Monomolecular and bimolecular termination in the polymerization of di(meth)acrylates

The termination mechanism in the polymerization of a series of analogous di(meth)-acrylates differing only by the type of the heteroatom (S or O) in the ester group was investigated. The experimental method was based on differential scanning calorimetry measurements of photochemically initiated polymerization. The ratio of the bimolecular termination and propagation rate constants k/k_p and/or the monomolecular termination rate constant k were determined according to three termination models (monomolecular, bimolecular, and mixed). Statistical techniques were used for choosing between the models to find out by which mechanism (monomolecular, bimolecular or mixed) the termination occurs. The results obtained prove than monomolecular reaction is an important termination way in the polymerization of multifunctional monomers and must be taken into account when kinetic constants are determined, even at low degree of conversion. The sulfur-containing monomers are characterized by much lower k values than the analogous sulfur-free monomers.