A triblock copolymer according to claim 12 or 13, wherein the alkylmethacrylate blocks comprise block or random copolymers of methylmethacrylate and a C₂ (preferably C₄)-or-higher alky (preferably isobornyl) methacrylate.

15. A copolymer according to any of claims 11 to 14, which is the product of anionic polymerisation using an alkali metal alkyl initiator, preferably in the presence of a polar solvent.

16. Synthesis according to any of claims 6 to 9, or a copolymer according to any of claims 12 to 15, wherein the said triblock copolymer incoφorates further blocks, preferably styrene blocks or alkyl methacrylate blocks, thus constimting a multi-block (preferably pentablock) copolymer.

17. A synthesis or copolymer according to claim 16, wherein the said multi-block copolymer comprises either (a) at least two different methacrylate blocks Ml , M2, or (b) at least one methacrylate block M and at least one styrene block S, on both ends of the alkylene mid-block A, the multi-block copolymer thus preferably having the pentablock structure (a) M1-M2-A-M2-M1 or M-S-A-S-M.

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