Domain bridging in thermoplastic elastomers of star block copolymer

Abstract

The performance of thermoplastic elastomers composed of block copolymers is dependent upon the molecular bridges linking together the discrete minority domains. Here we devise a strategy for calculating the bridging statistics for complex block copolymer architectures, using self-consistent field theory. The method is demonstrated on (AB)_M stars with M identical diblock arms. The fraction of molecules forming bridges, nu_b, is found to increase rapidly with M to values well beyond that of conventional ABA triblock copolymers. Once M is of order 10, virtually all molecules form bridges and furthermore their arms tend to be distributed equally among neighboring minority domains. These high bridging fractions combined with the tendency of single molecules to bridge multiple domains makes diblock-arm stars an excellent candidate for improved thermoplastic elastomers.