Synthesis of carboxyl-terminated polystyrene and its polycondensation under ambient temperature

Polystyrene with carboxyl-terminated groups was synthesized via a chain-polymerization reaction by the use of styrene as the monomer and 4, 4′-azobis-4-cyanopentanoic acid (ACPA) as an initiator. The effect of proportions among styrene, ACPA and solvent as well as the polymerization temperature on the synthesis of functional polystyrene was investigated. Finally, an amphiphilic block copolymers was prepared by the polycondensation between carboxyl-terminated polystyrene and poly(ethylene glycol) under extremely mild conditions, for instance, ambient temperature and atmospheric pressure. Results from characterizations of Fourier transform infrared spectroscopic (FT-IR) and hydrogen nuclear magnetic resonance spectrum (¹H-NMR) confirms the successful synthesis of the carboxyl-terminated polystyrene and polystyrene-block-poly(ethylene glycol) copolymers. Gel permeation in chromatography (GPC) test indicates that the resulted carboxyl-terminated polystyrene has quite large molecular weight, and the molecular weight distributions are considerably quite narrow. Results from differential scanning calorimetry (DSC) show that the glass transition temperature of the resulting polystyrene enhances gradually with the increase of the molecular weight.