CA1233926A - Modified block copolymers and processes for the preparation therefor - Google Patents

Abstract

A B S T R A C T

MODIFIED BLOCK COPOLYMERS AND PROCESSES
FOR THE PREPARATION THEREFOR

Thermally stable, selectively hydrogenated monoalkenyl-aromatic hydrocarbon-conjugated diene block copolymers wherein at least one acid compound is grafted to the block copolymer at a secondary or tertiary carbon position and process for the preparation of such modified copolymers by a) melt-mixing a block copolymer and an acid moiety, adding a free radical initiator and graft-reacting under free radical conditions, or b) dissolving a block copolymer and an acid moiety in a suitable solvent, adding a free radical initiator and graft-reacting under free radical conditions.

Description

g Ye M~)DIFIED BI~CK COPOLYMERS OW) PP~OESS~S
FOR THE PFd~PARATION T~EFOR

This invention relates to novel selectively hydrogenated block copolymers and to two processes for preparing such copo-lymers.
It is kncwn that a block copolymer can be obtained by an S anionic copolymerization of a conjugated diene com~td and an aronEttic vinyl ccmpound by using an organic alkali metal initiator. These types of block copolymers are diversified in characteristics, ranging frcnt rubber-like characteristics to resin-like characteristics, depending on the content of the arcmatic vinyl compound.
When the content of the arcmatic vinyl cc~pound is small, the produced block copolymer is a so-call~d thern.oplastic rubber. It is a very useful polymer which shcws rubber elasticity in the unvulcanized state and is appliable for various uses such as mouldings of shoe sole, etc.; impact n~difier for polystyrene resins; adhesive; binder; etc.
The block copolymers with a high aromatic v myl cc~paund content, such as more than 70% by weight, provide a resin possessing both excellent impact resistance and transparency, and such a resin is widely used in the field ox packaging. Many proposals have been made on processes for the prepara-tion of these types of block copolymers, for example, as described in U.S. patent specification 3,6391517.
The elastcmeric properties of certain aromatic vinyl polymers also appear to be due in part to their deyree of branchiny. While the arGmatic vinyl polymers have a basic straight carbon chain backbone, those with elastcmeric So r Do I

