Core functionalised star block copolymers

Abstract: A core functionalised star block copolymer formed of i) at least one block of a vinyl aromatic hydrocarbon, and/or ii) at least one block of a conjugated diene and iii) a polyalkenyl aromatic coupling agent wherein the core functionalisation is provided by reaction of the star polymer core with an asymmetric bi- or polyfunctional capping agent.

Description: The present invention relates to core functionalised star block copolymers and processes for making them. More particularly, the invention relates to star block copolymers which have asymmetric bi- or polyfunctional capping agents extending from the cores of the block copolymer. Star block copolymers of conjugated dienes and/or vinyl aromatic hydrocarbons are well known and have been made commercially for many years. Such block copolymers are usually made by anionic polymerisation of the monomers to form living polymer arms which are then coupled with a polyfunctional coupling agent which usually is a polyalkenyl aromatic compound such as divinyl benzene. After the coupling of the arms to the core is completed, the core is still "living" and capable of further reaction. The living core is terminated by the addition of alcohols, water, acids, or other acidic (protic) species. For many reasons, it would be advantageous to introduce polar or low surface energy functionality into such star polymers. For example, polar functionality could increase the adhesion to polar surfaces of these polymers and lead to their wider use in adhesives or release agents. Such polymers might also be used in asphalt modification. U.S. 4,417,029 describes star block copolymers having functional groups associated with the nucleus of the copolymers. Most of the derivatizing agents described in this patent specification are monofunctional compounds. In every case, this monofunctional group is changed by the derivitization reaction itself, often to something less desirable. The few examples given of bifunctional derivatizing agents are symmetric, i.e., all of the functional groups are identical. In such a case, undesirable crosslinking tends to occur since the reaction is purely a statistical reaction. Crosslinking can be avoided by using a large excess of the derivatizing agent but this creates the disadvantage of having to remove a large amount of unreacted excess derivatizing agent. EP 0 540 109 describes a process for preparing asymmetric radial polymers. The coupling reaction is facilitated by means of a polar compound. EP 0 255 001 describes a bimodal star block copolymer and a process for its preparation wherein a polyfunctional coupling agent is used. US 4,244,862 describes compositions for paints and printing inks which comprise inorganic pigments and a block copolymer having a terminal polar group. GB 2144430 describes hydrogenated modified starshaped polymers having viscosity index-improving and dispersant properties and a process for their preparation. The process involves reacting the living star polymer with a carbonyl group containing organic compound, such as acetone or acetaldehyde. The present invention provides a method for avoiding these disadvantages. Since the capping agent contains the functionality which is desired to extend from the polymer core and also a functional group of high reactivity for the capping reaction and different from the desired functional group, high selectivity to the reaction which allows the desired functional group to extend from the core is obtained. This is obtained without altering the chemical structure of the desired functional group and without undesirable crosslinking reactions. Furthermore, the present invention allows the incorporation of functionality which was previously impossible to incorporate in anionic polymers, i.e. fluorine, NR 2 , (OCH 2 CH 2 ) x OR, and metallocene, since they are unreactive toward the lithiated core or are destroyed by it through metallation (lithiation). Accordingly, the present invention provides a core functionalised star block copolymer of i) at least one block of a vinyl aromatic hydrocarbon, and/or ii) at least one block of a conjugated diene and iii) a polyalkenyl aromatic coupling agent wherein the core functionalisation is obtainable by reaction of the star polymer core with a bi- or polyfunctional capping agent which is asymmetric, that is not all of the functional groups are identical, which capping agent incorporates a first type of functional group which is to extend from the core and a second type of functional group which reacts with the polymer core and attach the capping agent molecule to the core through the second functional group. The present star block copolymers have polar or low surface energy functionality extending from the core of the star block copolymer. In a preferred embodiment, the star block copolymer contains from 0.05 to 10 percent by weight of the first type of functional group. The polymers comprise at least one vinyl aromatic hydrocarbon and/or at least one conjugated diene. Such star block copolymers are made by reacting the living star block copolymer core with an asymmetric bi- or polyfunctional capping agent which incorporates the desired functionality (the first type of functional group) which is to extend from the core and the second type of functional group which will react with the living core and attach the molecule to the core through the latter functional group. Thus, according to a further aspect, the present invention relates to a process for