LIVING COUPLING REACTION IN LIVING CATIONIC POLYMERIZATION - 2 - SYNTHESIS AND CHARACTERIZATION OF AMPHIPHILIC A(2)B(2) STAR-BLOCK COPOLYMER - POLY[BIS(ISOBUTYLENE)-STAR-BIS(METHYL VINYL ETHER)]

Amphiphilic A(2)B(2) star-block copolymers (A = polyisobutylene (PIB) and B = poly(methyl vinyl ether) (PMeVE)) have been prepared via the l iving coupling reaction of living PIE, using 2,2-bis[4-(1-tolylethenyl )phenyl]propane (BDTEP) as a living coupling agent, followed by the ch ain ramification reaction of methyl vinyl ether (MeVE) at the junction of the living coupled PIE. Model reactions for the synthesis of A(2)B (2) star-block copolymers indicated that the fine-tuning of Lewis acid ity to the reactivity of MOVE is a crucial step for the structural int egrity of the resulting A(2)B(2) star-block copolymers. Side products were negligible using a [Ti(OEt)(4)]/[TiCl4] ratio of 0.7 and the mini mum tuning time (similar to 5 min). Fractionation of the crude A(2)B(2 ) star-block copolymer was carried out on a silica gel column, and on the basis of the weights of fractions, the purity of the crude A(2)B(2 ) star-block copolymer was calculated to be greater than or equal to 9 3.5%. Two T(g)s (-60 degrees C for PIB and -20 degrees C for PMeVE) we re observed for the star-block copolymer by DSC indicating the presenc e of two microphases. An A(2)B(2) star-block copolymer with 80 wt % PM eVE composition ((IB45)(2)-s-(MeVE170)(2)) exhibited a critical micell e concentration (cmc) of 4.25 x 10(-4) M in water, which is an order o f magnitude higher than cmcs obtained with linear diblock copolymers w ith same total M-n, and composition (IB90-b-MeVE340) or with same segm ental lengths (IB45-b-MeVE170) This suggests that block copolymers wit h star architectures exhibit less tendency to micellization than their corresponding linear diblock copolymers. Average particle sizes in aq ueous solution above the cmc were measured to be from 41 to 177 nm, de pending on the architecture and/or the molecular weight.