WO2012156237A1

WO2012156237A1 - Use of multifunctonal initiator to prepare diblock copolymers comprising a monovinylaromatic polymer block.

Info

Publication number: WO2012156237A1
Application number: PCT/EP2012/058486
Authority: WO
Inventors: Valentin Poirier; Yann Sarazin; Jean-François Carpentier; Michel Duc
Original assignee: Total Research and Technology Feluy SA; Centre National de la Recherche Scientifique CNRS
Current assignee: TotalEnergies Onetech Belgium SA; Centre National de la Recherche Scientifique CNRS
Priority date: 2011-05-19
Filing date: 2012-05-09
Publication date: 2012-11-22
Anticipated expiration: 2013-11-19

Abstract

The present invention concerns a process to make a diblock copolymer having a monovinylaromatic polymer block and a block having ester or carbonate monomer units using both, ring opening polymerization (ROP) and radical polymerization.

Description

USE OF MULTIFUNCTONAL INITIATOR TO PREPARE DIBLOCK COPOLYMERS COMPRISING A MONOVINYLAROMATIC POLYMER

BLOCK.

Field of the invention.

The present invention concerns a process to make a diblock copolymer having a monovinylaromatic polymer block and a block having ester and/or carbonate monomer units such as by way of example lactic acid, glycolic acid, lactones, and/or trimethylene carbonate. The mixtures of the said diblocks with a monovinylaromatic polymer have a high transparency similar to the transparency of the monovinylaromatic polymer alone. These diblocks are useful as compatibilisers in mixtures comprising at least a polymer made essentially of the same monomer units as one of the blocks and at least a polymer made essentially of the same monomer units as the other block.

Common plastic material production draws on fossil (i.e. non-renewable) reserves, thus contributing to the depletion of essential and increasingly scare resources for mankind. Beyond recycling used plastic materials or valorising plastic wastes as fuel in incinerators for heat and electricity supply, it is desirable to incorporate some parts of polymers made from renewable resources in conventional plastics coming from petrochemistry. PLA (Poly(lactic acid)) is probably one of the so-called bio-polymers presenting the highest potential in terms of physical and mechanical properties, but also processability, considered as very close to polystyrene' ones.

Background of the invention.

Asawin Likhitsup et al. in J. Polym. Sci., Part A: Polym. Chem. 2008, 46(1 ), 102- 1 16 describe a one-step procedure developed for the preparation of bifunctional initiators capable of polymerising monomers suitable for atom-transfer radical polymerisation (ATRP) and ring-opening polymerisation (ROP). These bifunctional initiators were employed for making narrow disperse polystyrene macroinitiators, which were subsequently used for the ROP of various lactides to yield poly(styrene-block-lactide) copolymers. Thermogravimetric analysis (TGA) of these block copolymers shows a two-step degradation curve with the first step corresponding to the degradation of poly(lactide) segment and the second step associated with the poly(styrene) segment of the block copolymer. The bifunctional initiators were prepared by the esterification of 3-hydroxy-, 4- hydroxy-, and 3,5-dihydroxy-benzyl alcohols with a-bromoisobutyryl bromide and 2-bromobutyryl bromide. The esterified benzyl alcohols were employed in the polymerisation of styrene under copper (Cu)-catalysed ATRP conditions to yield macroinitiators with low polydispersity. These macroinitiators were subsequently used in the ROP of L-, D-, and racemic mixture of lactides. The formation of block copolymers was confirmed by gel permeation chromatography (GPC), spectroscopic and thermal characterisations. Abdiaziz A. Farah et al. in Polymer, 2006, 47, 4282-4291 have described Poly(£-caprolactone)-block-polystyrene metallopolymers via sequential ROP and ATRP conditions with in situ-generated ruthenium catalyst. They have prepared a macroligand (1) from ROP of (ε-caprolactone) with a hydroxy- functionalised bipyridine initiator catalysed by Sn(Oct)₂. The macroligand (1) with two distinct end functional groups per polymeric chain was converted to a tertiary bromoester macroinitiator (2) for the optimum performance of ATRP.

The functional macroinitiator (2) was then used in solution ATRP of styrene with the in situ-generated ruthenium catalyst [RuCl2(p-cymene)(PRs)] to generate a diblock type poly(£-caprolactone)-b-polystyrene (4) with vacant bipyridine binding sites at one polymer chain termination.

