KINETICS OF ANISOTROPIC PHOTOPOLYMERIZATION IN POLYMER MATRIX

The photopolymerization mechanism is investigated in films consisting of a rigid plasticized polymeric matrix, photoinitiator and monomer. These photopolymers are widely used commercially in electronics, printing and holography. Illumination, typically from one side, initiates a chemical sequence that records the incident light pattern in the polymer. A method developed in our laboratory is employed to monitor the course of reaction. The photopolymerization rate and yield vary greatly with the distance from the film surface because of the high optical density of the film and the presence of oxygen. Monomer and oxygen migrate towards the illuminated surface of the film where most of the excitation and reagent consumption takes place. Thus the unidirectional illumination creates a spatially anisotropic distribution of reactants and products. A semiempirical computer model of the spatial dependence of photopolymerization kinetics is presented. Photopolymerization kinetics are studied as a function of film thickness, light intensity and rate of monomer diffusion. Calculations explain the experimentally observed kinetics and predict the time dependence of the polymer distribution in the film.