Chapter 13 Poly(imide)s

Abstract

NMR spectroscopy, and in particular solid-state nuclear magnetic resonance (NMR), has an important role to play in the determination of structure, conformation, morphology, and molecular motion in poly(imide) materials. This chapter discusses the various classes of poly(imide)s and reviews the current literature on NMR of these materials. Infra red (IR) spectroscopy has often been used to study the conversion of amic acids to imides. Despite the popularity of this technique, important questions have been raised concerning the quantitative aspects of the results, especially at high conversion. NMR spectroscopy, in particular solution-state NMR, has the advantage of greater chemical information, and when care is taken, provides quantitative measurements of the extent of conversion of amic acid to imide. For many complex poly(imide) mixtures, the NMR spectra are severely overlapped, due to the structural similarity of many of the monomer repeat units and also the presence of a range of conformations frozen-in in the solid state. The use of isotopic enrichment of selected sites, with 15 N or 13 C nuclei, can alleviate this problem. However, such a course of action is tedious and expensive. An alternate method for improving resolution in the cross polarization and magic angle spinning (CPMAS) spectra is to measure the spectra above the glass-transition temperature of the materials, thus allowing averaging of conformations frozen in the glassy state.