In situ 1H NMR studies of high-temperature nitroxide-mediated polymerization of n -butyl acrylate
This paper presents results on the independence of the rate of polymerization of n-butyl acrylate (n-BA) toward initial concentration of the alkoxyamine initiator. The alkoxyamine, 2-methyl-2-[N-tert-butyl-N-(1- diethoxyphosphoryl-2,2-dimethylpropyl)aminooxy]propionic acid (MAMA-DEPN), was used to initiate and mediate the polymerization of n-BA in the temperature range 90-120 °C. In situ1H NMR spectroscopy was used to follow the consumption of the monomer and monitor other related reactions. Intra- and intermolecular chain transfer processes are well-known phenomena in the polymerization of n-BA that result in the transformation of secondary propagating radicals (SPRs) into tertiary midchain radicals (MCRs). At high polymerization temperature (T ≥ 110 °C), the MCRs undergo β-fragmentation. The concentrations of the products of the β-fragmentation process (in the form of chains bearing 1,1-disubstituted alkene end group) were measured as a function of polymerization time. The independence of rate of polymerization of n-BA initiated by MAMA-DEPN can be explained in terms of thermal autoinitiation in the case where free [DEPN] 0 is no larger than 1 mol % relative to [MAMA-DEPN]0. © 2011 American Chemical Society.