Chin-Feng Huang et al. in Polymer, 2005, 46 1561-1565 have described "A new strategy for the one-step synthesis of block copolymers through simultaneous free radical and ring-opening polymerisations using a dual- functional initiator". In this article is described a strategy for the one-step synthesis of block copolymers by using a combination of conventional free radical or reverse ATRP and ring-opening polymerisations. These strategies involve the use of a symmetric difunctional initiator that initiates simultaneous polymerisations of two comonomers by different polymerisation chemistries. In such an approach, the initiator remains attached to each type of growing chain. The two mechanisms of polymerisation must be compatible and tolerant of one another, as well as of the monomers, the reaction temperature must remain constant, and the kinetics must be nearly identical. Such a unimolecular dual initiator is able to combine two dissimilar polymerisation systems. The dual- functionalised initiator possesses a primary hydroxyl functionality, which is the initiation center for the living ROP of cyclic lactones or lactides, and an azo group, which initiates the radical polymerisation of vinyl monomers upon its thermal decomposition. A monomer mixture of styrene (S) and ε-caprolactone (CL) that is initiated by the dual initiator in the presence of Sn(oct)₂ as the ROP catalyst produces the diblock copolymer PS-b-PCL. The reaction route is illustrated as follows:

NHCHCH_jOH fCttSfz)

Eri Yoshida and Yusuke Osagawa have described in Macromolecules, 1998, 31 1446-1453 "Synthesis of Poly(£-caprolactone) with a Stable Nitroxyl Radical as an end-functional Group and Its application to a Counter Radical for Living Radical Polymerization". In said paper the quantitative synthesis of poly(£-caprolactone) (PCL) with 2,2,6,6-tetramethylpipehdine1 -oxyl (also known as TEMPO) at one chain end was attained through the anionic polymerisation of ε-CL by an aluminum tri(4-oxy-TEMPO), which was prepared by the reaction of triethylaluminum and 4-hydroxy-TEMPO. Said preparation is as follows:

Then ε-caprolactone was polymerised to produce poly(£-caprolactone) (PCL) with 2,2,6,6-tetramethylpiperidine-1 -oxyl at one chain-end, as shown hereunder:

The polymerisation of ε-CL was carried out in THF and not in styrene. Then said poly(£-caprolactone) with TEMPO at one end was placed in styrene in presence of benzoyl peroxide (BPO). Polymerisation is as follows:

The TEMPO-supported PCL behaved as a polymeric counter radical for the radical polymerisation of styrene, giving poly(CL-block-styrene) in quantitative efficiency. The radical polymerisation was found to proceed in accordance with a living mechanism, because the conversion of styrene linearly increased over time, and the molecular weight was directly proportional to the reciprocal of the initial concentration of the PCL. The resulting copolymers have two glass transition temperatures due to the PCL and polystyrene blocks and one melting endotherm based on the crystalline phases of PCL. Craig J. Hawker has described in Macromolecules, 1998, 31, 213-219, the making of diblock polymers of ε-caprolactone and styrene. Basic of the process involving functional ised alkoxyamine initiators is shown hereunder:

The dual, or double headed initiator, 1 , contains a single primary alcohol which is used as the initiating centre for the living ROP of lactones, as well as a secondary benzylic group which is an efficient initiator for the nitroxide-mediated "living" free radical polymerisation of vinyl monomers. The living ROP of ε-CL, 2, by 1 as the initiator was studied using a catalytic amount of aluminum tris(isopropoxide) as a promoter. Rifat Jabbar et al in J. Appl. Polym. Sci., 2008, 109, 3185-3195 have described "Nitroxide-Mediated Synthesis of Styrenic-Based Segmented and Tapered Block Copolymers Using Poly(lactide)-Functionalized TEMPO Macromediators". The following scheme describes a way to produce styrenic-based block copolymers with poly(lactide) (PLA) via ROP and subsequent nitroxide mediated polymerisation. a) ring opening polymerization of lac tide

poly(styrerie)-polf fladifle) Met* copolymer (PS-PLA)

First, the hydroxyl functional TEMPO (TEMPO-OH) is used, in combination with AIEt.3, as an initiator for the ROP of lactide to produce the poly(lactide) functionalised TEMPO mediator (PLAT) shown in (a). The PLAT mediator is then used to polymerise styrene or te/t-butyl styrene with a conventional initiator such as benzoyl peroxide (BPO) to make the desired styrenic-based block copolymer. The ROP of lactide is made in the presence of toluene as solvent, styrene is introduced only at step b). More, TEMPO-OH is used in a nearly stoechiometric amount versus the Al precursor to generate the polymerisation initiator.

