Controlled radical polymerization of cholesteryl acrylate and its block copolymer with styrene via the RAFT process

Abstract

Reversible addition fragmentation chain transfer (RAFT) polymerization of cholesteryl acrylate (ChA) was conducted using S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate as CTA and AIBN as initiator in toluene at 80 °C. The polymerization was investigated at two different CTA concentrations (0.025 and 0.040 M). Polymerization of ChA with CTA concentration of 0.040 M proceeds in a controlled/living manner as evidenced by linear increase of the molecular weight with conversion and narrow polymer polydispersity (PDI < 1.2). With lower initial CTA concentration, namely 0.025 M, although poly(cholesteryl acrylate) (PChA) exhibiting narrow molecular weight distributions could be synthesized, the polymerization showed relatively low control with many termination products. Chain extension polymerizations were performed starting from either the PChA or the polystyrene (PS) block, and well-defined copolymers based on ChA and styrene were prepared. Thermal properties of PChA and PS- b-PChA copolymer were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the results showed that both PChA and PS- b-PChA are amorphous polymers. PChA begins to decompose at ca. 218 °C with maximum weight loss rate at 351 °C, while PS- b-PChA shows double weight loss rate peaks located at 345 and 415 °C, respectively.