MATRIX INHOMOGENEITY IN CROSS-LINKED RUBBER AND RUBBER EMULSIONS

The radiation induced crosslinking of a polymer can be greatly affected by its environment and morphology. This is examined for rubber of identical source, but irradiated as (1) nonpurified, (2) purified rubber and (3) as an emulsion where the rubber particles are separated. Measurements include solubility, swelling and ESR studies using spin probe whose penetration into the denser parts of rubber network can be inhibited in the more crosslinked form. An apparent discrepancy between solubility and swelling data in irradiated emulsion is ascribed to a bimodal structure in the rubber emulsion, with dense rubber particles linked together by more extended chains. The use of spin probe technique allows an estimate of the penetrability of these small molecules in both irradiated latex emulsion and dry latex. The slow component of the ESR spectra is ascribed to spin probes in regions of high crosslink density, whereas the fast component is identified with spin probes in lightly crosslinked regions. According to the ratio of slow and fast ESR component latex irradiated in emulsion reveals different morphology as compared with the irradiated dry latex.