Proton Magnetic Resonance Studies on Natural Rubber. II. Line Shape and <i>T</i>1 Measurements

Abstract

Proton magnetic resonance absorption measurements have been made on samples of uncured Hevea, balata, and Coral rubber as well as on vulcanized samples with up to 9% combined sulfur. The motions of the chain segments were studied by observing line shapes and spin-lattice relaxation times at temperatures between —190 and 150°C. Several types of data show different molecular mobilities for vulcanized samples with a given combined sulfur but prepared by curing mixes with different fractions of raw sulfur for different times. Line width studies of the uncured Hevea sample as a function of thermal history indicate that the molecular mobility decreases with increasing crystallinity. Chemical shifts were resolved in high resolution studies of solutions of uncured Hevea, balata, and Coral rubber. The T1 measurements, including observations at 20 and 28 Mc/sec on uncured Hevea and balata, exhibit systematic deviations from the BPP theory. The significance of the deviations is discussed.