Patent EA-001222-B1 (EA)
Title: A process for producing a polymer having a bimodal molecular weight distribution, a process for modifying the molecular weight distribution of a random copolymer of isobutylene, a polymer product and a polymer composition based thereon
Inventor: WHIT DONALD ANDREW
IPC: C08F255/00
Filed: 1996-05-23
Abstract: 1. A process for producing a polymer having a bimodal molecular weight distribution from a polymer having a monomodal molecular weight distribution, molecular weight of which decreases when it is subjected to high shear mixing optionally in the presence of free radical polymerization initiator, characterised in that starting polymer is selected from the group, consisting of polypropylene, copolymers of propylene with up to 10 wt % ethylene, polyisobutylene, copolymers of a C4-C7 isomonoolefin with up to 10 wt % isoprene and copolymers of a C4-C7 isomonoolefin with up to 20 wt % of para-alkylstyrene;  the mixture of such polymer with polyunsaturated crosslinking agent and, optionally, a free radical initiator is heated to form a uniform mixture, further subjecting the mixture to high shear mixing conditions sufficient to obtain the polymer having a bimodal molecular weight distribution, produced polymer has a portion having a molecular weight lower than the starting molecular weight of the polymer and a portion having a higher molecular weight than the starting molecular weight of the polymer with proviso that presence of a free radical initiator is optional only in case when the starting polymer is a polymer, capable to form radicals under high shear mixing.  2. The process of claim 1, wherein said mixing step is conducted in the presence of a free radical initiator.  3. The process of claim 2, wherein said polyunsaturated cross-linking agent is a bifunctional compound, containing diallyl, divinyl or diethylenic unsaturated group. 4. The process of claim 2, wherein said polyunsaturated cross-linking agent is selected from the group consisting of polymaleimides, polyallylphosphates, polyallylcyanurates, polyallyl esters of organic acids, polyallylamines; alkyleneglycolpoly(meth)acrylates and polyvinylbenzenes.  5. The process of claim 4, wherein said polyunsaturated cross-linking agent is an organic bismaleimide.  6. The process of claim 5, wherein said polyunsaturated cross-linking agent is a phenylenebismaleimide.  7. The process of claim 2, wherein said free radical initiator is an organic peroxide.  8. The process of claim 7, wherein said organic peroxide is selected from the group consisting of benzoyl peroxide; tert-butylperoxypivalate; 2,4-dichlorobenzoyl peroxide; decanoyl peroxide; propionyl peroxide; hydroxyheptyl peroxide; cyclohexanone peroxide; tert-butylperbenzoate; dicumyl peroxide; 2,5-dimethyl-2,5-di(tert-butylperoxyl)-3-hexyne; 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane; 2,5-dimethyl-2,5-dibenzoylperoxyhexane; tert-butylperoxide; cumene hydroperoxide; 2,5-dimethyl-2,5-di(hydroperoxy)hexane; tert-butylhydroperoxide; lauroyl peroxide and tert-amylperbenzoate. 9. The process of claim 1, wherein said polyunsaturated cross-linking agent is present at a level of from 0.005 to 1.0 millimoles per gram of said polymer.  10. The process of claim 9, wherein said polyunsaturated cross-linking agent level is from 0.01 to 0.5 millimoles.  11. The process of claim 9, wherein said free radical initiator is an organic peroxide present in said composition at a level of from 0.0005 to 0.1 millimoles per gram of said polymer. 12. The process of claim 11, wherein the level of organic peroxide is from 0.001 to 0.05 millimoles.  13. The process of claim 2, wherein said polymer is a statistical copolymer of isobutylene containing up to 20 wt % of polymerized para-methylstyrene. 14. The process of claim 8, wherein said organic peroxide is selected from the group consisting of 2,5-dimethyl-2,5-di(tert-butylperoxyl)-3-hexyne, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide and mixtures thereof. 15. The process of claim 2, wherein said free radical initiator is added to said mixture after step of heating and prior the step of mixing. 16. The process of claim 2, wherein said high shear mixing is conducted for a period of from 1 to 10 minutes. 17. The process of claim 16, wherein said high shear mixing is conducted at a temperature in the range of from 150 degree C to 210 degree C. 18. A process for modifying the molecular weight distribution of a statistical copolymer of isobutylene containing up to 20 wt % of polymerized para-methylstyrene, which produced copolymer has a portion having a molecular weight lower than the starting molecular weight of the copolymer and a portion having a higher molecular weight than the starting molecular weight of the copolymer, and wherein the higher molecular weight portion comprises at least 1.0 wt % of the polymeric material, which process comprises: a) forming a mixture of said copolymer and from 0.05 to 0.5 millimoles per gram of said polymer of a polyunsaturated cross-linking agent;  b) heating said mixture to form a uniform melt mixture; and  c) subjecting said melt mixture to high shear mixing conditions in the presence of an organic peroxide sufficient to obtain a polymer having a bimodal molecular weight distribution.  19. The process of claim 18, wherein said organic peroxide is present in said mixture at a level of from 0.001 to 0.05 millimoles per gram of said copolymer. 20. The process of claim 18, wherein said polyunsaturated cross-linking agent is an organic bismaleimide. 21. The process of claim 20, wherein said organic peroxide is selected from the group consisting of 2,5-dimethyl-2,5-di(tert-butylperoxyl)-3-hexyne, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide and mixtures thereof.  22. A product produced by the process of claims 1, 5 or 18.  23. A polymer composition comprising a polymeric material selected from the group consisting of polypropylene, copolymers of propylene with up to 10 wt % ethylene, polyisobutylene, copolymers of a C4-C7 isomonoolefin with up to 10 wt % isoprene, copolymers of a C4-C7 isomonoolefin with up to 20 wt % of para-alkylstyrene and mixtures thereof, said polymeric material having a number average molecular weight in the range of from 5000 to 5000000, and is characterised as having a bimodal molecular weight distribution containing a lower molecular weight species and a higher molecular weight species, said higher molecular weight species comprising at least 1.0 weight percent of said polymeric material.  24. The composition of claim 23, containing from 1 to 25 weight percent of said higher molecular weight species. 25. The composition of claim 23, wherein said polymeric material has a number average molecular weight in the range of from 10000 to 1000000.  26. The composition of claim 25, wherein said polymeric material is a random copolymer of isobutylene containing up to 20 wt % of polymerized para-methylstyrene.