CA1257427A - Modified block copolymer process - Google Patents

Abstract

A B S T R A C T
MODIFIED BLOCK COPOLYMER PROCESS
Process for preparing a modified block copolymer comprising dissolving a block copolymer of the formula Bn(AB)oAp where n = 0 or 1, o = 0 or an integer of at least 1 and p = 0 or 1 and an acid moiety or its derivative in a suitable solvent, adding a free radical initiator, graft-reacting under free radical conditions, and recovering modified polymer product, wherein each A is predominantly a polymerized mono-alkenylaromatic hydrocarbon block having an average molecular weight of about 2,000 to 115,000; each B prior to hydrogenation is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight of about 20,000 to 450,000; the blocks A constitute 5-95 weight per cent of the copolymer; the unsaturation of the block B is less than 10% of the original unsaturation; and the unsaturation of the A blocks is above 50% of the original unsaturation. The process of the invention produces functionalized block copolymers which contain low residual unsaturation and high functionality. The modified block copolymers can be used for adhesives and sealants or compounded and extruded or moulded.

Description

~5~7~7 MO~IFIED BLOCK COPOLYMER PROCESS

This invention relates to a process for the production of novel selectively hydrogenated block copolymers functionalized with acid moieties or their derivatives. More particularly, it relates to a novel free radical initiated process for preparing in solution a block copolymer with enhanced properties by modifying a block copolymer composed of a con;ugated diene compound and an aromatic vinyl compound with an acid moiety or its derivative.
It is known that a block copolymer can be obtained by an aionic copolymerization of a con~ugated diene compound and an aromatic vinyl compound by using an organic alkali metal initiator. These types of block copolymers are diversified in characteristics, ranging from rubber-like characteristics to resin-like charactçristics, depending on the content of the aromatic vinyl compound.
When the content of the aromatic vinyl compound is small, the produced block copolymer is a so-called thermoplastic rubber. It is a very useful polymer which shows rubber elasticity in the unvulcanized state and is applicable for various uses such as mouldings of shoe sole etc.; impact modifier for polystyrene resins;
adhesive; binder; etc.
The block copolymers with a high aromatic vinyl compound 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 of packaging. Many proposals have been made on processes for the preparation of these types of block copolymers for example as described in U.S. Patent Specification 3,639,517. The elastomeric properties of certain aromatic vinyl polymers also appear to be due in part to their degree of branching.
While the aromatic vinyl polymers have a basic straight carbon chain backbone, those with elastomeric properties always have dependent ... ~

alkyl radicals. For example, EPR (ethylene-propylene rubber) has a structure of dependent methyl radicals which appears to provide elasticity and other elastomeric properties. When an essentially unbranched straight chain polymer is formed, such as some polyethy-lenes J the resulting polymer is essentially non-elastomeric or in other words relatively rigid, and behaves like a typical thermoplas-tic without possessing rubber-like resilience or high elongation, tensile strength without break, low set or other properties charac-teristic of desirable elastomers.
Block copolymers have been produced, see U.S. patent specifica-tion Re 27,145 which comprise primarily those having a general structure A--B--A
wherein the two terminal polymer blocks 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 having an optlmum combination of properties such that it behaves as a vulcanized rubber without requiring the actual step of vulcanization. Moreover, these block copolymers can be designed not only with this important advantage but also so as to be handled in thermoplastic forming equipment 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 princlpal limitations lies in their sensitivity to oxidation. This was due to their unsaturated character which can be minimized by hydrogenating the copolymer, especially in the centre section comprising the polymeric diene block. Hydrogenation may be effected selectively as disclosed in U.S. patent specification Re 27,145. These polymers are hydrogenated block copolymers having a configuration, prior to hydrogenation, of A-B-A wherein each of the A's is an alkenyl-substituted aromatic hydrocarbon polymer block and B is a butadiene polymer block wherein _ 3 _ ~5~7 35-55 mol per cent of the condensed butadiene units in the butadiene polymer block have 1,2-configuration.
These selectively hydrogenated ABA block copolymers are defic-ient in many applications in which adhesion is required due to its hydrocarbon nature. Examples include the toughening and compatibili-zation of polar polymers such as the engineering thermoplastics, the adhesion to high energy substrates of hydrogenated block copolymer elastomer based adhesives, sealants and coatings, and the use of hydrogenated elastomer in reinforced polymer systems. However, the placement onto the block copolymer of functional groups which can provide interactions not possible with hydrocarbon polymers solves the adhesion problem and extends the range of applicability of this material.
Functionalized S-EB-S polymer ("EB" refers to "ethylene-butylene") can be described as basically commercially produced S-B-S polymers which are produced by hydrogenation of S-B-S polymer to which is chemically attached to either the styrene or the ethylene-butylene block, chemically functional moiet`ies.
Many attempts have been made for the purpose of improving adhesiveness, green strength and other properties by modifying block copolymers with acid moieties and various methods have been proposed for modifying synthetic conjugated diene rubbers with acid moieties.
U.S. patent specification 4,292,414 describes a method for the production of monovinylaryl/conjugated diene block copolymer having low 1,2-content grafted with maleic acid compounds. U.S. Patent Specification 4,427,828 discloses a process for producing an acid functionalized high 1,2 content block copolymer. However, both processes involve "ENE" type reaction which rely on residual unsaturation in the block copolymer for the addition of functional groups. It is not possible to produce functionalized block polymers which contain low residual unsaturation along with reasonable functionalization using the "ENE" reaction. What was desired was a process to produce functionalized block copolymers which contain low residual unsaturation and high functionality.
According to the present invention, there is provided a process ~, 574 ~

