Synthesis and characterization of dendritic-linear-dendritic triblock copolymers based on poly(amidoamine) and polystyrene

Dendritic-linear-dendritic triblock copolymers composed of linear polystyrene (PSt) and poly(amidoamine) dendrons have been successfully synthesized. Two bromines-terminated PSt with M_n = 13,000 was prepared by atom transfer radical polymerization (ATRP) using α,α′-dibromo-p-xylene as initiator. Then the terminal bromines at both ends of PSt chains were replaced by one imine group of piperazine (PZ), and further Michael addition reaction of terminal PZ with excess 1,3,5-triacryloylhexahydro-1,3,5-triazine (TT) produced the first generation (G₁) of the triblock copolymer. Continuous growth of dendrons from G1.5 to G4 at the both ends of PSt chains was carried out by the iterative Michael addition reactions with excess PZ and following TT. The ABA triblock copolymers composed of the G₁-G₄ dendrons and the linear PSt were obtained. Structures of the triblock polymers were characterized by GPC and ¹H NMR spectra. Thermal phase transitions of the polymers were studied by DSC measurements, and all of the copolymers displayed a glass transition temperature.