The microstructure of poly(divinyl acetal)s as determined by ¹³c NMR spectroscopy. ring stereochemistry and isomerization propagation

Divinyl formal, acetaldehyde divinyl acetal, and acetone divinyl acetal were polymerized freeradically, and the polymer structures were determined by detailed analyses of C NMR spectra. The carbon chemical shifts of various structures which might be formed by simple propagation, by cyclopolymerization, and by isomerization propagation were derived from those of a variety of model compounds and their combinations. All the polymers contained the cis-4, 5-disubstituted-1, 3-dioxolane ring as the predominant structural unit in the main chain (ca. 75%) and as the pendent group (ca. 25%). The latter structure was formed by hydrogen abstraction of the propagating methylenedioxolane radical from the neighboring methylene group. Similar hydrogen migration conceivably occurred also during the polymerization of diallylamines.