Polymerization Catalysis and Kinetics

Transition metal organometallic complexes like dicarbonyl cyclopentadienyl iron [128], tricarbonyl cyclopentadienyl manganese [129] and iron-arene complexes [130,131] have also been reported as photoinitiators for photochemical crosslinking of cyanate esters. Photosubstitution of carbonyl groups by -OCN during irradiation initiates the reaction in the former case whereas photochemical dissociation of arene triggers it in the latter system. 

Earlier studies attributed first-order kinetics to the reaction, based on evidence from on-line IR and DSC analysis [116], the reaction presumably being induced by phenolic impurities. The deviation from mean field theory is attributed to diffusional limitations, which is more prominent in CEs with rigid backbone. 

A better empirical kinetic model consisting of two parallel, second order competing reactions, one of which is autocatalytic towards the dicyanate, was proposed by Simon and Gillham [93] for the uncatalyzed reaction. 

Other researchers have also successfully applied the autocatalytic model [122, 134]. For fitting the conversion-time curves in this context, the conversion can be indirectly obtained from the Tg of the partly cured matrix. Georjon et al. [122] studied the evolution of Tg with cyanate conversion in the isothermal cure of un- 

The Tg of a partially cured network is originally given by the DiBenedetto s equation [135] as 

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