Abstract
The syntheses of thermal latent catalysts have been carried out by modifying the substituent of pyrazinium salts. The thermal latent properties and cure behaviors of difunctional epoxy resin (diglycidylether of bisphenol-A, DGEBA) with 1 wt% of catalyst as an initiator were investigated by dynamic DSC method. As a result, the synthesized catalysts showed the good latent thermal properties in epoxy system. With increasing the basicity of substituted catalyst, the cure temperature and activation energy of epoxy system were increased, whereas the activity was decreased. This was probably due to the fact that the activity and cure behavior were controlled by ring strain and basicity of substituent. Consequently, the catalyst activity modified by methyl group as an electron donor was decreased in increasing of basicity in an initiation step of epoxy cure system. This is due to a decreasing of stabilities of both leaving group of pyrazinium salts and benzyl cation. However, the catalyst activity modified by cyano group as an electron acceptor was increased in increasing the stability of benzyl cation resulting from organic effects and resonance.
피라진염의 치환기를 변화시킨 열잠재성 양이온 촉매를 합성하고, 이관능성 에폭시(diglycidylether of bisphenol-A, DGEBA)에 개시제로서 1 wt% 촉매를 혼합하여 동적 DSC방법을 이용한 경화 거동과 열잠재 특성에 대해 연구하였다. 그 결과 합성된 촉매들은 에폭시 시스템에서 우수한 열잠재성을 가지고 있음을 확인하였다. 치환기의 염기도(basicity)가 높을수록 경화온도와 활성화 에너지는 높아지고 활성은 낮아졌는데 이는 활성과 경화거동이 링 스트레인(ring strain) 및 도입된 치환기의 염기도(basicity)에 의해 조절되기 때문인 것으로 사료된다. 결론적으로, 전자공여 그룹인 메틸기를 도입한 촉매의 활성은 경화시 개시단계에서 염기도 증가로 인한 피라진의 이탈능과 벤질 양이온의 안정성이 감소되었기 때문에 낮아졌으며, 전자수용 그룹인 시아노기를 도입한 촉매의 활성은 유기효과와 공명에 인해서 벤질 양이온의 안정성이 증가됨으로써 높아졌다.
