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

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 degrees 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-pentamethyldiethylenetriamine (PMDETA) catalyst system. In some cases, the ester side chains of the poly(tert-butyl acrylate) (PtBA) blocks were cleaved to create poly(acrylic acid) (PAA) blocks. The final miktoarm star polymers had compositions that were very close to theoretical. (c) 2008 Elsevier Ltd. All rights reserved.