Interfacial effects on the NMR of composite polymers

Abstract

Several NMR experiments can provide estimates of the scale of spatial inhomogeneity in solid materials in the range of nanometers to microns. The effects underlying these experiments their interpretation, and models used in their interpretation are discussed and illustrated with applications to polymers. Examples chosen from the literature include semicrystalline polymers (polyethylene, polyvinylidene fluoride, polychlorotrifluoroethylene), filled elastomers (carbon‐filled butadiene), copolymers (styrene: butadiene, dimethylsiloxane: bisphenol‐A polycarbonate, polyurethane) and blends (polymethylmethacrylate‐polystyreneacrylonitrile, polyvinylidene fluoride‐polymethylmethacrylate). Comparison of examples directs attention to the similarity in anisotropic motional behavior of highly constrained interfacial material in semicrystalline and filled polymers. While no one experiment is applicable to all dimensions, or all systems, NMR has proven especially useful for dimensions in the range of tens of nanometers, where other techniques are often less revealing.

Use of carbon–carbon nuclear spin diffusion for the study of the miscibility of polymer blends

“…We observed small but significant differences in the time dependence of the signal intensities observed under different initial conditions (see Figs. [13][14][15][16]. Special precautions have been taken to minimize possible temperature drifts, by use of an improved air-cooling system for the probe and longer delay times between successive acquisitions.…”

NMR Studies of Organic Thin films

“…Most elastomers used for applications from balloons to tires are made from 1.4 nm of which was tightly-bound material (75,87).…”

Molecular mobility in rubbery composites: Effect of filler particle size

“…In an effort to determine an upper limit on the width of the distribution of T2s in our composites, we attempted to reproduce the observed decays by modifying eq. (1) to have two or three fast components of differing relaxation times, but with a common E = 2.0, the (Gaussian) maximum exponent reportedz7 in rubber-based composites. We find that our decays cannot be convincingly reproduced by a superposition of components with a significant range of decay times; they cannot be approximated at all by single or multiple exponential decays.…”

“…The values of fs obtained by fitting eq. (1) to the spin-spin decay data are shown as function of curative content in the form of a reactive end-group (nominal NCO-to-OH) ratio, for the six composite series as well as the (unfilled) gum stock. The gel fraction has a maximum near an effective stoichiometry, and falls off on both sides, but more steeply toward lower NCO/ OH especially in the composites.…”