Effects of alkylation of silicas on interfacial interaction and molecular motions between silicas and rubbers

The interactions between rubbers and silicas were studied by means of bound rubber determination, vulcanizate swelling procedure, and tensile retraction measurement. The mobilities of rubber chain segments in mixture with silicas were investigated by thermomechanical and dynamic mechanical analyzers. The results show that when the untreated silica was incorporated into rubbers, the strong interaction of rubber with the silica apparently constrains the segmental motions of the rubber molecules, resulting in the decrease in the dynamic loss peak and the thermal expansion coefficient, and the increase in the glass transition temperature. The alkylations on silica surfaces weaken the interfacial interaction between rubbers and silicas, and the mobilities of the rubber molecules become less restricted. Furthermore, proton spin-spin relaxation time (T-2) measurements by the pulsed NMR on the insoluble bound rubber, indicate that there are two relaxing regions: an immobile (or a tight) region and a relatively free (Or a loose) one. The types of the rubbers and the activities of the silica surfaces have influences on the relaxation process of the two bound rubber components. (C) 1996 John Wiley & Sons, Inc.