A detailed on-line FT/NIR and 1H NMR spectroscopic investigation into factors causing inhibition in xanthate-mediated vinyl acetate polymerization

Potential sources of inhibition have been investigated via in situ Fourier transform - near infra-red (FT-NIR) and off-line H-1 NMR spectroscopy in the RAFT/MADIX bulk polymerization of vinyl acetate (VA) in the presence of an O-isopropyl xanthate, i.e. methyl (isopropoxycarbonothioyl)sulfanyl acetate. The very high reactivity of the vinyl acetate propagating radical makes it very vulnerable to oxygen, by-products generated during the xanthate synthesis, and stabilizers present as impurities. These impurities induce strong and variable inhibition periods in the polymerization. In addition, the MADIX process, using xanthates as reversible chain transfer agents, has been confirmed to be an efficient method for living VA polymerization. Congruent data are obtained when the monomer consumption with time is followed via both H-1 NMR and in situ FT-NIR spetroscopy. The xanthate-mediated polymerization of VA exhibits no retardation effects and excellent control of the molecular weight distribution can be achieved, leading to poly(VA) of molecular weights exceeding 50 000 g . mol(-1) with relatively low polydispersities.