Solution and solid state nuclear magnetic resonance spectroscopy of polyamides and crosslinked polyacrylates
The research presented in this dissertation focuses on the development of solution and solid state NMR techniques to characterize industrially relevant polymer systems. Chapters I and II discuss a new binary solvent (2,2,2-trifluoroethanol/chlorform) for polyamide solution 13 C NMR analysis that lead to well-resolved spectra and the appearance of several unidentified small peaks. In Chapter I, nylon 66 was investigated. Through the use of model compounds, the small peaks were identified as methylene carbons contained in (or in close proximity to) cis-amide conformers, acid and amine end-groups, and cyclic unimers. The amounts of these groups were quantified and molecular weights were determined based on relative solution 13 C NMR peak heights. In Chapter II, this analysis was expanded to cover a wide variety of polyamide homo- and copolymers. Several solution 13 C NMR peaks were identified that had chemical shift values unique to a particular polyamide. Thus using only solution 13 C NMR spectroscopy, nylon 6 could be identified and distinguished from other polyamide homopolymers (such as nylon 66, nylon 610 and nylon 12) and copolymers containing these monomer repeat units. In addition, the percentage copolymer composition, end-group content, cis-amide conformer content, residual monomer content and molecular weight could be determined using only solution 13 C NMR peak intensities. The result was the development of a routine solution NMR analysis method that can be used to quickly identify polyamide compositions. Chapters III and IV discuss research focused on developing an understanding of the interactions between nylon 6 chains and montmorillonite clay sheets, and how these interactions translate into physical property enhancements. Solution 13 C and solid state 15 N NMR evaluation of nylon 6/clay nanocomposites are discussed in Chapter III, and solid state 2 H NMR spectroscopic analysis of selectively deuterated nylon 6 and nylon 6/clay nanocomposite are discussed in Chapter IV. The result is a proposed model of how the nanocomposite components synergistically interact and what the effect these interactions have on polymer chain mobility and ultimate properties (Chapter IV). Chapter 5 describes direct observation of dimethacrylate crosslinker architectures in poly(methyl methacrylate) copolymers by solution 13 C NMR spectroscopy. Through the use of model compounds and isotopically labeled crosslinker, pendant methacrylate (mono-reacted crosslinker) and crosslinked (di-reacted crosslinker) architectures were observed in PMMA copolymers at less than 0.1 wt-% dimethacrylate incorporation. The result of this study is that a significant amount of dimethacrylate crosslinker is inefficiently incorporated into the copolymer.