Modelling the Kinetics of Photoinitiated Polymerization of Di(meth)acrylates

The kinetics of photoinitiated polymerization of six analogous di(meth)acrylates and diacrylates was analysed according to the autocatalytic model Rp=kpm(1-p)n (where Rp is polymerization rate, p is conversion degree, k is reaction rate constant and m and n are exponents), in order to find the influence of the reaction temperature and atmosphere, as well as monomer structure, on the parameters k, m and n. The best fit between the model prediction and experimental data was for the polymerization of diacrylates in an inert gas atmosphere. The autocatalytic exponent, m, for polymerization in argon of both di-methacrylates and diacrylates was found to be close to unity, whereas the reaction order exponent, n, was twice as high for the former compared with the latter (in the range of c. 3–5 and c. 1·3–2, respectively). An increase in the polymerization temperature caused a drop in both exponents. This drop is much more rapid in the case of the exponent n. Changes in the m and n exponents with temperature, as well as the difference in n exponents for the polymerization of acrylates and methacrylates, may be related to changes and differences in the mobility of reactive species during the reaction. The influence of atmospheric oxygen on the polymerization parameters is manifested by a very high increase in value of the exponent n. In the photochemically initiated process, an increase in the polymerization rate with temperature results mainly from a rapid decrease in the exponent n and, to a much lesser degree, from an increase in the reaction rate constant k.