Nuclear magnetic resonance in polyisobutylene

Abstract

The proton resonance spin-lattice relaxation time (T1) and the spin-spin relaxation time (T2) have been measured for polyisobutylene over the temperature range 20C to 210C. There is a minimum in T1 at 50C and two values of T2 above 170C.The results are interpreted (together with previous results giving second moment values over the temperature range 50C to +50C) by correlating them with data on dielectric and mechanical losses and on flow viscosity. It is found that the results can only be consistently interpreted by introducing two main molecular motions differing in frequency by a factor of some 109, each involving a distribution of relaxation frequencies. The analysis shows the importance of distributions of relaxation times for nuclear resonance and the uncertainty in the meaning of apparent activation energies deduced from the variation of line width, TZ or T1 with temperature.The nuclear resonance measurements reinforce the suggestion from the mechanical, dielectric and viscosity data that one correlation-frequency band is associated with molecular chain motion, probably with a small number of links of the chain as the controlling mechanism. The other slower one is probably associated with the motion of longer sections.