Glass Transition Temperature of Cyclic Stars

Cyclic homo- and diblock copolymers with different topologies were synthesized using a combination of living radical polymerization and click coupling reactions. The topologies included 2- and 3-arm stars, with the arms consisting of either cyclic or linear polystyrene. In addition, a diblock consisting of a cyclic polystyrene and a cyclic poly(acrylic acid) was also made. The topologies by imposing topological constraints due to the presence of cyclic polymers and branch points had a marked influence on the glass transition temperature (T-g. It was found that for the polystyrene topology series, the T-g increased above the glass transition temperature at infinite molecular weight for a linear chain (i.e., T-g(infinity)) and correlated to the more compact nature of cyclic polymers. For the cyclic diblock of polystyrene and poly(acrylic acid), the T-g increased significantly due to separation of the blocks into their pure phases. This resulted in significant stretching of the chains and thus loss of conformation entropy.