Characterization of the Structures of Diene Polymers by NMR

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Abstract
Nuclear magnetic resonance spectroscopy (NMR) has become a very powerful tool for characterizing the structures of elastomers, providing information about their compositions and the arrangements of their constituents along their chains. Elastomers derived from diene monomers by homopolymerization or copolymerization can be very difficult to characterize because of the large number of structural features that may be present. Dienes can be incorporated as 1,2, 3,4, cis-1,4, or trans-1,4 units, and also as cis-4,1 or trans-4,1 units in some cases, for example. This leads to the possibility of head-head and tail-tail linkages as well as head-tail linkages and to the possibility of several stereochemical arrangements existing between pairs of 1,2-units. In spite of this difficulty, quantitative information about the structural characteristics of polymers derived from dienes can be obtained from their NMR spectra, and this information has been very useful in studies on polymerization mechanisms and elastomer properties. In some cases, it is possible to study the structures of growing chain ends by NMR spectroscopy. This, of course, provides valuable information about the polymerization mechanism. Nuclear magnetic resonance can be used to monitor chemical changes occurring in elastomers, such as oxidation or vulcanization. It can also provide information about the dynamic characteristics of elastomeric chains. Reviews on the characterization of elastomer structure by nuclear magnetic resonance are available, but developments in the characterization of polymers derived from dienes have occurred so rapidly that it is appropriate to review this specific topic at this time.

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