The present inventors have recently discovered a more efficient process to make a diblock copolymer having a monovinylaromatic polymer block and a block having ester or carbonate monomer units. It is described in co-pending application WO/2010/012712. It discloses a process to make a composition comprising a block copolymer A-B that comprises the steps of:

a) forming a mixture comprising: one or more cyclic component polymerisable by ring-opening polymerisation (ROP) dispersed in at least one monovinylaromatic monomer,

optionally a rubber dissolved in the monovinylaromatic monomer,

b) contacting the mixture of step a) with a mixture of b1 and b2 such that : b1 ) is M[N(SiR⁸3)2]x in which M is a metal, R⁸ is an hydrocarbon group and x is the valency of the metal M,

or a metal alkoxide M(OR⁹)_x in which M is a metal, R⁹ is an hydrocarbon group and x is the valency of the metal M,

or a mixture thereof,

or a single-site metal catalyst component, for instance, based upon a bulky β-diiminate ligands (BDI), represented by the following general formula:

wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are each independently selected from hydrogen, unsubstituted or substituted hydrocarbyl, or inert functional group and wherein two or more of said groups can be linked together to form one or more rings, wherein X is an hydrocarbyl radical having from 1 to 12 carbon atoms, an alkoxide group OR^*, an amido group NR^** ₂ or a borohydride group (BH ).

or any other single site catalyst effective for ROP of cyclic esters or cyclic carbonates that have been described in detail for example in co-pending application WO2010/066597, or in another instance the Zn complexes based upon chelating phenoxy ligands, as described in EP 09 290318.6.

or any organic catalyst suitable for ROP of cyclic esters or cyclic carbonates

b2) a functional alcohol containing, besides its -OH function, another functionality Y enabling the growth or the grafting of a polyvinylaromatic, at conditions effective to produce by ROP of the cyclic component a block polymer A, having an -OH end and another function Y, dispersed in the monovinylaromatic monomer,

c) polymerising the solution obtained at step b) optionally in the presence of a free radical initiator, optionally in the presence of chain transfer agents, at conditions effective to produce:

a monovinylaromatic block polymer B linked to the block polymer A by the aforementioned functionality Y (or a functionality derived thereof) such that H-A-O-R-Y-B or H-A-O-R-B-Y (referred in both cases as A-B to simplify) in which R is a linking group,

d) optionally degassing the product of step c) to separate the optional unpolymerised monomers and comonomers and recovering optionally a composition comprising at least the block copolymer A-B. The present invention provides a further improvement on the previous methods.

Summary of the invention.

It is an objective of the present invention to prepare diblock copolymers having a monovinylaromatic polymer block and a block having ester and/or carbonate monomer units.

It is another objective of the present invention to use initiators commercially available on large scale to prepare diblock copolymers.

It is also an objective of the present invention to prepare diblock copolymers by a one-step process.

The foregoing objectives have been carried out as described in the independent claims. Preferred embodiments are described in the dependent claims.

List of figures. Figure 1 represents the gel permeation chromatography (GPC) traces of polymers for various monomer-to-alcohol ratios. Figure 2 represents the IR spectrum of the polylactide formed in the multi-step process of the present invention which is characterised by a combination of the IR spectra of classical PLLA and WAKO.

Figures 3a and 3b represent respectively the Size Exclusion Chromatography (SEC) of aliquots and final material resulting from experiments 1 and 2 in Table 2.

Figures 4a and 4b represent respectively the retention time curves of the polymers obtained with the one-step procedure and with the multi-step procedure.

Detailed description of the invention.

The present invention discloses a process for preparing a diblock copolymer having a monovinylaromatic polymer block and a block having ester and/or carbonate monomer units that comprises the steps of:

a) providing a compound of general formula

HO-R-Y-R'- OH herein R and R' are independently selected from hydrocarbyl groups containing from 1 to 20 C atoms or functional groups such as amido groups or ester groups as pendant functionalities or directly introduced in the hydrocarbyl chain or wherein R and R' are the same and are substituted aromatic groups selected for example from phenylene, tolylene, xylene, or naphthalene, and wherein Y is a group comprising a -N=N- (azo) function or Y is a group capable of generating free radicals selected for example from disulfide group -S-S- or from a group of formula - C(R^*)₂-(X)n-C(R^*)₂- wherein X is -N=N- (azo) or -O-O- (peroxy), wherein n is 0 or 1 and wherein R^* is selected from - CH₃, -Ph, or substituted phenyl, b) providing one or more cyclic monomer components polymerisable by ROP;

c) carrying out ROP of the monomer(s) of step b) in the presence of a suitable metallic or organic catalyst, in order to form P1-R-Y- R-P2;

d) heating to a temperature of at least 100 °C in order to break the R-N=N-R bonds to evolve N₂ from the Y group and concomitantly generate radical species of the type P1-R^" and P2-R" e) adding a monovinyl aromatic monomer;

f) carrying out the radical polymerisation of the monovinylaromatic monomer on each polymer chain P1-R^" and P2-R"; g) retrieving diblock copolymers P1-P3 and P2-P3.

