Polymer analysis by high‐resolution NMR, with applications to poly(vinylidene fluoride) and poly(vinyl fluoride)

Abstract

AbstractHigh‐resolution nuclear magnetic resonance (NMR) spectroscopy has been used for the past several years quite effectively in both the qualitative and quantitative determination of the molecular chain structures and compositions of various polymeric systems. Valuable structural information obtained from such NMR studies has included: (1) detailed stereo chemical configuration (both tacticities and stereoblock sizes) of the polymer chains, (2) copolymer compositions, (5) sequence distribution studies in copolymers, (4) determination of modes of monomer addition in both homopolymers and copolymers, and (5) extent of head‐to‐head structures. Currently, only H1 and F19 NMR techniques are being used in the elucidation of organic polymer structures, for reasons primarily of instrumental sensitivity but also involving general applicability. Examples of the utility of F19 and H1 NMR, as well as double‐resonance techniques, to determine chain structure and composition of fluorine‐containing polymers are presented in this paper. In particular, conclusive proof of a substantial amount (10–12%) of head‐to‐head structure and the detailed assignment of the F19 chemical shifts in poly(vinylidene fluoride) is presented. The existence of a very large amount (26–32%) of he ad‐to‐head structure in both experimental and commercial samples of poly(vinyl fluoride) is also shown (although the detailed assignment of the F19 NMR spectral peaks has not yet been completed); this indicates that about one monomer unit in every six or so is added “backwards” to the growing polymer chains during free‐radical homopolymerizations. Increase in the amount of head‐to‐head structure with increase in polymerization temperature is also observed for poly(vinyl fluoride).