Swelling behaviour of rubber vulcanizates: 1. Real-time pulsed nuclear magnetic resonance measurements

Abstract

Swelling behaviour of acrylonitrile-butadiene copolymer rubber vulcanizates immersed in a nonprotonic solvent was studied by real-time pulsed nuclear magnetic resonance (n.m.r.) measurements. The temporal change of the proton spin-spin relaxation time, T 2, during the swelling process was obtained. The T 2 signal for the rubber vulcanizates was resolved into two exponentially decaying components (short T 2 and long T 2). The short T 2 component is assigned to the constrained regions in the rubber matrix, which may be mainly located around the crosslinks, and the long T 2 component to the regions lying outside the constraints. It was suggested that the decreased change of the fraction of the short T 2 component by swelling is closely connected with the enhanced molecular mobility of the network chains between the adjacent crosslinks through the diffusion of the solvent. The restricted swelling behaviour of the carbon black-filled rubber vulcanizates was interpreted mainly in terms of the constrained molecular motions of the network chains through the rubber-filler interactions and spatial effects of the filler particles. It becomes clear that the real-time pulsed n.m.r. measurements complement the results of the macroscopic swelling measurements for the rubber vulcanizates with more detailed information on the molecular interactions between the rubber and solvent molecules.