Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations

摘要

Poly(isobutylene-b-styrene)(PIB-PS)copolymers and polyisobutylene(PIB)homopolymers were synthesized via quasiliving carbocationic polymerization from the initiator 3,3,5-trimethyl-5-chlorohexyl acetate,which contains a protected hydroxyl group.The PIB block was created at-70°C in a methylcyclohexane/methyl chloride(60:40)cosolvent system,using TiCl4 as co-initiator,followed optionally by sequential addition of styrene.Using a strong base,the acetate head group of the resulting block copolymer was cleaved to yield a hydroxyl group,which was subsequently esterified with the branching agent 2,2-bis((2-bromo-2-methyl)propionatomethyl)propionyl chloride(BPPC)to create dual initiating sites for atom transfer radical polymerization(ATRP).ATRP of tert-butyl acrylate was carried out using a Cu(I)Br/1,1,4,7,7-penta-methyldiethylenetriamine(PMDETA)catalyst system.In some cases,the ester side chains of the poly(tert-butyl acrylate)(PrBA)blocks were cleaved to create poly(acrylic acid)(PAA)blocks.The final miktoarm star polymers had compositions that were very close to theoretical.