Mathematical modeling of unsteady state photopolymerization in an isothermal batch reactor has been investigated. An analytical solution of the distribution of active polymers as a function of reaction time has been determined. It is verified that the quasi-stationary state approximation is valid in the photopolymerization process.

The free radical polymerization of styrene is forced periodically by on-off UV light regulation to the reactor. The effect of operating condition, the ratio of light-off period to light on/off period, on the polydispersity and molecular weight distribution are theoretically and numerically investigated. Significant broadening on molecular weight distribution can be obtained during the unsteady state process.

Experimental results of polydispersity are compared to a kinetic model of a nonuniformly initiated photopolymerization, which comprises a high dose rate region and a very low dose rate region. Good agreement is obtained between the model and experiments after fitting three parameters.