prGperties always have dependent aIkyl radicals. For example, ERR (ethylene-propylene rubber) has a structure of dependent methyl radicals which appears to provide elasticity and other elastom,eric properties. When an essentially unbranched straight chain polymer is formed, such as SQme polyethylenes, the result-ing polymer is essentially non-elastameric or in other words relatively rigid, and behaves like a typical thermoplastic without possessing rubber-like resilience or high elongation, tensile strength without break, lcw set or other properties characteristic of desirable elastomers.
Block copolymers have been produced, see U.S. Patent Specification Re 27,145 which comprise primarily those having a general structure A~-B -A
wherein the two terminal polymer block A comprise thermoplastic polymer blocks of vinylarenes such as polystyrene, while block B
is a polymer block of a selectively hydrogenated conjugated - diene. The proportion of the thermoplastic terminal blocks to the centre elastomeric polymer block and the relative molecular weights of each of these blocks is balanced to obtaIn a rubber hazing an optimum ccmbination of prcperties such that it waves as a w,lcanized rubber without requiring the actual step of vulcanization. Moreover, these block ccpolymers can be desi~n~d, not only with this important advantage but also so as to be handled in thermoplastic forming equiFment and are soluble in a variety of relatively low cost solvents.
While these block copolymers have a number of outstanding technical advantages, one of their principal limitations lies in their sensitivity to oxidation. This was due to their em-saturated character which can be minimized by hydrogenating the copol~r, especially in the centre section ccmprising the polymeric diene block. Hydrogenation may be effected selectively as disclosed in U.S. patent specification Re 27,145. These polymers are hydrogenated block copoly~rs haviny a con-figuration, prior to hydrogenation, of A-B-A wherein each of the f A's i5 an alkenyl~substituted aranatic hydrocarbon polymer block and B is a butadiene polymer block wherein 35-55 mol per cent of the condensed butadiene units in the butadiene pol~ner bloc]c have l,2-configuration.
These selectively hydrogenated ABA block ccpolymers are deficient in many applications in which adhesion is required due to its hydrocarbon nature. Examples include the toughening and cornpatibilization of polar polymers such as the engineering thermoplastics, the adhesion to high energy substrates of hydrogenated block copolymer elastcmer based adhesives, sealants and coatings, and the use of hydrogenated elastcrner in re-inforced polymer systems. Hchever, the placernent onto the block ccpolymer of functional gralps which can provide interactions not possible with hydrocarbon polymers solves the adhesion problem and extends the range of applicability of this material.
Beyond the very dramatic improvement in interface adhesion in polymer blends, a functionalized S-EB-S co~,ponent can also contribute substan-tially to the external adhesion cnarac-teristics often needed in polymer systems. "EB" refers to "ethylene-but~lene". These include adhesion to fibres and fillers which reinforce the polymer system; adhesion Jo sub-strates in adhesives, sealants, and coatings based on functionalized S-EB-S polyrners, adhesion of decorations such as printing inks, paints, prirners, and metals of systems basecl on S-EB-S polymers; participation in chemical reactions such as binding pro-teins such as heparin for blood ccmpatibility;
surfactants in polar-non-polar aqueous or non-aqueous dispersions.
Functionalized S-EB-S polymer can be described as basically commercially produced S-EB S polymers which are prcduced by hydrog~lation of S-B-S polymer to which is cheTnically attached -to either the styrene or the ethylene-butylene blcck, chemically functional moieties.
Many attempts have been made for the purpose of improving adhesiveness, green strength and other properties by mcdifying block copolymers with acid ccn~cound having high functionality, and various methods have been proposed for modifyl~g synthetic conjugated diene rubbers with acid moieties.
U.S. patent specifications 4,292,414 and 4,308,353 describe a monovinylaryl/conjugated diene block copolymer with low 1,2-content grafted with a maleic acid ccmpound. However, the process is limited to reaction conditions wherein the generation of free radicals is substantially inhibited by using free radical inhibitors or conventional stabilizers, for example, phenol type, phosphorous type or amine type stabilizers. The processes are limited to thermal addition reactions or the so-called "ENE" reaction. This reaction scheme depends on unsaturation in the base polymer for reaction sites. A
reasonable amaunt of festal unsaturation must be present in order to obtain an advantageous degree of functionality or grafting onto the base polymer. A substantially completely hydrogenated base polymer would not react appreciably in this known process.
- U.S. patent specification 4,4-27,828 describes a similar modified block copolymer with high 1,2-content, however, again produced by the "ENE" reaction.
The IIEWEIl process as described in the prior art results in a modified polymer product which is substituted at a position on the polymer backkone which is allylic to the double bond. The reaction can be shcwn for maleic anhydride as follows:

a) to main chain unsaturation H H H H H H H
---C--C=C--C C--C--C=C Allylic position H H
A
C~C C=O o=c COO
\ / \/
o o b) to vinyl unsaturation H H
-C--C \ C--C--) Allylic position H C l H C

o=CF=~\CY~ o=c/--\c=o O . O

wherein a) represents addition across a double bond in the main chain of the base polymer and b) represents addition across a douhle bond occurring in a side chain. After addition and iso-merization the substitution is positioned on a carbon allyllc tothe double bond. -The allylically substituted polymers are prone to thermaldegradation due to their thermal instability. It is known in the art that allylic substituents can undergo what has been referr0d to as a contra-ENE reaction, see B.C. Tri~edi, B.M. CuLbertson, "Maleic Anhydride", (Plenum Press, New York, 1982~ pages 172 and 173.
Fur*her, because the ENE reaction requires a reasonable amount of unsaturation in the precursor base polymer, as discussed previously, the resulting functionalized copolymer product will have a significant amount of residual ~nsaturation and will be inherently unstable to oxidation.
Functionalized selectively hydrogenated thermoplastic block ccpolymers have ncw been found which are thermally stable, have a ]cw residual unsaturation, are excellent in appearance and transparency, have excellent melt-flow characteristics, have excellent mechanical properties such as tensile strensth and impact resistance and are particularly useful in blending with other polymers.

