Termination kinetics of acrylate and methacrylate homo- and copolymerizations

Termination kinetics of acrylate and methacrylate homo- and copolymerizations at 40 degreesC and 1000 bar have been measured up to high conversion via the SP-PLP technique. DMPA and alpha-methyl-4-(methylmercapto)-alpha-morpholino propiophenone have been used as photoinitiators. An initial plateau region of constant k(t) is seen which, with MMA, extends up to about 20 monomer conversion and is followed by a reduction in k(t) by about three orders of magnitude up to 50 % conversion. Dodecyl acrylate (DA) shows a distinctly different behavior in that constant (plateau) k(t) is observed up to 75 % conversion. Copolymerization k(t) in the plateau region is adequately described by a penultimate unit effect model. The chain-length dependence of k(t) is investigated for several homopolymerizations using the expression: k(t) = k(t)(0 .) i(-alpha), where i is chain length. With the exception of DA, where alpha is about 0.4 in the entire conversion range, alpha is close to 0.16 in the plateau region and increases once the gel effect region is reached.