Correlation of the Extent of Chain Transfer to Polymer with Reaction Conditions for Emulsion Polymerization of n-Butyl Acrylate

Chain transfer to polymer in emulsion polymerisation of n-butyl acrylate has been studied. Branch points in the structures of the polymers formed have been identified by 13C NMR spectroscopy and reveal that branching results from intermolecular chain transfer reactions in which a propagating chain radical abstracts a hydrogen atom from a tertiary C-H bond in an n-butyl acrylate repeat unit on another polymer chain. Under the usual conditions of high instantaneous monomer conversions, this reaction leads to polymers with high extents of branching (10-20 branches per 1000 backbone carbon atoms). The effects of polymerisation conditions upon the extent of branching are discussed, and changes in molar mass distribution during emulsion polymerisation are correlated with observations on the extent of chain transfer to polymer.