Degradation of Substituted Polyacetylenes and Effect of This Process on SEC Analysis of These Polymers

Abstract

Survey of advances in the fields of: (i) spontaneous autoxidative degradation of substituted polyacetylenes, and (ii) effect of this process on SEC analyses of these polymers, involving already published and new original results is presented. The degradation is shown to be, essentially, of the random type but accompanied by the enhanced low-MW species elimination in case of high-cis polymers. These species are suggested to be formed in the reactive relaxation of excited ends of primary fragments resulting from the random oxidative cleavage of macromolecules. The degradation proceeds even in SEC columns and distorts results of the polymer SEC analysis. Theoretical treatment and computer simulation of such analyses provided information on the results' distortion extent and showed that systematically biased MW averages provide plausible degradation rate constants.Size partitioning of macromolecules in SEC columns is more or less perturbed by various hydrodynamic and thermodynamic effects that do not alter a constitution of analyzed macromolecules (1-3). Only in case of very long macromolecules, typically with MW above 5-10 6 , the degradation induced by hydrodynamic shear forces can occur in SEC columns (4,5). This process has been reported for various high-MW polymers like poly(styrene), polyethylene, poly(methyl methacrylate), poly(isoprene), poly(oxyethylene) and poly(isobutylene) (4-15) so that it is well established and known,.nowadays. On the other hand, little is yet known on the effect of chemically induced degradation in the polymer SEC analysis that was recently demonstrated in the case of poly(phenylacetylene) (16) which undergoes rather fast oxidative degradation in soluSupported by the Ministry of Education of the Czech Republic, Project VS 97103.

Electronic processes in end-functionalized oligomeric poly(diphenylvinylene)s

“…It is notable that, e.g., carotenes, retinals, zeaxanthines and related compounds, which, from the structural viewpoint, are oligomers of substituted acetylenes (oligovinylenes), effectively function as molecular wires in the living matter (photosynthesis systems, vision) for hundreds millions of years. Although high-molecular-weight polyacetylenes show many unique properties [4,5], unfortunately, they are mostly unstable in air [6][7][8][9][10][11][12][13], undergoing autoxidative degradation, which makes their practical applications difficult or even impossible. Nevertheless, polymers of disubstituted acetylenes are practically stable in air [14,15], which, evidently, is due to the absence of main chain vinylic hydrogen and effective protection of their conjugated main chains by substituents.…”