High-Resolution 13C NMR Investigations of Local Dynamics in Bulk Polymers at Temperatures Below and Above the Glass Transition Temperature

Abstract

In this chapter, we will first summarize the technical requirements for obtaining high-resolution solid-state 13C NMR spectra of bulk polymers. We will then review the bases of the determination and analysis, in terms of local motions, of the spectrum line shape, proton-carbon dipolar interactions, chemical-shift anisotropies, relaxation times and line widths. A large part of the chapter will be devoted to the description of studies that demonstrate the capability of NMR to investigate the local dynamics of bulk polymers at temperatures above and below the glass transition temperature, respectively. At temperatures below the glass transition temperature, the example of poly(cyclohexyl methacrylate) will illustrate the importance of line width measurements, whereas the chemical-shift parameters and 13C-1H dipolar interactions will be the relevant parameters for the study of aromatic copolyesters and epoxy resins. In the case of bulk polymers at temperatures well above the glass transition temperature, we will first examine the different expressions that have been proposed for the orientation autocorrelation function associated with the polymer local dynamics. Tests of these expressions will be carried out through the determination of the 13C spin-lattice relaxation times of a number of elastomers. Results thus obtained permit us to specify the main factors that control the local dynamics in bulk polymers at temperatures well above the glass-transition temperature. Then, NMR studies of compatible blends of polyvinylmethyl ether and polystyrene will show the possibility of investigating the relative influence of intramolecular interactions and intermolecular constraints on the local motions of a given blend component.