Microstructure characterization of acetylenic polymers by Curie-point pyrolysis/capillary gas chromatography/mass spectrometry

Abstract

The degradation of homo- and copolymers of 1-hexyne and phenylacetylene synthesized with a Ziegler-Natta initiating system and a metathesis catalyst have been investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in order to describe the monomer arrangement in the macromolecular chains. The experiments were performed at 500°C using a Curie-point pyrolyzer and the products were separated by means of a capillary column GC. The most characteristic pyrolysis products were identified by Py-GC/MS coupling and by comparison with the retention data of anticipated degradation compounds. After discussion of the respective thermal degradation behaviour of poly(1-hexyne), polyphenylacetylene, blends of these polymers and copolymers of various compositions, the chain microstructures were studied through the quantitative treatment of the characteristic homogeneous trimers and hybrid trimers of the 1,2,4- and 1,3,5-trisubstituted benzene type formed during the pyrolysis. The relative yields of 1,2,4- and 1,3,5-cyclotrimers were quantitatively related to the corresponding head-to-head (or tail-to-tail) and head-to-tail monomer linkages in the homo- and copolymer chains. Furthermore, by applying the ‘both-side boundary effect’ theory to the molar amounts of the various cyclotrimers which depend both upon copolymer compositions and pentad sequence distributions, the relative values of the trimer formation probability constants were calculated. Then, the run number of each pyrolyzed sample was evaluated using these parameters. The analytical data thus obtained are in good agreement with those predicted by the usual theory of copolymerization.