In a preferred embodiment according to the present invention, the process is carried out in one-pot, one-step.

In such case, the compound of formula HO-R-Y-R'-OH, the one or more carbonate and/or ester monomers and the styrene are placed simultaneously in the reactor, and the mixture is heated to a temperature of at least 100 °C, resulting in the formation of P1-P3 and P2-P3 block copolymers.

In a first embodiment according to the present invention, R and R' are independently selected from hydrocarbyl groups containing from 1 to 20 C atoms, or functional groups selected from amido groups that can be selected from C(=0)NR^$2 wherein R^$ can be selected from Me, Et, Pr, iPr, Ph, or from ester groups selected for example from C(=0)OR^$. These functional groups can be introduced either as pendant functionalities or directly in the hydrocarbyl chain, and Y is a group comprising a -N=N- (azo) function. Preferably, R and R' are the same and are selected from tertiary alkyl groups or secondary benzylic groups, both possibly containing functionalities. More preferably the compound of step a) is

hereafter referred to as "Wako" or "VA-086".

That compound is stable up to a temperature of 80 °C and offers the advantage of being easily available.

In a second embodiment according to the present invention, R and R' are the same and are substituted aromatic groups selected for example from phenylene, tolylene, xylene, or naphthalene and wherein Y is a group capable of generating free radicals selected for example from disulfide group -S-S- or from a group of formula -C(R*)2-(X)_n-C(R*)2- wherein X is -N=N- (azo) or -O- O- (peroxy), wherein n is 0 or 1 and wherein R^* is selected from -CH₃, -Ph, or substituted phenyl. Suitable compounds of that type can be found in US-A- 5,079,310 and can be represented for example by formulae

An excess of the compound of formula HO-R-Y-R'-OH of step a) can be used with respect to the metallic/organic catalyst of c). The molar excess is in the range 1 to 200, preferably of 50 to 200. That compound acts as an activator of some metallic catalysts, eventually transforming in situ these catalyst precursors into an active metal-alkoxide species. For Lewis acidic catalysts or organic catalysts, Wako acts as an external initiator of the ROP process. When excess HO-R-Y-R'-OH is used, the alcohol functions act as transfer agent, thus generating as many polymer chains P1-R-Y-R -P2 as excess HO-R-Y- R'-OH molecules are introduced.

According to the operating conditions of step f) a portion of the monovinylaromatic monomer may also be polymerised as an homopolymer (or a copolymer when two or more monovinyl aromatic monomers are present) independantly of the diblocks P1-P3 and P2-P3. The mixtures of said diblocks with a monovinylaromatic polymer made by the above process are nanostructured. When there is essentially no rubber, they have a high transparency similar to the transparency of the monovinylaromatic polymer alone. In said mixtures, the monovinylaromatic polymer is made of the same monomer units as the P3 block.

When the above process produces the diblock P1-P3 and P2-P3 and essentially no monovinyl aromatic homopolymer independently of the diblocks, said diblocks recovered at step g) can be used as compatibilisers.

The diblocks P1-P3 and P2-P3 are useful as compatibilisers in mixtures comprising at least a polymer made essentially of the same monomer units as blocks P1 and P2 and at least a polymer made essentially of the same monomer units as the block P3. The present invention also relates to said mixtures. These mixtures are often nanostructured. The present invention also relates to a mixture comprising the diblock P1-P3 or P2-P3 and : - either one or more polymers made essentially of the same monomer units as the block P1 or P2,

- or one or more polymers made essentially of the same monomer units as block P3.

These mixtures are often nanostructured.

The cyclic component(s) polynnerisable by ROP can be selected from cyclic monomers or dimers of aliphatic hydroxycarboxylic acids. Examples of these include lactide, glycol ide, β-propiolactone, β-butyrolactone, γ-butyrolactone, γ- valerolactone, δ-valerolactone, ε-caprolactone and the like.

In the case of asymmetric carbon atoms within the hydroxy carboxylic acid unit, each of the D-form and the L-form as well as mixtures of both may be used. Racemic mixtures can also be used. By way of example the D-lactide is the cyclic dimer made of two D-lactic acid, the L-lactide is the cyclic dimer made of two L-lactic acid, the meso lactide is the dimer made of one D-lactic acid and one L-lactic acid. L, D-lactide or rac-lactide (rac-LA) designates a racemic mixture of L-lactide and D-lactide.

