Modeling the polymerization kinetics of a dimethacrylate monomer in the after-effect period.
Polimery 2001, No 10, 721
SummaryIsothermal differential scanning photocalorimetry was used to monitor the light-induced (366 nm; 1.3 mW/cm2; 40oC, Ar atm.) polymerization of (diethylene glycol) dimethacrylate proceeding in the presence of 0.03 M 2,2-dimethoxy-2-phenylacetophenone and to study variations in the mechanism of termination in the after-effect period after illumination had been discontinued. Illumination was stopped at five moments of the reaction corresponding to different degrees of double bond conversion. Three termination models, mono [I, eq. (1)], bimolecular [II, eq. (2)], and mixed type [III, eq. (3)], were used to evaluate parameters ktm and kp[P]0; ktb[P]0 and kp[P]0; and ktm, ktb[P]0 and kp[P]0, resp., where ktm and ktb are the mono and the bimolecular termination rate coefficients, kp is the propagation rate coefficient and [P]0 is the macroradical concentration at the start of the dark reaction. The parameters were calculated at various durations of postpolymerization (10-160 s at 10-s increments) starting invariably at the moment of discontinuation of illumination. In this manner, the propagation and termination rate coefficients were averaged over increasingly large dark conversions. Two-stage statistical analysis was used to find the "best" model. Termination was found to follow the mechanism varying with time of dark reaction from the bimolecular to the mixed type, whereby radical trapping is seen to be increasingly important. Model III was the only model to describe correctly the variation of the dark reaction rate coefficients with time, i.e., the increase in ktm and decrease in the product ktb[P]0.