2H NMR spin relaxation study of the molecular dynamics in poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK)

Abstract

Poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK) selectively 2H labelled in the ether–keto rings has been studied by 2H NMR T 1 relaxation time measurements. Partially relaxed 2H NMR lineshapes at 360 K indicate the predominant dynamic process as a phenyl ring π flip. Computer simulations based on the model of a delta function for a rigid, crystalline phase and a log–normal distribution of phenyl ring flip rates for the amorphous phase, show that fits to a combination of a simple and stretched exponential are possible. However, accurate fits to the experimental 2H saturation recovery curve based on exponential and stretched exponential functions could not be obtained over the full temperature range of 260–421 K. Constraining the fit to the trends seen in the computer simulations, allowed fits with only slightly increased errors suggesting that experimental error combined with the flexibility of the stretched exponential leads to the poor fits. The acquisition of improved experimental data is severely hampered by the long crystalline phase T 1. An estimate of the fast flipping fraction was made on the basis of the intensity after 100 ms recovery in the 2H saturation recovery curve. From the increase in the fast flipping fraction with temperature, an energy of free volume formation of 10±2 kJ mol −1 can be estimated. Evidence was found for fraction of the rings in the amorphous phase not undergoing π flips at the T g.