for preparing a modified selectively hydrogenated high 1,2 content block copolymer by graft-reacting at least one acld moiety or lts derivative with the block copolymer.
More preferably there is provided a process for preparing a modified block copolymer by graft-reacting under free radical conditions an acid moiety or its derivative with a block copolymer selected from the group consisting of AB diblock copolymers and multiblock copolymers having at least two A end blocks and at least one B mid block wherein said graft reaction is carried out by dissolving said block copolymer and said acid moiety in a suitable solvent, adding a free radical initiator and recovering modified polymer product wherein each A is predominantly a polymerized monoalkenylaromatic hydrocarbon block having an average molecular weight of about 2,000 to 115,000; each B is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight of about 20,000 to 450,000; the blocks A constitute 5-95 weight per cent of the copolymer; the unsaturation of the block B is reduced to less than 10~ of the original unsaturation; and the unsaturation of the A blocks is above 50% of the original unsaturation.
Block copolymers of conjugated dienes and vinylaromatic hydrocarbons which may be utilized include any of those which exhibit elastomeric properties and those which have 1,2-micro-structure contents prior to hydrogenation of from about 7% to about 100%. Such block copolymers may be multiblock copolymers of varying structures containing various ratios of conjugated dienes to vinylaromatic hydrocarbons including those containing up to about 60 per cent by weight of vinylaromatic hydrocarbon. Thus, multiblock copolymers may be 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/vinylaromatic hydrocarbon tapered copolymer block and B is a polymer block of a conjugated diene. The block copolymer preferably has the general formula B (AB) A wherein n -- 0 or 1, o =

~S~ 7 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. Suitably, the blocks A comprise 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 addition of monomer techniques, incremental addition of monomer technique or coupling technique as illustrated in, for example, U.S. patene specifications ]0 3,251,905; 3,390,207; 3,598,887 and 4,219,627. As is well known in the block copolymer art, tapered copolymer blocks can be incorporated in the multiblock copolymer by copolymerizing a mixture of conjugated diene and vinylaromatic hydrocarbon monomers utilizing the difference in their copolymerization reactivity rates. The tapered copolymer blocks contain pre-dominantly one polymer, for example greater than 85%. Various patent specifications describe the preparation of multiblock copolymers containing tapered copolymer blocks including U.S.
patent specifications nos. 3,251,905; 3,265,765; 31639,521 and 4,208,356.

Conjugated 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), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like. Mixtures 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-methylstyrene, vinylnaphthalene, vinylanthracene and the like. The preferred vinylaromatic hydrocarbon is styrene.
According to a preferred embodiment of the present invention the block copolymer is a styrene-butadiene-styrene block copolymer.

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l~S7~7 The polymerized styrene blocks preferably have an average molecular weight between 4,000 and 60,000 and the polymerized butadiene blocks preferably have an average molecular weight between 35,000 and 150,000, suitably, in the range from 35 to 55 mol% and preferably 40 to 50 mol% of the condensed butadiene units in block B have a 1,2-configuration. Preferably, an average of less than 25% and more preferably less than 10% of the blocks A are hydrogenated. The average unsaturation 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, since many of these polymers and copolymers are commercially available, it is usually preferred to employ the commercially available polymer as this serves to reduce the number of processing steps involved in the overall process. The hydrogenation of these polymers and copo-lymers may be 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 hydrogenatlon 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 specifica-tions 3,113,986 and 4,226,952. The polymers and copolymers are hydrogenated in such a manner as to produce hydrogenated polymers and copolymers having a residual unsaturation content in the polydiene block of from about 0.5 to about 20 per cent, and preferably less than 5 per cent of their original unsaturation content prior to hydrogenation.
In general, any materials having the ability to react with the base polymer, in free radical initiated reactions are operable for ...~
,~ "

