Photocuring and Photopolymerization Investigations

Curing by light irradiation can be apphed to a variety of polymers. The acrylic family is a typical example of photosensitive monomers. A well-documented review has recently been dedicated to the curing of composites by ultraviolet radiation [45], Photocuring time is much shorter than for traditional thermal curing (minutes rather than hours), leading to a significant reduction in the cycle time. 

minutes. Reproduced from reference [50], (c) 2001 with permission from the American Chemical Society. 

The authors explained the observed temporary cessation of heat release by the difference between the rate of polymer formation and that of volume relaxation. According to their observations, the difference between the two phenomena leads to a situation in which the free radicals are spatially separated from the unreacted VA molecules. The subsequent spatial relaxation brings them into contact and the reaction starts again. 

The same authors used photoDSC to obtain time- or conversion-dependent ratios of the termination and propagation rate coefficients 2kt/kp for the polymerization of VA. The starting point of this approach is the classical equation derived from formal kinetics  

The rate of polymerization is assumed to be equal to the ordinate of the DSC trace, dQJdt [51]. At each time t, the concentration of the remaining monomer is proportional to (Q - Q), with Q corresponding to the total heat released when the photopolymerization is completed (% = 100%). Equation 10.8 can then be written as follows  

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