3 r } it Accordingly, the present invention provides a functionalized selectively hydrogenated block copoly~er cG~prising at least one block A and at least one block B, to which has been yrafted an acid ccmpound or a derivative thereof, wherein (1) each A is predominant.ly a polymerized monoalkenylaroma-tic hydrocarbon block having an average molecular weight in the range from 2,000 to 115,000;

(2) each prior to hydroyenation is predcmlnantly a LO polymerized conjuyated diene hydrocarbon block ha~iny an average molecular weight in the range from 20,000 to 450,000;

(3) the blocks A constitute 5-95 weight per cent of the copolymer;

(4) the unsa~uration of the block B is reduced to less than 10%
of the original unsaturation;

(5) thy unsaturation of the A blocks is above 50% of the origi,nal unsaburation; and

(6) substantially all of the acid co~pcunds or their derivatives are grafted to the block copolymer at secondary or tertiary carb~l positions in oh B blocks.
The modified block ccpolymers according to the present invention are substituted at a secondary or tertiary carkon position as shcwn in the exemplary reactions shown below:

c) H ' >' O=C / \ C-O Tertiary go A Position C O=C C=O C
\0/

~3~

d)--C--C--C--C O=C / \ SeoDndary H O=C C-O \ / Position \/ \~/.
O --I

The structure of the substituted block copolymer speci-fically determined by the location of the functionality on the polymer backbone at a secondary or tertiary position gives the block copolymer a substantially greater degre of thermal stability.
Block copolymers of conjugated dienes and vinylæamatic hydrocarbons which may be utilized include any of those which exhibit elastomeric prcperties and those which have 1,2-micro-structure contents prior to hydrogenation of ire abcut 7% to about 100~. Such block copolymers may be multiblock ccpolym~rs of varying structures containing various ratios of conjugated dienes to vinylarcmatic hydrocarbons including those containing up to about 60 p r cent by weight of vinylarcmatic hydrocarbon.
Thus, multiblock copolymers may ye utilized which are linear or radial, symmetric or asymmetric and which have structures represented by the formulae A-B, A-B-A, A-B-A-B, B-A, B-A-B, B-A-B-A, (AB)o 1 2 BA and the like wherein A is a polymer block of a vinyLaromatic hydrocarbon or a conjugated diene/-vinylarcmatic hydrocarbon tapered copolymer block and B is a polymer block of a conjugated diene. The block copolymer preferably has the general formula Bn(AB)oAp wherein n = O or 1, o - 0 or an integer of at least 1 and p = 0 or 1. Particularly preferred are block copolymers having at least one mid block B
and at least two end blocks A. Diblock copolymers AB are also very suitable. Suitably, the blocks A ccmprise 5 to 35 per cent and preferably 5 to 30 percent by weight of the block copolymer.
The block copolymers may be produced by any well-known block polymerization or copolymerization procedures including the well-known sequential additlon of monomer techniques, incremental addition of monomer technique or coupling technique as illustrated in, for example, U.S. patent sp cifications 3,251,905; 3,390,207; 3,5g8,887 and 4,219,627. As is well known in the block copolymer art, tapered copolymer blocks can be incorporated in the multiblock copolymer by copolymeriz mg a mixture of conjugated diene and vinylaromatic hydrocarbon moncmers utilizing the difference in their copolymerization reactivity rates. The tapered copolymer blocks contain pre-dcminantly one polymer, for example greater than 85%. ~ariouspatent specifications describe the preparation of multiblock cGpolymers containlng tapered copolymer blocks including U.S.
patent specifications 3,251,905; 3,265,765; 3,639,521 and ~,208,356.
C~niugated dienes which may be utilized to prepare the polymers and copolymers are those having from 4 to 8 carbon atoms per molecule and include - 1,3-butadiene, 2-methyl-1,3-butadiene(isoprene-3, 2,3-dimethyl-1,3-bu~adiene, 1,3-pentadiene, 1,3-hexadiene, and the like. Mixbures of such conjugated dienes may also be used The preferred conjugated diene is 1,3-butadiene.
Vinylaromatic hydrocarbons which may be utilized to prepare copolymers include styrene, o-methylstyrene, p-methylstyrene, p--tert-butylstyrene, 1,3-dimethylstyrene, alpha-m.ethylstyrene, vinylnaphthalene, vinylanthracene and the like. The preferred vinylaromatic hydrocarbon is styrene According to a pxeferred embodimEnt of the present invention the block copolymer is a styrene-butadiene-styrene block ccpolymer. The polymerized styrene blocks preferably have l averaye molecular weight between 4,000 and 60,000 and the poLymerized butadiene blocks preferably have an average molecular weight bet~7een 35,000 and 150,000. Suitably, in the range from 35 to 55 molt and preferably 40 Jo 50 mol% of the condensed butadiene units in block B have a 1,2-confi~uration.
Preferably, an average of less -than 25% and more preferably less than 10~ of the blocks A are hydrogenated. The average un~
saturation of the hydrogenated block copolymer has suitably been reduced to less than 20% of its original value.
It should be observed that the above-described polymers and copolymers may, if desired, be readily prepared by the methods set forth hereinbefore. However, s mce many of these polymers and copolymers are cc~mercially available, it is usually preerred to employ the commercially available polymer as this serves to reduce the number of processing steps involved in the L0 overall process. The hydrogenation of these polymers and copct lymers may ke carried out by a variety of well-established processes including hydrogenation in the presence of such catalysts as Raney Nickel, noble metals of Group 8 of the Periodic Table of the Elements, such as platinum and palladium, and soluble transition metal catalysts. Suitable hydrogenation processes which can be used are ones wherein the diene-con-taining polymer or copolymer is dissolved in an inert hydro~
