Macromolecular design via the interchange of xanthates (MADIX): Polymerization of styrene with O-ethyl xanthates as controlling agents

Control of the free-radical polymerization of styrene was achieved using a series of eight xanthates of the general structure R-A(C=A)OEt as reversible addition fragmentation chain-transfer agents. The influence of the nature of the R leaving group was explored. It was found that the transfer ability of the xanthate is markedly improved with increasing stability of R and its steric hindrance. Group R strongly influences the M-n evolution profile during polymerization, but only influences the polydispersities to a small extent. The cyanoisopropyl group was shown to be the best leaving group, leading to an increase in the molecular weight during polymerization that was close to linearity. The living character of the polymerization and the high purity of the chain structures were supported by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and C-13 NMR spectroscopy. A zero-order dependence of the kinetics of polymerization on the xanthate concentration was observed.