Synthesis of hyperbranched-linear star block copolymers by atom transfer radical polymerization of styrene using hyperbranched poly(siloxysilane) (HBPS) macroinitiator

Hyperbranched-linear star block copolymers, hyperbranched poly(siloxysilane)-block-polystyrene (HBPS-b-PSt), were prepared by atom transfer radical polymerization (ATRP) of styrene in xylene, using bromoester-terminated HBPS (HBPS-Br (P3), Mn = 7500, Mw/Mn = 1.76) as a macroinitiator. The number-average molecular weights of the obtained polymers (Mn) were in the range of 21,800–60,000 and molecular weight distributions were unimodal throughout the reaction (Mw/Mn = 1.28–1.40). These polymers showed 5 wt.% decomposition temperature (Td5) over 300 °C. The DSC thermograms of the resulting polymers indicated two glass transition temperatures (Tg). The Tg of HBPS segment shifted to higher value while the Tg of PSt segment shifted to lower value compared with those of the homopolymers. Preliminary physical characterization related to the solution viscosity of the resulting block copolymers is also reported.