carbon diluent such as cyclohexane and hydrogenated by reaction with hydrogen in the presence of a soluble hydrogenation catalyst. Such processes are disclosed in U.S. Patent Speci-fications 3,113,986 and 4,226,952. The polymers and copolymers are hydrogenated in such a nanner as to produce hydrogenated polymers and copoly~ers having a residual unsaturation con-tent in the polydiene b]ock of from abaut 0.5 to about 20 per cent, and preferably less than 5 per cent of their original I-saturation content prior to hydrogenation.
In general, any materials having the ability to react with the base polymer, in free radical initiated reactions are cperable for the purposes of the invention.
These polymers can be functionalized by free radical initiated reactions in the melt.
In order to incorporate functional groups into the base polymer, monomers capable of reacting with the base polymer, for example, in solution or in the melt by free radical mechanism are necessary. Monomers may be polymeri~able or non poly-merizable, however, preferred monomers are non-polymerizable or slowly poly~,erizing.
The ncmers must be ethylenically unsaturated in order to take part in free radi.cal reactions. We have found that by grafting unsaturated monomers which have a slow polymerization rate the resulting graft co~olymers contain little or no homo-polymer of the unsaturated ~.oncmer and contain only short grafted monGmer chains which do not separate into separate dGmains.
The class of preferred monomers which will form graft polymers in the process of the present invention have one or more functional groups or their derivatives such as car~oxylic acid groups and their salts, anhydrides, es-ters, imide groups, amide groups, acid chlorides and the like in addition to at least one point of unsaturation These functionalities can be subsequen-tly reacted with other modifying materials to produce new functional groups. For example, a graft of an acid-containing moncmer could be suitably mcdified by esterifying the resulting acid groups in the graft with appropriate reaction with hydro~y-containlng ccm~ounds of varying carbon atoms lengths. The reaction could take place simNltaneously with the grafting or in a subsequent post modification reaction.
The grafted polymer will usually contain from 0.02 to 20, preferably 0.1 to 10, and most preferably 0.2 to 5 weight per cent of grafted portion.
The block copolymers, as modified, can still be us for any purpose for which an unmLdified material (base polymer) was formerly used. That is, they can be used for adhesives and sealants, or ccmpounded and extruded and moulded in any con-venient manner.
The preferred mcdifying moncmers are unsaturated mono- and polyca~boxylic--containiny acids (C3-C10) with preferably at least one olefinic unsaturation, and anhydrides, salts, esters, ethers, amides, nitriles, -thiols, thioacids, glycidyl, cyano, f ~L1~3~ 3 hydroxy, gLycol, and other substituted derivatives frcm said acids.
Examples of such acids, anhydrides and derivatives thereof include maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, glycidyl acrylate, cyanoacrylates, hydroxy Cl-C20 alkyl methacrylates, acrylic polyethers, acrylic anhydride, methacrylic acid crotonic acid, ioscrotonic acid, mesaconic acid, angelic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, acrylonitrile, methacrylo-nitrile, sodium acrylate, calcium acrylate and magnesiumacryla-te.
Other monomers which can be used either by themselves or in combination with one or more of the carboxylic acids or derivatives whereof include C2-C50 vinyl monGmers such as acrylamide, acrylonitrile and monovinylarcmatic ccmpcunds, i.e.
styrene, chlorostyrenes, brc~,ostyrenes, ~-methylstyrene, vinyl-pyridines and the like.
ther mongers which can be used are C4-to C50 vinyl esters, vinyl ethers and allyl esters, such as vinyl butyrate, vinyl laura-te, vinyl ste æate, vinyl adipate and the like, and monaners having two or more vinyl groups, such as divinyl-benzene, ethylene dimethacrylate, triallyl phosphite, dialkyl-cyanurate and triallyl cyanurate.
The preferred moncmers to be grafted to the block copo-lymers according to the present inven-tion are maleic anhydride, maleic acid, funE~ic acid and their derivatives. It is well kncwn in the art that these monomers do not polymerize easily.
The acid cc~our.d may also be a sulphonic acid.
Of col~se, mLxtures of monomer can be also added so as to achieve grant copolymers in which the graft chains have at least two diEferent moncm2rs therein yin addition to the base pol~ner monomers) .
The invention further pr wides a process for preparing a novel functionkalized selectively hydrogenated block copoly~er as described hereinbefore, which process comprises melt-mixing a block copolymer comprising at least one block A and at least one block B, A and B having the same meaning as described hereinbefore, and an acid moiety or its derivative, adding a free radical initiator and graft-reacting under free radical conditions.
The modified polymer product may be recovered in any suitable nanner fram the reaction product thus cbtained.
