ISSN:
0449-296X
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The stereochemical composition of the free radical alternating isobutene-maleic anhydride (IB/MA), isobutene-dimethyl fumarate (IB/DMF), and isobutene-dimethyl maleate (IB/DMM) copolymers was investigated by proton magnetic resonance. In contrast to the singlet gem-dimethyl resonance found in polyisobutene or in the alternating isobutene/acrylonitrile copolymer, the gem-dimethyl resonance of IB/MA, hydrolyzed IB/MA, and esterified IB/MA is a quadruplet with peaks of approximately equal intensity. The multiplicity of the spectra is consistent with the presence of equal amounts of threo-di-isotactic and threo-di-syndiotactic triads, disproving previous claims that such copolymers are predominantly threo-di-isotactic. The spectrum of the analogous IB/DMF indicates that the copolymer is composed entirely of erythro-di- isotactic and erythro-di-syndiotactic triads. This result is consistent with the exclusive trans opening of the dimethyl fumarate double bond and provides the first example for the stereospecific double bond opening of a noncyclic monomer in free radical polymerization. In contrast, the spectrum of IB/DMM shows that the dimethyl maleate double bond opens approximately 93% cis and 7% trans during copolymerization. Since the stereochemical composition of IB/DMF and IB/DMM is not the same, it is concluded that the radicals formed from dimethyl maleate and/or dimethyl fumarate do not equilibrate freely among all the possible configurations before isobutene addition.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1972.150100502
Permalink