Other cyclic components polymerisable by ROP comprise cyclic carbonates and advantageously the 5- to 7-membered cyclic carbonates. Preferably, this polymerisation process is operative for 5- and 6-membered cyclic carbonates. As non-limitative examples, one can cite: trimethylenecarbonate (TMC), 2- benzyloxy-trimethylenecarbonate (BTMC), 2-hydroxy-trimethylenecarbonate (TMCOH), 4-(benzyloxymethyl)-1 ,3-dioxolan-2-one (BDMC), 4-(hydroxymethyl)- 1 ,3-dioxolan-2-one (DMCOH). In particular, one can cite cyclic carbonates such as 2-oxy-trimethylenecarbonate (OTMC), dehydrotrimethylenecarbonate (DHTMC) and 2,2 dimethoxy trimethylene carbonate (TMC(OMe)₂).

TMC TMCOH DHTMC BDMC

BTMC OTMC TMC(OMe)₂ DMCOH

ROP of trim ethylene carbonate is as follows:

The preferred monomer polymerisable by ROP is lactide (LA) and/or trimethylenecarbonate (TMC), more preferably L-LA.

The monovinylaromatic monomer can be selected from any aromatic bearing a vinyl function. By way of example, mention may be made of styrene, vinyl toluene, alphamethylstyrene, alphaethylstyrene, methyl-4-styrene, methyl-3- styrene, methoxy-4-styrene, hydroxymethyl-2-styrene, ethyl-4-styrene, ethoxy- 4-styrene, dimethyl-3,4-styrene, chloro-2-styrene, chloro-3-styrene, chloro-4- methyl-3-styrene, tert.-butyl-3-styrene, dichloro-2,4-styrene, dichloro-2,6- styrene,vinyl-1 -naphtalene and vinylanthracene. It would not depart from the scope of the invention to use more than one monovinylaromatic monomer. A part of the monovinylaromatic monomer may be replaced by unsaturated monomers copolymerisable with styrene. By way of example, mention may be made of alkyl esters of acrylic or methacrylc acid, acrylonitrile and methacrylonitrile. The proportion of comonomer may be from 0 to 50% by weight for respectively 100 to 50% of the monovinylaromatic monomer.

The preferred monovinylaromatic monomer is styrene.

The catalyst components that may be used in the ring-opening polymerisation of the cyclic monomer of step c) depend upon the nature of the monomer and are well known from the prior art and can be selected from metal complex or Lewis acidic metal salt or metal-free organic base.

Metallic complexes can be represented by formula MR"_n wherein M is a metal Group 2, 3 (including the lanthanide series, hereafter referred as Ln), 8, 12 or 13 of the periodic Table, wherein each R" is selected independently from hydrogen, an hydrocarbyl radical having from 1 to 12 carbon atoms, an alkoxide group OR^* wherein R^* is a linear or branched hydrocarbyl having from 1 to 12 carbon atoms, an amido group NR^** ₂ wherein R^** is of general formula YR^#3 wherein Y is Si or C and each R# is independently selected from hydrogen or hydrocarbyl having from 1 to 12 carbon atoms, a borohydride group or an halide, and wherein n is the valence of M.

Preferably, M is Mg(ll), Ca(ll), Y(lll), Fe(ll), Fe(lll), Zn(ll), or Al(lll).

Preferably each R is selected independently from an amido group such as N(SiMe₃)2, N(SiHMe₂)2, an alkoxide group OR' such as OiPr, OMe, OBn, or a borohydride group (BH₄)...

Alternatively, it can be selected from a single-site catalyst component based upon a bulky β-diiminate ligands (BDI) as described by Coates et al. (B.M. Chamberlain, M. Cheng, D.R. Moore, T.M. Ovitt, E.B. Lobkovsky, and G.W. Coates, in J. Am. Chem. Soc, 2001 , 123, 3229). It is represented by general formula

Wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are each independently selected from hydrogen, unsubstituted or substituted hydrocarbyl, or inert functional group andwherein two or more of said groups can be linked together to form one or more rings, wherein X is an hydrocarbyl radical having from 1 to 12 carbon atoms, an alkoxide group OR^* wherein R^* is a linear or branched hydrocarbyl having from 1 to 12 carbon atoms, an amido group NR^** ₂ wherein R^** is of general formula YR^#3 wherein Y is Si or C and each R# is independently selected from hydrogen or hydrocarbyl having from 1 to 12 carbon atoms, a borohydride group (BH₄).

Among the preferred metallic compounds according to the present invention, one can cite [BDI]Zn(N(SiMe₃)₂), {[BDI]Zn(OiPr),}₂, Zn(N(SiMe₃)₂), ZnEt₂, Y(N(SiMe₃)₂), Y(OiPr)₃, and AI(OiPr)₃ and Ln³OZn(N(TMS)₂), wherein TMS is trimethylsilyl.

