Studies of network structure of rubber vulcanizates by a cryoscopic method: 4

The freezing-point depression (FPD), ΔT, for unimodal and bimodal end-linked poly(dimethyl siloxane) (PDMS) networks swollen in benzene was measured. The crystal size parameter of benzene in frozen swollen networks, a_H, introduced by Kuhn, which varies inversely as ΔT, was experimentally confirmed to be associated with the screening length and/or the radius of gyration of the network chain in swollen gels by using an expression of power-law type, and to reflect the inhomogeneity of network structure. Further, the values of a_H of bimodal PDMS networks became lower than those of unimodal ones at the same equilibrium concentration of polymer in the swollen networks. Such a tendency was phenomenologically similar to that observed for degraded networks of rubber vulcanizates as compared with undegraded ones. Some discussion with respect to this fact has been carried out on the basis of the origin of FPD.