Flcw prompters such as oils, law molecular weight resins or other polymers can be included in the reaction mixture during the functionalization step.
Reaction temperatures and pressures should be sufficient to melt the reactants and also sufficient to thermally deccmpose the free radical initiator to form the free radical. Reaction temperatures wauld depend on the base polymer being used and the free radical initiator being used. Typical reaction conditions can be obtained by using a screw type extruder to mux and melt the reactants and to heat the reactant mixture to the desired reaction temperature. Useful te~,peratures may vary between wide limits, such as fram +75 C to 450 C, preferably fram 200 C to 300 C.
The invention also provides a process for prepar mg a functionali ed selectively hydrogenated block copolymer as described hereinbefore, which process camprises dissolving a block copolymer ccmprising at least one block A and at least one block B, A and B having the same meaning as described hereinbe~ore, and an acid moiety or its derivative in a suitable solvent, adding a free radical initiator and graft-reacting under free radical conditions. The modified polymer product ma be recovered in any suitable manner fram the reaction product thus obtained.
The solvents which can be used in the latter process are inert liquid solvents such as hydrocarbons, e.g., aliphatic ydrocarbons, such as pentane, hexane, heptane, octane, 2-ethyl-hexane, nonane, decane, cyclohexane, methylcyclohexane or aramatic hydrocarbons, e.g., benzene, toluene, ethylbenzene, the xylenes, diethylbenzenes, propylbenzenes. Mixtures of hydro-carbons, eOg., lubricating oil may also be used.
me temperature at which the latter process according to the present invention is carried out may vary between wide limits such as from 0 C to 300 C, preferably from 20 C to 200 C. me reaction may be carried out in an inert atmosphere such as ni-trogen and may be carried out under pressure depending on the vapour pressure of the solvent used under reaction conditions. Reactlon temperatures and pressures should be sufficient to thermally decompose the free radical initiator to form the free radical. Reaction temperatures would depend on the base polymer being used and the free radical initiator being used. Typical reaction conditions can be obtained by using, for example, an autoclave type reactor to heat the reactant mixture to the desired reaction temperature.
m e grafting reaction is initiated by a free radical initiator which is preferably an organic peroxygen cc~pound.
Especially preferred peroxides are 2,5-dimethyl-2,5-di~t-butyl-pe m ~y)hexane, di-t-butyl perc~ide, 2,5-dimethyl~2,5-di-tert-butylperoxy-3-hexyne known under the trade mark Lupersol 130), ~,~'-bis(tert-butylperc~y)diisopropyIbenzene known under the trade mark VulCup R), or any free radical initiator hav mg a short half-life under the base polymer processing conditions.
See pages 66-67 of "Modern Plastics", November 1971, for a larger list of such ccmpounds.
The concentration of the initiator used to prepare the mock fied polymer may vary between wide limits and ls determined by the desired degree of functionality and degradation allowable. Typical concentrations range frcm about 0.001 weight per cent to about 5.0 weight per cent, more preferably between 0.01 and 1.0 weight per cent.
The process of the invention is highly flexible and a great many modifications such as those proposed above cure available to achieve any F~rticular purpose clesired.
Of course, any of the standard additives can be used with 3~rJ r1~d ~Jl these modified polymers. They include conventional heat stabilizers, slip-agents, antioxidants, antistatic agents colorants, flame retardants, heat stabillzers, plasticizers, preservatives, processing aids and the like.
It is to be emphasized that in the definition of the base polymer, substituted polymers are also included; thus, the backbone of the polymer before functionalization can be sub-stituted with functional groups such as chlorine, hydroKy, cæboxy, nitrile, ester, amine and the like.
Fur;hermore, polymers which have been functionalized, particularly those with functional carboxylic acid groups, can be additionally cross-linked in a conventional manner or by using metallic salts to obtain ionomeric cross-linking.
The present invention will be further illustrated by the following examples.
Examples 1-4 and Comparative Experiment A
me base polymer used in the following examples was Kraton G~1652 Rubber, a trade mark for a ccmmercial S-EB-S block c~polymer (average molecular weight 7500-37500-7500). This polymer was melt reacted with maleic anhydride and Lupersol 101 in a 30 mm diameter corotating twin screw extruder. "Lupersol 101" is a trade mark for 2,5-dimethyl-2,5-di(t-bu~ylperoxy)-hexane.
The reactants were prenuxed by tumbling in polyethylene bags and then fed into the extruder. For the experiments, all extrusion conditions except for reactant concentrations were kept constant. The follcwing two-stage screw configuration was used: the first stage comprised a 6 mm spacer, a 75 mm feed section, eight mixing cams, and an orifice ring pair. The second stage was identical except for a feed section 45 mm long. The melt temperature was kept at 150 C in the feed zone and increased to 260 C by the time material reached the die. The extruder was starve fed with the first orifice ring pair left open. In the second stage, flow was restricted with the second orifice ring pair. A screw speed of 350 rpm was used, leading to ?