making a core functionalised star block copolymer which comprises (a) preparing at least one set of polymer arms of at least one block of a vinyl aromatic hydrocarbon and/or at least one block of a conjugated diene by anionic polymerisation, (b) coupling the polymer arms with a polyalkenyl aromatic coupling agent and not terminating the coupling reaction, (c) capping the core of the living star polymer by reacting it with a bi- or polyfunctional capping agent which is asymmetric, that is not all of the functional groups are identical, which capping agent incorporates a first type of functional group which is to extend from the core and a second type of functional group which reacts with the polymer core to attach the capping agent molecule to the core through the second functional group, and (d) terminating the capping reaction and recovering the polymer. Suitably, from 0.05 to 10% by weight of the capping agent is used in step (c). Polymers containing ethylenic unsaturation can be prepared by copolymerising one or more polyolefins, particularly a diolefin. The copolymers may, of course, be random, tapered, block or a combination of these, as well as linear, star or radial. The polymers containing ethylenic unsaturation may be prepared using anionic initiators or polymerisation catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. In any case, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet, or a liquid. Polymers containing ethylenic unsaturation are available commercially from several suppliers. In general, when solution anionic techniques are used, copolymers of conjugated diolefins are prepared by contacting the monomer or monomers to be polymerised simultaneously or sequentially with an anionic polymerisation initiator such as group IA metals, their alkyls, biphenyls or anthracenyl derivatives. It is preferred to use an organo alkali metal (such as sodium, lithium or potassium) compound in a suitable solvent at a temperature within the range from -150°C to 300°c, preferably at a temperature within the range from 0°C to 100°C. Particularly effective anionic polymerisation initiators are organo lithium compounds having the general formula: Rli n wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to 20 carbon atoms and n is an integer of 1 to 4. Conjugated diolefins which may be polymerised anionically include those conjugated diolefins containing from 4 to 24 carbon atoms such as 1,3-butadiene, isoprene, piperylene, methylpenta-diene, phenyl-butadiene, 3,4-dimethyl-1,3-hexadiene, and 4,5-diethyl-1,3-octadiene. Isoprene and butadiene are the preferred conjugated diene monomers for use in the present invention. Vinyl aromatic hydrocarbons may also be included in the block copolymers. Styrene, alphamethyl styrene, and other substituted styrenes may be used, but styrene is the preferred vinyl aromatic hydrocarbon. The polymers of this invention may suitably comprise up to 50 percent by weight of the vinyl aromatic hydrocarbon. The star polymers of the present invention are block copolymers having at least three arms which comprise at least one block of a vinyl aromatic hydrocarbon and/or at least one block of a conjugated diene which are attached to a central core. Such polymers may suitably have up to 30 or 40 arms. As indicated above, the present star polymers are made by coupling polymer arms using a polyfunctional coupling agent or coupling monomer. A preferred coupling agent is a polyalkenyl aromatic coupling agent such as those described in U.S. 4,010,226, U.S. 4,391,949 and U.S. 4,444,953. U.S. 5,104,921 contains a complete description of such polyalkenyl aromatic compounds at columns 12 and 13. Divinyl aromatic hydrocarbons containing up to 26 carbon atoms per molecule are preferred and particularly divinyl benzene in either its meta, or para isomer and commercial divinyl benzene which is a mixture of said isomers is also quite satisfactory. The coupling agent is preferably added to the living polymer after the polymerisation is substantially complete. The amount of coupling agent varies between wide limits but preferably at least one equivalent is used per equivalent of unsaturated living polymer to be coupled. The coupling reaction is generally carried out in the same solvent as for the polymerisation reaction. The temperature applied in the coupling step (b) varies between wide limits, for example, in the range of from 25°C to 95°C. In general, any of the solvents known in the prior art to be useful in the preparation of such polymers may be used. Suitable solvents include straight- and branched chain hydrocarbons such as pentane, hexane, heptane, and octane, as well as, alkyl-substituted derivatives thereof; cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, and cycloheptane, as well as alkyl-substituted derivatives thereof; aromatic and alkyl-substituted derivatives thereof; aromatic and alkyl-substituted aromatic hydrocarbons such as benzene, napthalene, toluene, and xylene; hydrogenated aromatic hydrocarbons such as tetralin, and decalin; linear and cyclic ethers such as methyl ether, methylethyl ether, diethyl ether, and tetrahydrofuran. More specifically, the star polymers according to the present invention are made by the anionic polymerisation of the monomers in a hydrocarbon solvent at a temperature up to 100°C, preferably in the range of from 25 to 80°C, using an alkyl lithium initiator. The living polymer chains are usually coupled by addition of divinyl monomer to form a star polymer. Additional monomers may or