One can also cite phenol-based pro-ligands as disclosed in EP-A-2253637, of formula

wherein ₍ 1

- R^a is (CH₂)_mNCH2CH2(OCH₂CH2)_n wherein m is 1 , 2 or 3 and n≥ 1 );

- R^b is hydrocarbyl group having 1 to 10 carbon atoms and is preferably selected from methyl, ethyl, iso-propyl, tert-butyl or neo-pentyl;

- R^c is the same as R^a or is hydrocarbyl group having 1 to 20 carbon atoms and is preferably alkyl selected from methyl, ethyl, iso-propyl, tert- butyl, neo-pentyl, cumyl, trityl or aryl selected from phenyl, 2,4,6- trimethylphenyl, 2,6-diisopropylphenyl. The key element in the substitution pattern is R^a which must simultaneously comprise a nitrogen function and an oxygen atom engaged in the cycle. It is a cycloazoether.

The metallic salt can be selected from metallic complexes of formula M'(OSO₂CF₃)n, hereafter referred to as triflates or OTf or M'(N(OSO₂CF₃)2)n, hereafter referred to as triflimidates or NTf₂ or M'(R^$C(O)CR₂C(O) R^$)_n, hereafter referred to as acetylacetonates or acac or (R"CO₂)_nM', hereafter referred to as carboxylates, wherein M' is a metal Group 2, 3, including the lanthanide series, hereafter referred as Ln, 4, 12, 13, 14 or 15 of the periodic Table, wherein each R^$ is selected independently from a linear or branched hydrocarbyl radical having from 1 to 12 carbon atoms, substituted or not by for instance an halogen or heteroatom, wherein each R" is selected independently from a perfluorinated alkyl or aryl residue having from 1 to 12 carbon atoms, and wherein n is the valence of M'.

Preferably, I is Mg(ll), Ca(ll), Sc(lll), Ln(lll) ,Y(III), Sm(lll), Yb(lll), Ti(IV), Zr(IV), Fe(ll), Fe(lll), Zn(ll), Al(lll) Sn(IV) or Bi(lll). More preferably, it is Al, Bi, Zn or Sc, Al and Zn being the most efficient metals, and most preferably Zn. Preferably each R^$ is selected independently from alkyl group such as CH₃ or a substituted alkyl group such as CF₃, More preferably, they are all the same and they are CR₃ or CF₃. Preferably, R" is (C6F₅) or (CF₃), or CF₃(CF₂)_m wherein m is an integer from 1 to 6. Among the preferred catalytic compounds according to the present invention, one can cite AI(OTf)₃, AI(NTf₂)₃, Mg(OTf)₂, Ca(OTf)₂, Zn(OTf)₂, Sc(OTf)₃, Bi(OTf)₃, Fe(acac)₃, AI(OCOCF₃)₃, Zn(OCOCF₃)₂, Zn(BF₄)₂, Zn(acac)₂.

These catalysts act by an activated monomer pathway, in the combination with an external nucleophile, typically the PC-(OH)_n compound.

The non-metallic organic compounds can be selected, as non limitative examples, from dimeric phosphazene bases as disclosed for example in Zhang et al. (Zhang L, Nederberg F., Messman J.M., Pratt R.C., Hedrick J.L., and Wade C.G., in J. Am. Chem. Soc, 2007, 129, 12610-1261 1 ) or phosphazene bases as disclosed for example in Zhang et al. (Zhang L, Nederberg F., Pratt R.C., Waymouth R.M., Hedrick J.L., and Wade C.G., in Macromolecules 2007, 40, 4154-4158) or organic compounds such as amines or guanidine as described for example in Nederberg et al. (Nederberg F., Lohmeijer G.B., Leibfarth F., Pratt R.C., Choi J., Dove A.P., Waymouth R.M., Heidrich J.L., in Biomacromolecules, 8, 153, 2007) or in Mindemark et al. (Mindemark J., Hilborn J., Bowden T., in Macromolecules, 40, 3515, 2007).

The amount of catalyst used for the ROP in step c) is advantageously selected to obtain a ratio of the cyclic component(s) polymerisable by ROP to catalyst ranging between 100 to 100 000, preferably of at least 1 000 and more preferably of at least 1 500.

The ratio of the number of equivalent of functional alcohol-to-catalyst ranges between 1 and 200. The polyester and/or polycarbonate blocks thus prepared show typically a unimodal molecular weight distribution that ranges from 1 .1 to 5.0, more typically from 1 .5 to 2.5. The number average molecular weight Mn can be tuned by the monomer-to- functional alcohol ratio and ranges from 1 000 to 1 000 000 g/mol, more typically from 10 000 to 250 000 g/mol.