an output of 4.5 kg per hcur.
The samples prepared in the manner described hereinbefore were first analysed for base polymer degradation my measuring gel content as determined hy hot tetrahydrofuran (THF) insolubles. This was accomplished by extraction with refluxing tetrahydrofuran. The soluble fraction of the sample was then recovered by precipitation of the extractant into isopropyl alcohol. I'his precipitation separated the unbound maleic anhydride from the base polymer. The precipitated polymer was then dried at s~-atmospheric pressure to convert all functional groups to the anhydride form, as verified by infrared measure-ments. The maleic anhydride graft content of the soluble fraction of the samples was then measured by titration with potassium methoxide.
Table 1 shows the various reactant concentrations examined, as well as analytical results for the materials prepared.

tn a 0 03 N N O

O

_~
~!
.
;~

l 'I N or ~3~

In Ccmparative ExperIment A maleic anhydride could not be grafted to the base polymer within the li its of detection of the analytical technique used without addition of a free-radical initiator. In Examples 1-3 a wide range of functionality levels s were obtained by the free radical initiated melt grafting technique. In EXample 4 severe base polymer degradation has -taken place when too high a level of free radical initiator is used.
Example 5 EXtruder grafting conditions used were the same as for the ahove examples.
100 parts of a 70/30 weight per cent mixture of anionically polymerized ethylene-butylene copolymer (140,000 molecular weight) and anionically polymerized homDpolystyrene (50,000 molecular weight) were tumbled (dry blended) with 3 parts of maleic anhydride and 0.1 parts of Lupersol 101. This mixture was extruded under the previous grafting conditions.
A 10 gram sample of the extruded ccmposition was dissolved in 200 ml chloroform and the solution was then added to 1200 ml of acetone to precipitate the E6 copolymer ccmponent which was then recovered by filtrations and washing in acetone.
A sample of this EB copolymer component was then analysed by infrared spectroscopy. The IR spectrum shcwed characteristic acid anhydride bands at between abcut 1700 cm and 1800 on showing the presence of maleic anhydride bound to the EB ccpo-lymer ccmponent.
The polystyrene-chloroform-acetone mixt~lre Fran the previous step was held at sub-atmospheric pressure at 90 C in a Roto Vap for 30 minutes to remove unbound (free) maleic anhydride and to concentrate the solution in preparation for casting an IR filrn sample. The sample was analysed and showed essentially no presence of maleic anhydride. This result showed that there was no maleic anhydride bound to the styrene component.
Fr~n-the above experiments it can be concluded that the maleic anhydride is rated to -the EB lmid-block) ccmponent in the block copolymer.

