Allylic monomers as reactive plasticizers of polyphenylene oxide. Part II: Cure kinetics

As part of an investigation of the processing of polyphenylene oxide (PPO) with polymerisable plasticizers, the curing kinetics of various diallylic monomers – diallyl ortho phthalate (DAOP), diallyl terephthalate, triethylene glycol diallyl ether and diethylene glycol diallyl carbonate) – and triallylic – triallyl cyanurate and triallyl isocyanurate – with radical initiators of differing activity were studied. All the monomers exhibited similar cure kinetics with each initiator and the exotherm peak temperatures correlated well with the reactivity of the initiators as measured by the 1 h half-life temperatures. Multiple scan-rate dynamic DSC studies gave similar activation energies to those obtained from isothermal rheology studies of gelation. The effects of the presence of PPO on the curing of diallyl ortho phthalate (DAOP) were studied using dicumyl peroxide (DCP) and tert-butyl hydroperoxide (TBHP) as initiators and differing behaviour was observed. In the PPO:DAOP/DCP system, the reaction rate was reduced with increasing PPO due to a dilution effect but the heat of reaction was generally unaffected. However, in the PPO:DAOP/TBHP system, a significant increase of cure rate was observed in the presence of 20 wt.% PPO due to the catalysis of TBHP by Cu2+ and Co3+ impurities in the PPO, but the cure rate was slightly reduced with increasing PPO content. In addition, the heat of polymerisation for the PPO:DAOP/TBHP blends were usually less than that for the pure monomer. This information can be used in the processing of PPO with DAOP as a polymerisable plasticizer.

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► We have examined the effect PPO on the polymerisation of DAOP with various radical initiators.
► The cure kinetics of the allylic monomers were similar, as were the activation energies, when the same initiator was used.
► The heat of reaction for polymerisation depends on the allylic monomer and the reactivity of the initiators.
► Addition of PPO to DAOP reduced the polymerisation rate of DAOP with DCP initiator due to dilution effect.
► Copper and cobalt impurities in PPO increase the polymerisation rate of DAOP with TBHP initiator.