In the first embodiment of the present invention comprising steps a) to g), the ROP of step c) can be carried out at moderate temperature. Advantageously said temperature is below 100 °C, preferably below 80 °C.

In the second embodiment according to the present invention, the one-step, one-pot method, the polymerisation is carried out at a temperature of at least 100 °C in order to break the R-N=N-R bonds in group Y.

A portion of the monovinylaromatic monomer may also be polymerised as a monovinylaromatic polymer independently of the above mechanism, following a usual radical mechanism. The proportion of the monovinylaromatic polymer is increasing with the presence of a chain transfer agent.

When the amount of monovinyl aromatic monomer is high enough and the temperature high enough, a substantial portion of the monovinyl aromatic monomer is also polymerised as an homopolymer (or a copolymer when two or more monovinyl aromatic monomers are present) independently of the diblocks P1 -P3 and P2-P3.

Examples

Materials. The catalyst used in the ROP of lactide was Ln³OZn(N(TMS)₂), wherein TMS is trimethylsilyl. e₃

It was prepared as described in EP-A-2253637.

Wako was obtained from Wako Chemicals Gmbh. Styrene (99+%) was received from Aldrich, dried over CaH₂ for a minimum of 48 hours, distilled by heating under dynamic vacuum and stored at 4 °C over activated molecular sieves; it was used within two weeks to avoid contamination by polystyrene. Toluene was pre-dried over sodium, and systematically distilled under Argon from a sodium mirror prior to use.

Typical rac-LA polymerisation procedure

All manipulations were performed under inert atmosphere. In the glove-box, the metallic initiator and the co-initiator WAKO were placed at once in a Schlenk tube, while the monomer rac-LA was loaded in a bent glass finger. The Schlenk tube and bent finger were sealed, and removed from the glove box. All subsequent operations were carried out on a Schlenk line, using standard Schlenk techniques. The required amount of solvent (toluene or styrene) was added with a syringe to the Schlenk tube containing the initiator and co-initiator, and the resulting mixture was stirred until complete dissolution of the solids was ensured. The monomer was added with the bent finger, and the polymerisation time was measured from this point. The reaction was terminated by addition of acidified MeOH (HCI, 1 wt-%) and the polymer was precipitated in hexane. It was purified by several re-precipitations, using THF as solvent and hexane as a non-solvent. The polymer was then dried to constant weight by heating at 60 °C under dynamic vacuum (<10^"2 mbar).

Polymer characterisation

Gel Permeation Chromatography (GPC) measurements were performed on a Polymer Laboratories PL-GPC 50 instrument equipped with a PLgel 5A MIXED- C column and a refractive index detector. The GPC column was eluted with THF at room temperature at 1 ml/min and was calibrated using 5 monodisperse polystyrene standards in the range 580-380 000 g.mol^"1. According to literature recommendations, [19] the molecular weights of all poly(lactide)s determined vs. polystyrene standards were corrected by a factor of 0.58.

Preparation of PLA-b-PS block copolymers Example 1 .

The preparation of PLA-b-PS block copolymers can be represented by scheme

In a first step, the ROP of lactide is carried out in the presence of metallic compound Ln³OZnN(TMS)₂.

The polymerisation conditions and results are displayed in Table I.

TABLE I.

Mn represents the number average molecular weight. PDI represents the polydispersity index defined as the ratio Mw/Mn of the weight average molecular weight over the number average molecular weight.

Figure 1 represents the gel permeation chromatography (GPC) traces of polymers for various monomer to alcohol ratios. It can be seen that the retention time increases when the ratio monomer/alcohol decreases, indicating that the molecular weight of the resulting polymer decreases.

Figure 2 represents the IR spectrum of the polylactide formed hereabove which is seen to be a combination of the IR spectra of classical PLLA and WAKO (VA- 086 stands for WAKO in this Figure).

Polystyrene was then grafted according to scheme

The grafting conditions and results are displayed in Table II.

TABLE II.

Figures 3a and 3b represent respectively:

- SECs of aliquots and final material resulting from experiment 1 , table 2

- SECs of aliquots and final material resulting from experiment 2, table 2

Example 2. The preparation of PLA-b-PS block copolymer was carried out in a one-step, one-pot process according to scheme

The block copolymer obtained had a number average molecular weight Mn of 56000 g/mol and a polydispersity index PDI of 2.56 as measured by GPC. The retention time curves were the same as those obtained with the multi-step procedure as can by comparing Figures 4a and 4b representing respectively the retention time curve of the polymer obtained with the one-step procedure and with the multi-step procedure.

Claims

CLAIMS.

