Chain Transfer to Polymer in Free-Radical Solution Polymerization of 2-Ethylhexyl Acrylate Studied by NMR Spectroscopy

The effects of initial monomer concentration, Mo, and percent conversion on the extent of chain transfer to polymer in the free-radical solution polymerization of 2-ethylhexyl acrylate (EHA) have been studied. The polymerizations of EHA were carried out in cyclohexane at 70 °C using 2,2′-azobis(2-cyanopropane) at 0.1 wt % relative to monomer as the initiator, 13C NMR spectra of PEHA show that branching resulted from hydrogen abstraction at backbone C-H bonds, with no evidence for chain transfer in the side group. The branching levels were determined from unique resonances of branch-point carbons and ranged from 3 to 8 mol %, increasing as the conversion increased and as Mo decreased. The trends for variation of branching level with Mo and conversion are comparable to those for solution and bulk homopolymerizations of other acrylate monomers and vinyl acetate, although the branching levels for PEHA are much higher than those for poly(n-butyl acrylate) prepared under the same conditions.