MODELING 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 R(p) = kp(m)(1 - p)(n) (where R(p) is polymerization rate, p is conversion degree, k is reaction rate constant and m and n are expone nts), in order to find the influence of the reaction temperature and a tmosphere, as well as monomer structure, on the parameters k, m and n. The best fit between the model prediction and experimental data was f or the polymerization of diacrylates in an inert gas atmosphere. The a utocatalytic exponent, m, for polymerization in argon of both dimethac rylates and diacrylates was found to be close to unity, whereas the re action order exponent, n, was twice as high for the former compared wi th the latter (in the range of c. 3-5 and c. 1 . 3-2, respectively). A n increase in the polymerization temperature caused a drop in both exp onents. This drop is much more rapid in the case of the exponent n. Ch anges in the m and n exponents with temperature, as well as the differ ence in n exponents for the polymerization of acrylates and methacryla tes, may be related to changes and differences in the mobility of reac tive 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 mainl y from a rapid decrease in the exponent n and, to a much lesser degree , from an increase in the reaction rate constant k.