~5~7 ~ 7 --the purposes of the invention.
In order to incorporate functional groups into the base polymer, monomers capable of reacting with the base polymer in solution by free radical mechanism are necessary. Monomers may be polymerizable or non-polymerizable, however, preferred monomers are non-polymerizable or slowly polymerizing.
The monomers must be ethylenically unsaturated in order to take part in free radical reactions. We have found that by grafting unsaturated monomers which have a slow polymerization rate the resulting graft copolymers contain little or no homo-polymer of the unsaturated monomer and contain only short grafted monomer chains which do not separate into separate domains.
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 carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groupsj acid chlorides and the llke in addition to at least one point of unsaturation.
These functionalities can be subsequently reacted with other modifying materials to produce new functional groups. For example, a graft of an acid-containing monomer could be suitably modified by esterifying the resulting acid groups in the graft with appropriate reaction with hydroxy-containing compounds of varying carbon atoms lengths. The reaction could take place simultaneously 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 used for any purpose for which an unmodified material (base polymer) was formerly used. That is, they can be used for adhesives and sealants, or compounded and extruded and moulded in any convenient manner.
The preferred modifying monomers are unsaturated mono- and ~5~

polycarboxylic-containing acids (C3-C10) with preferably at least one olefinic unsaturation, and anhydrides, salts, esters, ethers, amides, nitriles, thiols, thioacids, glycidyl, cyano, hydroxy, glycol, and other substituted derivatives from 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 C1-C20 alkyl methacrylates, acrylic polyethers, acrylic anhydride, methacrylic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, acrylonitrile, methacrylonitrile, sodium acrylate, calcium acrylate and magnesium acrylate.
Other monomers which can be used either by themselves or in combination with one or more of the carboxylic acids or derivatives thereof include C2-C50 vinyl monomers such as acrylamide, acrylonitrile and monovinylaromatic compounds, i.e.
styrene, chlorostyrenes, bromostyrenes, a-methylstyrene, vinyl-pyridines and the like.
Other monomers which can be used are C4 to C50 vinyl esters, vinyl ethers and allyl esters, such as vinyl butyrate, vinyl laurate, vinyl stearate, vinyl adipate and the like, and monomers having two or more vinyl groups, such as divinyl-benzene, ethylene dimethacrylate, triallyl phosphite, dialkyl-cyanurate and triallyl cyanurate.
The preferred monomers to be grafted to the block copolymers according to the present invention are maleic anhydride, maleic acid, fumaric acid and their derivatives. It is well known in the art that these monomers do not polymerize easily. The acid moiety or its derivative may also be derived from a sulphonic acid or a derivative thereof.
Of course, mixtures of monomer can be also added so as to achieve graft copolymers in which the graft chains have at least two different monomers therein (in additlon to the base polymer monomers).

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The grafting reaction is initiated by a free-radical initiator which is preferably an organic peroxygen compound. Preferred peroxides include benzoyl peroxide,2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane, di-t-butyl peroxide, 2,5-dlmethyl-2,5-di-tert-butylperoxy-3-hexyne (known under the trade mark Lupersol 130), ~,~'-bis(tert-butylperoxy)diisopropylbenzene (known under the trade mark VulCup R), or any free radical initiator which is soluble in the reaction mixture and has a convenient half-liEe at the reaction temperature (see pages 66-67 of "Modern Plastics", November 1971, for a larger list of such compounds).
The concentration of the initiator used to prepare the modified polymer may vary between wide limits and is determined by the desired degree of functionality of the polymer and the reaction temperature. Typical concentrations based on polymer content range from about 0.001 weight per cent to about 5.0 weight per cent, more preferably between 0.01 and l.0 weight per cent.
The solvents which can be used in the process of the present invention are inert liquid solvents such as hydrocarbons, e.g., aliphatic hydrocarbons, such as pentane, hexane, heptane, octane,

2-ethylhexane, nonane, decane, cyclohexane, methylcyclohexane or aromatic hydrocarbons e.g., benzene, toluene, ethylbenzene, the xylenes, diethylbenzenes, propylbenzenes. Mixtures of hydrocarbons, e.g., lubricating oil may also be used.
The temperature at which the reaction is carried out may vary between wide limits such as from 0 C to 300 C, preferably from about 20 C to about 200 C. The reaction may be carried out in an inert atmosphere such as nitrogen and may be carried Ollt under pressure depending on the vapour pressure of the solvent used under reaction conditions.
Reaction 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 ,, - lo- ~7~
reaction temperature.
The process of the invention is highly flexible and a great many modifications such as those proposed above are available to achieve any particular purpose desired.
Of course, any of the standard additives can be used with these modified polymers. They include conventional heat stabilizers, slip~agents, antioxidants, antistatic agents, colorants, flame retardants, heat stabilizers, 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 substituted with functional groups such as chlorine, hydroxy, carboxy, nitrile, ester, amine and the like.
Furthermore, 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 1-7 The base polymer used in the following examples was Kraton G-1652 Rubber, a trade mark for a commercial S-EB-S block copolymer (average molecular weight 7500-37500-7500). This polymer was dissolved in 1200 grams of cyclohexane after which maleic anhydride was added and then Lupersol 101 or Lucidol 98 initiator.
"Lupersol 101" is a trade mark for 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane and "Lucidol 98" is a trade mark for benzoyl peroxide.
Benzoyl peroxide was used in all Examples except No. 5 which used Lupersol 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 2-propanol coagulation. Potentiometric titration analysis was used to determine the maleic anhydride content of the polymer. The results are presented in Table 1.

