Effect of branching architecture on glass transition behavior of hyperbranched copolystyrenes: the experiment and simulation studies

Abstract

By controlling the feed ratio of CMS/styrene and the polymerization time, a series of hyperbranched copolystyrenes (HBCPS) were synthesized with comparable weight-averaged molecular weights (M w) but different degree of branching (DB) through atom transfer radical self-condensing vinyl copolymerization (ATR-SCVCP) with CuBr/2,2′-bipyridyl as the catalyst. The resulting HBCPS samples were used to investigate the effect of branching architecture on their glass transition behavior. With the DB increased, the glass transition temperatures (T g) of HBCPS samples measured by DMA and DSC both decreased. Their spin-lattice relaxation times (1H T 1r) of protons displayed the same downtrend with increasing DB. Besides, a correlation between the T gs and the DB was well established by all-atom molecular dynamics (MD) simulations. The values of MD-determined T gs are little higher than the corresponding experimental ones. However, the dependence of T gs on DB is in good agreement with the experimental results, i.e., T g decreases both in experiments and simulations with increasing DB.