N-(morpholinothio)imides as curing agents in semiefficient vulcanization systems



Semiefficient vulcanization systems (semi-EV) are often used when a stock requires good aging properties as well as good fatigue resistance. A partial replacement of sulfur in a conventional cure system with 4,4′-dithiobismorpholine or 2-mercaptabenzothiazyl 4-morpholino disulfide (BMD) is an example of semi-EV system. However, with BMD the scorch time is not always long enough for multisteps involved in the manufacturing of tires. Such new cure retarders as N-(cyclohexylthio)phalimide or N, N′-bis(cyclohexylthio)oxanilide showed very little efficiency in BMD cure systems. This paper describes the usage of new curing agents, (N-morpholinothio)imides, which can overcome the disadvantage of scorchness in BMD cure system and provide excellent aging properties. This is rationalized by the formation of BMD during vulcanization. The facile formation of BMD from N-(4-morpholinothio)phthalimide (MTP) and 2-mercaptobenzothiazole (MBT) serves to illustrate the feasibility of in situ formation of BMD during cure and to explain long scorch time observed with N-(4-morpholinothio)imides.