Semibatch RAFT copolymerization of acrylonitrile and N-isopropylacrylamide: Effect of comonomer distribution on cyclization and thermal stability

Abstract

Utilizing reversible addition-fragmentation chain transfer (RAFT) polymerization, the composition profile of PAN-based copolymers becomes a tunable parameter in preparing carbon fiber precursors. In this work, poly(acrylonitrile-co-N-isopropylacrylamide) copolymers were prepared via a semibatch process mediated by 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT). The monomer reactivity ratios were determined by the Fineman-Ross (FR), Kelen-Tüdos (KT), and non-linear least squares (NLLS) models. The number average sequence length of acrylonitrile (AN) was found to be highly dependent on the content of N-isopropylacrylamide (NIPAM). NIPAM was introduced at controlled rates into a reaction vessel in attempt to facilitate its distribution in the polymer backbone. These semibatch copolymers were evaluated based on their ring-closing cyclization efficiency, which was characterized by differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Significantly, DSC exotherms were reduced and cyclization occurred much faster reaching a greater thermal stability when NIPAM was introduced at slow feed rates.