TABLE l Example Base Polymer, Maleic Anhydride, Initiator, Reaction % weight Maleic g g g Time _ Anhydride 1 120 1.2 6.0 17 h 0.44 2 120 3.6 6.0 1 h 11 min 1.25

3 120 3.6 3.0 2 h 15 min 1.22

4 120 1.2 6.0 2 h 0.77 120 1.2 30.5 ml of 1 h 27 min 0.42 75% sol~tion 6 120 7.23 6.0 42 min 0.36 7 120 14.42 6.0 23 min 0.25

Claims (25)

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

1. A process for preparing a modified block copolymer comprising dissolving a block copolymer of the formula Bn(AB)oAp where n = 0 or 1, o = 0 or an integer of at least 1 and p = 0 or 1 and an acid moiety or its derivative in a suitable solvent, adding a free radical initiator, graft-reacting under free radical conditions, and recovering modified polymer product wherein each A is predominantly a polymerized monoalkenylaromatic hydrocarbon block having an average molecular weight of about 2,000 to 115,000; each B prior to hydrogenation is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight of about 20,000 to 450,000; the blocks A constitute 5-95 weight per cent of the copolymer; the unsaturation of the block B is less than 10% of the original unsaturation and the unsaturation of the A blocks is above 50% of the original unsaturation.

2. The process of claim 1 wherein prior to hydrogenation, the polymeric blocks A are polymer blocks of styrene.

3. The process of claim 1 wherein the blocks A comprise 5-35 percent by weight of the copolymer, the unsaturation of block B is reduced to less than 5% of its original value and the average unsaturation of the hydrogenated block copolymer is reduced to less than 20% of its original value.

- 12a -

4. The process of claim 1 wherein the acid moiety or its derivative is derived from a maleic acid or its derivatives.

5. The process of claim 2 wherein A is a polymerized styrene block having an average molecular weight of between about 4,000 and 60,000.

6. The process of claim 5 wherein B is a polymerized butadiene block having an average molecular weight of between about 35,000 and 150,000, 35%-50% of the condensed butadiene units having 1,2 configuration.

7. The process of claim 6 wherein the unsaturation of block B has been reduced by hydrogenation to less than 15% of its original value.

8. The process according to claim 1 wherein an average of less than about 10% of the A blocks are hydrogenated.

9. The process according to claim 1 wherein an average of more than about 25% of the monoalkenylaromatic hydrocarbon units are hydrogenated.

10. The process of claim 1 wherein the acid moiety or its derivative is derived from carboxylic acid or its derivative.

11. The process of claim 1 wherein the acid moiety or its derivative is derived from a sulphonic acid or a derivative thereof.

12. The process of claim 1 wherein the acid moiety or its derivative is derived from a dicarboxylic acid or a derivative thereof.

13. The process of claim 1 wherein the solvent is an inert hydrocarbon liquid solvent.

14. The process of claim 1 wherein the solvent is selected from the group, consisting of pentane, hexane, heptane, octane, 2-ethylhexane, nonane, decane, cyclohexane, methylcyclohexane, benzene, toluene, ethylbenzene, xylene, diethylbenzene and propylbenzene.

15. The process of claim 1 wherein the reaction is carried out at between 0 °C and 300 °C.

16. The process of claim 1 wherein the reaction is carried out at between 20 °C and 200 °C.

17. The process of claim 1 wherein the initiator is an organo-peroxygen compound.

18. The process of claim 1 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-hexyne, .alpha.,.alpha.'bis(tert-butylperoxy)diisopropyl benzene, benzoyl peroxide.

19. A selectively hydrogenated functionalized block copolymer produced by the process of claim 1.

20. A selectively hydrogenated functionalized block copolymer produced by the process of claim 4.

21. The selectively hydrogenated functionalized block copolymer produced by the process of claim 6.

22. The selectively hydrogenated functionalized block copolymer produced by the process of claim 13.

23. The selectively hydrogenated functionalized block copolymer produced by the process of claim 1 containing from 0.02 to 20 weight per cent of the grafted portion.

24. The selectively hydrogenated functionalized block copolymer produced by the process of claim 1 containing from 0.1 to 10.0 weight per cent of the grafted portion.

25. The selectively hydrogenated functionalized block copolymer produced by the process of claim 1 containing from 0.2 to 5.0 weight per cent of the grafted portion.