Raman Spectroscopic Studies of the Vulcanization of Rubbers. II. Raman Spectroscopic Studies as a Function of Cure Time

It has been demonstrated that Raman spectroscopy can be used to follow changes that occur in the network of vulcanizates as a function of cure time. In the system studied we have found that dialkenyl sulfides, cyclic sulfides and conjugated triene structures parallel the cure. In other words, the Raman lines due to these structures display an asymptotic trend as a function of cure time with the plateau occurring in the region of the optimum cure time. On the other hand those Raman lines assigned to the trans isomer and conjugated dienes do not exhibit the same asymptotic dependence as a function of cure time but show an increase in intensity as the cure time is prolonged up to at least 2 hours at 150° C. This would appear to indicate that these Raman lines are not solely associated with the vulcanization process but that thermal and allied processes may contribute. The Raman line occurring at 440 cm−1 does not show any definitive trend and is unlikely to be associated directly with the network. It is most probably due to unextracted extra-network ZnO present.