Latent Amine Cures of Brominated Poly(isobutylene-co-isoprene)
Faba, Michael A.J.
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The allylic bromide functionality within brominated poly(isobutylene-co-isoprene), or BIIR, alkylates primary amines repeatedly to generate thermoset products at reaction rates that are too fast to support commercial rubber processing operations. The objective of this work was to assess the utility of latent N-nucleophiles as curatives and modification reagents for BIIR. Ideally, BIIR formulations containing these latent amines would not cure at standard compound mixing temperatures, but support high crosslinking rates and yields upon heating to conventional vulcanization temperatures. Carbon dioxide-derived salts of ammonia, including (NH4)2CO3, (NH4)HCO3 and (NH4)H2NCO2, can be mixed with BIIR without incurring crosslinking at temperatures below 100oC, but they generate adequate crosslink yields upon heating to 160oC. The corresponding CO2-derived salts of primary amines decompose below 100oC and, therefore, do not provide adequate scorch protection when mixed with BIIR. Latency was conferred on primary amines using imine derivatives, in particular N-alkylbenzaldimine and its substituted analogues. These latent curatives are activated by hydrolysis, thereby providing a means of controlling active nucleophile concentrations, and minimizing crosslinking activity at 100oC without impacting negatively on cure rates at 160oC. The scorch problems generated by primary amines extend to BIIR cure formulations employing conventional sulfur and ZnO curatives. In contrast, imine analogues are shown to provide low temperature scorch stability without impacting negatively on high temperature cure rates and extents.