Chain transfer to polymer in free-radical solution polymerization of 2-ethylhexyl acrylate studied by NMR spectroscopy

The effects of initial monomer concentration, [M](o), and percent conversio n on the extent of chain transfer to polymer in the free-radical solution p olymerization of 2-ethylhexyl acrylate (EHA) have been studied. The polymer izations of EHA were carried out in cyclohexane at 70 degreesC using 2,2'-a zobis(2-cyanopropane) at 0.1 wt % relative to monomer as the initiator. C-1 3 NMR spectra of PEHA show that branching resulted from hydrogen abstractio n at backbone C-H bonds, with no evidence for chain transfer in the side gr oup. The branching levels were determined from unique resonances of branch- point carbons and ranged from 3 to 8 mol %, increasing as the conversion in creased and as [M](o) decreased. The trends for variation of branching leve l with [M](o) 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 a crylate) prepared under the same conditions.