Synthesis and Characterization of Model Cyclic Block Copolymers of Styrene and Butadiene. Comparison of the Aggregation Phenomena in Selective Solvents with Linear Diblock and Triblock Analogues

Abstract

The synthesis and characterization of model cyclic diblock copolymers of styrene (St) or perdeuterated styrene (St-d8) and butadiene (Bd) are presented. Since conventional methods of characterization cannot separate completely the cyclic copolymer from its linear precursor, differences in the micellar behavior were used as a method for investigation of their purity. For this purpose, in addition to the cyclic and linear triblock copolymers, two linear diblocks with similar compositions, and molecular weight equal or half of the cyclic diblocks, were also synthesized. The synthetic approach of the cyclics involved the reaction of (1,3-phenylene)bis(3-methyl-1-phenylpentylidene)dilithium initiator with butadiene in the presence of sec-BuOLi, followed by polymerization of St (or St-d8). The cyclization of the resulting α,ω-difunctional triblock copolymer was performed by using bis(dimethylchlorosilyl)ethane, under high dilution conditions. The copolymers were characterized by size exclusion chromatography, m...