Study of the RAFT polymerization of a water-soluble bisubstituted acrylamide derivative. 1. Influence of the dithioester structure

Homopolymers of N-acryloylmorpholine (NAM), a water-soluble bisubstituted acrylamide derivative, have been synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT)., Several dithioesters were used as chain transfer agents: carboxymethyl dithiobenzoate (CMDB), tert-butyl dithiobenzoate (tBDB), menthonyl dithiobenzoate (MDB), and a bifunctional dithiobenzoate, 1,3-bis(2-(thiobenzoylthio)prop-2-yl)benzene (TPB). Whereas CMDB is a commercial reagent, tBDB and MDB were synthesized by a novel biphasic process based on a thioacylation reaction and leading to very high, yields. The performances of the four dithiobenzoates were compared in term of kinetics and molecular weight,distribution control. Very good control of NAM polymerization was obtained with tBDB and MDB, with a linear increase of M-n vs conversion over the whole conversion range and with polydispersity indices (PDI) below 1.1, as determined by aqueous size exclusion chromatography with on-line light scattering detection. In addition, a degradation phenomenon of the dithioester. functions was evidenced during the course of the polymerization, correlated with a M. vs conversion curve leveling off and even sometimes decreasing above 80% conversion. Such observations were assumed to be the consequence of the formation of side products in-the polymerization media, subsequently acting as nondegradative irreversible transfer agents.