Copolymerization of isoprene and hydroxyl containing monomers by controlled radical and emulsion methods

Abstract

Polyisoprene (PI) with pendent hydroxyl groups was synthesized by the radical copolymerization of isoprene and the hydroxyl containing comonomers 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), and methylenebut-3-en-1-ol (IOH). The reversible addition–fragmentation chain transfer (RAFT) controlled radical copolymerizations of isoprene with these comonomers were carried out at an initial hydroxyl mole fraction (f_OH) of 0.03 in the bulk at 125 °C. Aliquots of the polymerizing reaction solution indicated that copolymerization competed with the Diels–Alder reaction between the hydroxyl monomers and isoprene as well as the Diels–Alder homodimerization of isoprene. Significantly more IOH comonomer was incorporated into the copolymer (39 mol%) than either HEMA (23 mol%) or HEA (3 mol%). Furthermore, IOH polymerized at a rate similar to isoprene, which coupled with the slower Diels–Alder reaction resulted in hydroxyl functionalized copolymers with a more even distribution of comonomers. Additionally, only IOH copolymerized with isoprene under emulsion conditions at 25 °C due to its limited solubility in water. The isoprene/IOH emulsion copolymers had hydroxyl monomer content close to f_OH at complete monomer conversion. The utility of the hydroxyl functionalized PI was demonstrated by using it as a macroinitiator for the ring opening polymerization of D,L-lactide, yielding microphase separated polylactide graft polymers.