1 . A process for preparing a diblock copolymer having a monovinylaromatic polymer block and a block having ester and/or carbonate monomer units that comprises the steps of:

a) providing a compound of general formula

HO-R-Y-R'- OH wherein R and R' are independently selected from hydrocarbyl groups containing from 1 to 20 C atoms or functional groups such as amido groups or ester groups as pendant functionalities or directly introduced in the hydrocarbyl chain or wherein R and R' are the same and are substituted aromatic groups selected for example from phenylene, tolylene, xylene, or naphthalene, and wherein Y is a group comprising a -N=N- (azo) function or Y is a group capable of generating free radicals selected for example from disulfide group -S-S- or from a group of formula - C(R^*)₂-(X)n-C(R^*)₂- wherein X is -N=N- (azo) or -O-O- (peroxy), wherein n is 0 or 1 and wherein R^* is selected from - CH₃, -Ph, or substituted phenyl, b) providing one or more cyclic monomer components polymerisable by ring-opening polymerisation ; and either

c) carrying out ring-opening polymerisation, in the presence of a suitable metallic or organic catalyst, of the monomer(s) of step b) in order to form P1 -R-Y-R -P2;

d) heating to a temperature of at least 100 °C in order to break the R-N=N-R' bonds and evolve N₂ from the Y group and concomitantly generate radical species of the type P1 -R^" and P2-R" e) adding a monovinyl aromatic monomer;

f) carrying out the radical polymerisation of the monovinylaromatic monomer on each polymer chain P1 -R^" and P2-R"; g) retrieving diblock copolymers P1 -P3 and P2-P3

or

c') placing the compound of step a), the monomer(s) of step b), a monovilyl aromatic monomer simultaneously in the reactor and heating to a temperature of at least 100 °C;

d') retrieving diblock copolymers P1 -P3 and P2-P3; wherein the ROP catalyst of step c) is selected from

A) a single-site catalyst component based upon a bulky β-diiminate ligands or metallic complex MR^* _n wherein, M is Mg(ll), Ca(ll), Y(lll), Fe(ll), Fe(lll), Zn(ll), or Al(lll), n is the valency of metal M, and each R is selected independently from hydrogen, an hydrocarbyl radical having from 1 to 12 carbon atoms, an alkoxide group, an amido group, a borohydride group or an halide;

B) a metallic salt selected from metallic complexes of formula M'(OSO₂CF3)n, M'(N(OSO₂CF3)2)n, or M'(R^$C(O)CR₂C(O) R^$)_n, or (R"'CO₂)_nM', wherein M' is a metal Group 2, 3, including the lanthanide series, hereafter referred as Ln, 4, 12, 13, 14 or 15 of the periodic Table, wherein each R^$ is selected independently from a linear or branched hydrocarbyl radical having from 1 to 12 carbon atoms, wherein each R'" is selected independently from a perfluorinated alkyl or aryl residue having from 1 to 12 carbon atoms, and wherein n is the valence of M';

C) non-metallic organic compounds selected from dimeric phosphazene bases.

2. The process of claim 1 wherein compound HO-R-Y-R'-OH of step a) is used in molar excess with respect to the metallic/organic catalyst of c) said molar excess ranging between 50 and 200.

3. The process of claim 1 or claim 2 wherein in the compound of step a) R and R' are the same and are selected from tertiary alkyl groups or secondary benzyl ic groups.

4. The process of any one of the preceding claims wherein the compound of step a) is

5. The process of any one of the preceding claims wherein the monomer component polymerisable by ring-opening polymerisation is selected from 5 to 7 membered cyclic carbonates or lactide, preferably L-lactide.

6. The process of any one of the preceding claims wherein the amount of catalyst used for the ROP is selected to obtain a ratio of the cyclic component(s) polymerisable by ROP/catalyst ranging between 100 to 100 000.

7. The process of any one of the preceding claims wherein the ratio of the number of equivalent of functional alcohol-to-catalyst ranges between 1 and 200.

8. The process of any one of the preceding claims wherein the heating of step d) is carried out at a temperature of at least 120 °C, preferably of at least 130 °C

9. The process of any one of the preceding claims wherein the monovinylaromatic monomer is selected from styrene. 10. The process of any one of the preceding claims wherein a portion of the monovinylaromatic monomer may also be polymerised as an homopolymer independantly of diblocks P1-P3 and P2-P3.

The process of claim 10 wherein the mixtures of homopolymers of monovinylaromatic monomers and diblocks P1 -P3 and P2-P3 are nanostructured.

12. Use according to any one of the preceding claims wherein diblocks P1 -P3 and P2-P3 are compatibilisers in mixtures comprising at least a polymer made essentially of the same monomer units as block P1 or block P2 or a polymer compatible with block P1 or block P2 and at least a polymer made essentially of the same monomer units as block P3 or a polymer compatible with block P3.