CURE KINETICS OF LIGHT-ACTIVATED POLYMERS

The purpose of this article is to develop a mathematical model that de scribes photocure and photopolymerization kinetics. This model is neit her wholly phenomenological nor mechanistic, but contains elements of both. We draw an analogy between the classical Avrami approach for fir st-order phase transformations and the kinetic phenomena that occur du ring photocuring, and take into account cure inhibition due to a decre ase in mobility of the constituents. The result is an explicit algebra ic two-parameter expression for the extent of cure versus time. More i mportantly, the two parameters have physical significance, and to some extent can be predicted a priori. The model is compared to three sets of unrelated data, and excellent agreement is obtained, except for pa rt of the data at the onset of the reactions. Physical insight obtaine d by comparing our theory with experiments supports the existence of p referred sites for initiating the reaction, and indicates that irradia tion is the rate-limiting step in the overall cure process in the limi t of small irradiation intensities. (C) 1998 John Wiley & Sons, Inc.