On the Stereoregularity of Vinyl Polymer Chains

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Abstract
We explore quantitatively the kind and extent of information concerning the distribution of configurational sequences in vinyl (and related) polymer chains obtainable from data such as presently available high-resolution NMR spectroscopy measurements. After finding the number of observationally distinguishable types of sequences, containing n monomer units [n(ads)], we obtain the necessary consistency relations which must hold between the observed proportions of n(ads), explicitly for all n≤5. Geometrically, the possible regions accessible to the n(ad) proportions form certain simplexes in a space of D(n) dimensions. The extreme points always correspond to repeating polymers. The computed dimensionality number D(n) plays a central role in fixing the number of free parameters of the polymer propagation model determinable by an n(ad) analysis. We discuss in some detail certain Markovian and the non-Markovian Coleman—Fox propagation model in relation to n(ad) analysis. We introduce the concept of a completely reversible polymerization mechanism. We include in our discussion chains of alternating tacticity such as can be found on polymerizing α, β disubstituted monomers. We present a number of actual examples based on available NMR spectra of certain polymer samples which illustrate how our formalism is useful in (1) checking the consistency of peak and (2) checking the consistency of peak proportion assignment, (3) predicting lower-order n(ad) frequencies (unobtainable because of spectral complexity) from higher-order n(ad) frequencies, (4) ruling out certain propagation mechanisms, etc.