may not be added to grow more branches or to terminally functionalise the polymer. It is important that the coupling goes as closely to completion as possible. Therefore, the coupling reaction will not be terminated. There must be at least one active site on the coupling agent core of the polymer. The asymmetric bi- or polyfunctional capping agent is then introduced to the polymer and reacted therewith. Generally, the conditions are 25 to 90°C for up to one hour and from 0.05 to 10% by weight of the agent is used. The exact method of reaction differs according to the nature of the capping agent. Suitable capping agents which may be used in accordance with the present invention are perfluoroaldehydes, perfluoroketones, perfluoroalkanoylchlorides, perfluoroesters, perfluoroetheresters, formylesters, polyoxyalkenylene esters, aminoaldehydes, metallocenealdehydes, epoxides of aldehydes, diepoxides of ketones, and epoxide derivatives of silanes. A metallocene is an organometallic coordination compound obtained as a cyclopentadienyl derivative of a transition metal. Two types of metallocenes useful herein are (1) dicyclopentadienyl-metals with the general formula (C 5 H 5 ) 2 M, and (2) monocyclopentadienyl-metal compounds with the general formula (C 5 H 5 MR 1_3 ), where R is CO, NO, or alkyl. The perfluoro capping agents add fluorine functionality to the core of the polymer. The formyl ester capping agents add ester functionality. The polyoxyalkenylene capping agents add polyoxyalkenylene, i.e. polyoxyethylene, and polyoxypropylene, functionality. The amino aldehydes add amino functionality. The metallocene aldehydes add metallocene functionality. Diepoxides add epoxide functionality. The preferred capping agents are those bearing perfluoro groups, polyether groups, amino groups, and epoxides. It is highly preferred that the asymmetric capping agents be chosen so that the reactivity of the first type of functional group which it is desired to have extend from the polymer core is much less than the reactivity of the second type of functional group which is to react with the polymer core to attach the molecule there. Obviously, this is important to increase the selectivity of the desired reaction as opposed to the opposite reaction. Table 1 below contains several examples of bi- or polyfunctional capping agents which leave the desired functionality completely unchanged and extend from the polymer core. After the capping agent reaction has proceeded, the reaction mixture is terminated with a proton source such as methanol, water, or acetic acid. The polymer is then separated from the polymer cement by conventional means. The star polymers capped with polyethers are useful in emulsions and water dispersions. Amines and epoxides are useful for adhesion to polar surfaces. Polymers capped with perfluoro groups are useful in applications requiring low surface energy, e.g., nonstick or release applications. EXAMPLES Example 1 The following is a description of the synthesis of a star polymer wherein 70 percent of the arms were styrene-isoprene diblocks (11,000 and 60,000, respectively, peak molecular weight as determined by gel permeation chromatography) and 30 percent of the arms were isoprene blocks (60,000 peak molecular weight as determined by gel permeation chromatography). These arms were coupled to a core of divinylbenzene which was not terminated so that the polymer which was available for reaction with the capping agents could be represented by the following formula: [(SI) 0.7 (I) 0.3 ] x (DVB) 3x Li x This master batch was synthesized to provide a living coupled star polymer for subsequent core functionalization reactions. The polymer had 15 to 30 arms. 326.6 kg cyclohexane and 4 kg of styrene were combined and 0.37 moles of sec-butyl lithium was added and the temperature increased to 50C and held there for 30 minutes to polymerise the styrene and produce living polystyryl lithium. Then 0.16 moles of sec-butyl lithium and 32.2 kg of isoprene were added to grow SI (styrene-isoprene) and I (isoprene) arms in parallel. The polymerisation was carried out at 60°C for 60 minutes. Then 1.59 moles of divinyl benzene (DVB) was added and the coupling reaction was allowed to proceed for one hour at 60°C. This gave a DVB:lithium molar ratio of 3:1. The coupling reaction was not terminated. The batch was split into aliquots for reaction with various functionalised capping agents. Example 2 54.5 litres of a cement containing the living star polymer was transferred to a pressure vessel. The cement contained 52 millimoles of living polymer. To this was added 10.2 grams of pentafluorobenzaldehyde (52 millimoles aldehyde:lithium ratio of 1:1). The vessel was rolled on a mechanical roller for 30 minutes at a temperature of 50°C and then the reaction was terminated with methanol. The cement was steam coagulated to give 3.63 kg of fluorinated core functionalised star polymer. The elemental analysis determined that the product contained 0.22 percent by weight of fluorine. This implies essentially complete capping of the DVB core with C 7 F 5 HO because the calculated amount of fluorine was 0.15 percent by weight. Example 3 Three liters (2400 grams) of the living cement of Example 1 was transferred to a 4.54 litre jug fitted with a septum. The cement contained 3.5 millimoles of living polymer. To this was added 2.1 grams of methyl perfluoro octanoate (5 millimoles). The jug was placed on a laboratory shaker and reacted for 30 minutes at 50°C and then terminated with methanol and