Study of matrix inhomogeneity of natural rubber and synthetic polyisoprenes by a spin probe method

Abstract

Nitroxide spin probes have been used to investigate the matrix morphology of natural rubber (NR), deproteinized natural rubber (DPNR), synthetic polyisoprene (PI) and modified synthetic polyisoprene (PI-M). Composite electron spin resonance spectra with broad and narrow components appear in NR, DPNR and PI-M, above the glass transition temperature. The slow component is attributed to the spin probes in regions of higher density or gel phase, whereas the narrow component is identified with the nitroxides located in the sol phase. The intensity of the slow component depends both on the amount of gel phase and on the specific gel structure. The restricted spin probe motion above the glass transition is considered to be a measure of the participation of naturally occurring protein components or modifiers in the formation of gel and its structure. Several spin probes differing in size and shape are used in order to assess the free volume distribution.