it EXample 6 Iwo S-EB-S block copolymers similar to Kraton G-1652 were prepared having residual unsaturations of 0.170 and 0.098 milliequivalents of double bonds per gram. These copol~mers were extruder grafted using the same extruder conditions as in the s previous examples. Again 3.0 weight per cent maleic anhydride and 0.1 weight per cent of Lupersol 101 were used. Both extruded materials were analysed as above for bound maleic anhydride by titration with potassium methoxide.
It was found that both samples contained 1.6 weight per cent of maleic anhydride. Therefore, it can be concluded that the degree of residual unsaturation does not affect the graft reaction.
Example 5 shows that graft mg had occurred in the EB block.
I'he EB block contains five possible classes of carbon atoms where grafting can occur: 1, 2, 3, allylic and vinyl carbons.
Allylic and vinyl carbons are associated with unsaturation.
Example 6 showed that the level of residual unsaturation does not affect the graft reaction. Therefore, it can be concluded that grafting is not occurring at these carbons.
It is well kncwn that the reactivity of the 1, 2, 3 carbons is related to the ease of formation of free radicals resulting Fran hydrogen abstraction and follows the relationship 3>2>1. 1 carbons are not kinetically favoured and occur infrequently. Since the 3 carbon is most favoured kinetically to react and since the 2 carbons occur more frequently, substantially all of the grafting should occur at the 2 and 3 carbons .
Examples 7-13 The base polymer used in the following examples was Kraton G-1652 Rubber, a trade mark for a commercial S-EB-S block copolymer (coverage molecular weight 7500-37500-7500). This polymer was dissolved in 1200 grams of cyclohexane after which maleic anh~dride was added and then Lupersol 101 or Lucidol 98 initiator. "Lupersol 101" is a trade mark for 2,5-dimethyl-J

2,5-di(t-butylperoxy)hexane and "Lucidol 98" is a trade maxk for benzoyl peroxide. Eenzoyl peroxide was used in all Examples except EXample 11 which used I.upersol 101.
The reactants were added to a glass reactor which was then heated -to the boiling point of the solvent (cyclohexane) and the contents refluxed. Upon completion of the reaction, when peroxide was consumed, the reactor was cooled and the polymer precipitated by coagulation with isopropyl alcohol.
Potentio~etric titration analysis was used to determlne -the maleic anhydride con-tent of the polymer. The results are presented :Ln Table 2.

it C) o o o o o .~

~o,o`o o o o .~ I` or .~

o o o o o o o N

o, ,,

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A functionalized selectively hydrogenated block copolymer comprising at least one block A and at least one block B, to which has been grafted an acid compound or its derivative, wherein:
1) each A is predominantly a polymerized monoalkenylaromatic hydrocarbon block having an average molecular weight in the range from 2,000 to 115,000;
2) each B prior to hydrogenation is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight in the range from 20,000 to 450,000;
3) the blocks A constitute 5-95 weight per cent of the copolymer;
4) the unsaturation of the block B is reduced to less than 10% of the original unsaturation;
5) the unsaturation of the A blocks is above 50% of the original unsaturation; and 6) substantially all of the acid compounds or their deriva-tives are grafted to the block copolymer at secondary or tertiary carbon positions in the B blocks.

2. A functinalized selectively hydrogenated block copolymer as claimed in claim 1, which has the general formula Bn(AB)oAp wherein n = 0 or 1, o = 0 or an integer of at least 1 and p =0 or 1.

3. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, which has at least one mid block B and at least two end blocks A.

4. A functionalized selectively hydrogenated block copolymer as claimed in claim 1 wherein the blocks A comprise 5 to 35 per cent by weight of the block copolymer.

5. A functionalized selectively hydrogenated block copolymer as claimed in claim 1 wherein an average of less than 10% of the blocks A have been hydrogenated.

6. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the unsaturation of block B has been reduced to less than 5% of its original value.

7. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the average unsaturation of the hydrogenated block copolymer has been reduced to less than 20% of its original value.

8. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the block copolymer is a styrene-butadiene-styrene block copolymer.

9. A functionalized selectively hydrogenated block copolymer as claimed in claim 8, wherein the polymerized styrene blocks have an average molecular weight between 4,000 and 60,000.

10. Functionalized selectively hydrogenated block copolymer as claimed in claim 8, wherein the polymerized butadiene blocks have an average molecular weight between 35,000 and 150,000.

11. A functionalized selectively hydrogenated block copolymer as claimed in any one of claims 8, 9 or 10, wherein in the range of from 35% to 55% of the condensed butadiene units have 1,2-configuration.

12. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the acid compound is an unsaturated carboxylic acid.

13. A functionalized selectively hydrogenated block copolymer as claimed in claim 12, wherein the acid compound is maleic acid, or a derivative thereof.

14. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the acid compound is a sulphonic acid.

15. A functionalized selectively hydrogenated block copolymer as claimed in claim 1, wherein the grafted acid compound or a derivative thereof is present in an amount between 0.02 and 20 per cent by weight.

16. A functionalized selectively hydrogenated block copo-lymer as claimed in claim 15, wherein the grafted acid compound or a derivative thereof is present in an amount between 0.1 and 10 per cent by weight.

17. A functionalized selectively hydrogenated block copo-lymer as claimed in claim 16, wherein the grafted acid compound or a derivative thereof is present in an amount between 0.2 and 5 per cent by weight.

18. A process for preparing a functionalized selectively hydrogenated block copolymer as claimed in claim 1, which process comprises melt-mixing a block copolymer comprising at least one block A and at least one block B, A and B having the same meaning as in claim 1, and an acid moiety or its derivative, adding a free radical initiator and graft-reaeting under free radical conditions.

19. A process as claimed in claim 18, wherein a flow pro-moter is added.

20. A process as claimed in claim 19, wherein the flow pro-moter is an oil.

21. A process as claimed in claim 19, wherein the flow pro-moter is a low molecular weight resin.

22. A process for preparing a functionalized selectively hydrogenated block copolymer as claimed in claim 1, which process comprises dissolving a block copolymer comprising at least one block A and at least one block B, A and B having the same meaning as in claim 1, and an acid moiety or a derivative thereof in a suitable solvent, adding a free radical initiator and graft-reacting under free radical conditions.

23. A process as claimed in claim 22, wherein the solvent is an inert hydrocarbon liquid solvent.

24. A process as claimed in claim 23, wherein the solvent is selected from the group consisting of petane, hexane, heptane, octane, 2-ethylhexane, nonane, decane, cyclohexane, methylcyclo-hexane, benzene, toluene, ethylbenzene, xylene, diethylbenzene and propylbenzene.

25. A process as claimed in claim 22, wherein the reaction is carried out at a temperature between 0°C and 300°C.

26. process as claimed in claim 25, wherein the reaction is carried out at a temperature between 20°C and 200°C.

27. A process as claimed in claim 18, wherein the acid moiety or a derivative thereof is derived from a carboxylic acid or a derivative thereof.

28. A process as claimed in claim 27, wherein the acid moiety or a derivative thereof is derived from a dicarboxylic acid or a derivative thereof.

29. A process as claimed in claim 18, wherein the acid moiety or a derivative thereof is derived from a sulphonic acid or a derivative thereof.

30. A process as claimed in claim 18, wherein the initiator is an organo peroxygen compound.

31. A process as claimed in claim 30, wherein the initiator is selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy-3-hexane, .alpha.,.alpha.'-bis(tert-butylperoxy)diisopropyl-benzene.

32. A process as claimed in claim 22, wherein the acid moiety or a derivative thereof is derived from a carboxylic acid or a derivative thereof.

33. A process as claimed in claim 32, wherein the acid moiety or a derivative thereof is derived from a dicarboxylic acid or a derivative thereof.

34. A process as claimed in claim 22, wherein the acid moiety or a derivative thereof is derived from a sulphonic acid or a derivative thereof.

35. A process as claimed in claim 22, wherein the initiator is an organo peroxygen compound.

36. A process as claimed in claim 35, wherein the initiator is selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy-3-hexane, .alpha.,.alpha.'-bis(tert-butylperoxy)diisopropyl-benzene.