RAFT polymerization of diacrylate derivatives having different spacers in dilute conditions

Reversible addition-fragmentation chain transfer (RAFT) polymerization of four divinyl monomers, 1,4-butanediol diacrylate (BDDA) and three poly(ethylene glycol) diacrylates (PEGDAs), were investigated under dilute conditions ([M] = 0.2–0.05 mol/L). RAFT polymerization of BDDA using a dithiocarbamate-type chain transfer agent (CTA) afforded soluble polymers, whereas a cross-linked product was obtained by conventional radical polymerization. The monomer concentration, the nature of the CTA, and the CTA/initiator ratio were found to affect the polymerization behavior and structure of the resulting polymers, which is attributed to the relative propensities for intermolecular propagating/cross-linking reactions and intramolecular cyclization. RAFT polymerizations of three PEGDAs (PEG258DA, average Mn = 258; PEG575DA, average Mn = 575; PEG700DA, average Mn = 700) having different lengths of PEG spacers (n = 3, 10, 13, respectively) were also conducted under dilute conditions. Water-soluble polymers were synthesized by one-step RAFT polymerization of PEGDAs having longer spacers (n = 10 and 13), whereas RAFT polymerization of PEGDA (n = 3) afforded polymers soluble in organic solvents. The product obtained by RAFT polymerization of PEGDA (n = 10) showed a characteristic thermoresponsive property, lower critical solution temperature (LCST), in aqueous solution.