SYNTHESIS OF POLY(ISOBUTYLENE-B-METHYL METHACRYLATE) COPOLYMERS BY THE COMBINATION OF LIVING CARBOCATIONIC AND GROUP-TRANSFER POLYMERIZATION

Poly(isobutylene-b-methyl methacrylate), p(IB-b-MMA), copolymers were synthesized by reacting the two corresponding living homopolymers, obt ained by living carbocationic and group transfer polymerization, respe ctively. IB was polymerized by the 2,4,4-trimethyl-2-chloropentane (TM PCl)/TiCl4/methylcyclohexane:CH3Cl 60:40 v:v/-80 degrees C system. Whe n the polymerization was complete, 1,1-diphenylethylene was added to c onvert PIB-Cl to the corresponding diphenylcarbenium ions. To this sol ution living PMMA, obtained by group transfer polymerization, isolated and dissolved in CH3Cl was added, and the reaction mixture was allowe d to warm to -40 degrees C. Depending on the livingness of PMMA, up to 80% coupling efficiency could be obtained. It was found that at -40 d egrees C after reaching a maximum of similar to 80% the coupling effic iency decreases with time. In a very slow competitive reaction, the fo rmed block copolymers are cleaved by a mechanism suggested to involve the complexation of TiCl4 to the carbonyl oxygen adjacent to the coupl ing site, followed by anion formation and irreversible termination. Th is side reaction can be minimized by limiting the reaction time to <4 h at -40 degrees C and by using a low [TiCl4]/[TMPCl] = 4 ratio.