In-situ NMR spectroscopy for probing the efficiency of RAFT/MADIX agents
The experimental evidence of selective initialization of poorly stabilized monomers in reversible addition fragmentation chain transfer (RAFT) mediated living radical polymerization was reported. Xanthate chain transfer agents (CTA) were used to mediate the polymerization of N-vinylpyrrolidone (NVP) and vinyl acetate (VAc). In-situ H NMR spectroscopy was performed to follow the concentrations of xanthate and monomer and to identify the nonradical species in the RAFT mechanism. Various xanthates were screened and a direct relationship between a xanthate-monomer system which gives fast and selective initialization and a high degree of control over the molar mass distribution of the polymer was found. The results show that in-situ H NMR spectroscopy can quantitatively probe the mechanism of initialization involved in the transformation of a CTA into a dormant oligomeric chain.