coagulated with isopropyl alcohol. The product was collected by filtration and vacuum dried overnight at 50°C. 0.23 kg of fluorinated core functionalised star polymer was obtained. Elemental analysis showed 0.24 percent by weight of fluorine whereas the total possible calculated amount at a rate of 1 mole of the perfluoro compound per mole of lithium would be 0.4 percent by weight. Thus, the reaction proceeded to 60 percent completion. Example 4 This experiment was carried out according to the procedure of Example 3 except that the capping agent was perfluoroctanoyl chloride. The elemental analysis showed 0.39 percent by weight of fluorine whereas the total possible amount would be 0.4 percent by weight, indicating essentially complete reaction. Example 5 This experiment was carried out according to the procedure of Example 3 except that the capping agent was F-[CF(CF 3 )CF 2 O] 4 -CF(CF 2 )CO 2 CH 3 . The elemental analysis showed 0.22 percent by weight of fluorine whereas the calculated total possible amount was 0.8 percent by weight, indicating 27 percent conversion. Example 6 This experiment is carried out according to the procedure of Example 3 except that the capping agent is methyl-4-formyl benzoate and 6.4 millimoles of the capping agent is used. This reaction incorporates the functional group into the core of the star polymer wherein R is methyl. Example 7 This experiment is carried out according to the procedure of Example 3 except that the capping agent is R-(OCH 2 CH 2 ) 25 -OCH 2 CO 2 R and two millimoles of the capping agent is used. This reaction incorporates polyethylene oxide having a molecular weight of 1100 into the core of the star polymer. Example 8 This experiment is carried out according to the procedure of Example 3 except that the capping agent is 4-dimethylaminobenzaldehyde and 6.4 millimoles of the capping agent are used. This reaction incorporates the functional group into the core of the star polymer wherein R is methyl. Example 9 This experiment is carried out according to the procedure of Example 3 except that the capping agent is ferrocene carboxyaldehyde and 6.4 millimoles of the capping agent are used. This reaction incorporates -Fe(cyclopentadiene) 2 functionality into the core of the star polymer.

Claims: A core functionalised star block copolymer of i) at least one block of a vinyl aromatic hydrocarbon, and/or ii) at least one block of a conjugated diene and iii) a polyalkenyl aromatic coupling agent wherein the core functionalisation is obtainable by reaction of the star polymer core with a bi- or polyfunctional capping agent which is asymmetric, that is not all of the functional groups are identical, which capping agent incorporates a first type of functional group which is to extend from the core and a second type of functional group which reacts with the polymer core and attach the capping agent molecule to the core through the second functional group. The block copolymer according to claim 1, wherein the capping agent is selected from the group consisting of perfluoroaldehydes, perfluoroketones, perfluoroalkanoylchlorides, perfluoroesters, perfluoroetheresters, formylesters, polyoxyalkenylene esters, aminoaldehydes, metallocenealdehydes, epoxides of aldehydes, diepoxides of ketones, and epoxide derivatives of silanes. The block copolymer according to claim 1 or 2 which contains from 0.05 to 10 percent by weight of the first type of functional group. The block copolymer according to any one of claims 1 to 3, wherein the vinyl aromatic hydrocarbon is styrene. The block copolymer according to any one of claims 1 to 4, wherein the conjugated diene is isoprene or butadiene. The block copolymer according to any one of claims 1 to 5, which comprises up to 50 percent by weight of the vinyl aromatic hydrocarbon. A process for making a core functionalised star block copolymer which comprises (a) preparing at least one set of polymer arms of at least one block of a vinyl aromatic hydrocarbon and/or at least one block of a conjugated diene by anionic polymerisation, (b) coupling the polymer arms with a polyalkenyl aromatic coupling agent and not terminating the coupling reaction, (c) capping the core of the living star polymer by reacting it with a bi- or polyfunctional capping agent which is asymmetric, that is not all the functional groups are identical, which capping agent incorporates a first type of functional group which is to extend from the core and a second type of functional group which reacts with the polymer core to attach the capping agent molecule to the core through the second functional group, and (d) terminating the capping reaction and recovering the polymer. The process according to claim 7 wherein the capping agent is selected from the group consisting of perfluoroaldehydes, perfluoroketones, perfluoroalkanoylchlorides, perfluoroesters, perfluoroetheresters, formylesters, polyoxyalkenylene esters, aminoaldehydes, metallocenealdehydes, epoxides of aldehydes, diepoxides of ketones, and epoxide derivatives of silanes. The process according to claim 7 or 8 wherein from 0.05 to 10% by weight of the capping agent is used in step (c). The process according to any one of claims 7 to 9, wherein the temperature applied in step b) ranges from 25 to 95°C.

Inventors: HOXMEIER RONALD J, SOUTHWICK JEFFREY G, SPENCE BRIDGET A, HOXMEIER, RONALD J., SOUTHWICK, JEFFREY G., SPENCE, BRIDGET A.
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH
Application year: 1995
Main classification: C08F8
IPC codes: C08F297, C08F8