Nuclear Magnetic Resonance Study of Polyisobutylene CCl4 Solutions

摘要

The nuclear magnetic resonance relaxation times of CC14 solutions of polyisobutylene are measured by the spinecho method. The independent variables are the solution concentration and, in some cases, the temperature. Six polymer samples are used, with molecular weights covering the range 2 × 103 to 2 × 106. For each sample, a distinct break is found between dilute-solution behavior, where the relaxation times are independent of concentration, and concentrated-solution behavior, where the relaxation times decrease with increasing concentration In dilute solution, the two relaxation times are substantially equal, with a. value of about 75 millisec at 25°C, and show no systematic dependence on molecular weight (except that the spin-lattice relaxation time increases for very small molecular weight). The spin-spin relaxation time is inversely proportional to the viscosity of the solvent divided by the square of the absolute temperature. The relaxation times in dilute solution are attributed to the effects of local segmental reordering motions in the chain, with a correlation time of 10~9 sec at 25°C. The critical concentration below which the solution is "dilute" is consistent with statis­tical theories of molecular radius.