Modeling Degradative Chain Transfer in d-Limonene/n-Butyl Methacrylate Free-Radical Copolymerization

Renewable monomers containing allylic C-H bonds in their structure are prone to degradative chain transfer in free-radical polymerization, which will dramatically decrease the polymerization rate. In order to understand this mechanism, a kinetic model incorporating a degradative chain transfer mechanism for the free-radical copolymerization of d-limonene (LIM) and n-butyl methacrylate (BMA) was developed using PREDICI. Model predictions offered insight on how degradative chain transfer reactions affect conversion, copolymer composition and molecular weight in the polymerization. Experimental data from copolymerizations at monomer feed compositions (LIM/BMA, mol/mol) of 10/90, 20/80 and 30/70 were compared to the model's predictions. Moreover, it was discovered that degradative chain transfer results in elevated concentrations of growing polymer chains ending in allylic limonene radicals, which inevitably influences termination reactions and molecular weight development.