Autooxidative degradation of high molecular-weight poly(phenylacetylene) (PPhA) in solid state and in solution was studied using the size exclusion chromatography (SEC) and UV, IR, and EPR spectrometry. No degradation was observed on PPhA stored in vacuum, whereas the polymer exposed to air was found to degrade without any induction period. No evidence of a cross-linking of oxidized PPhA was observed. The degradation of PPhA was found to be: (i) practically non-influenced by an ambient, diffuse day-light; (ii) of the random type (i.e. each main-chain bond of PPhA has the same probability of being ruptured); and (iii) fast enough to influence the results of SEC measurements.

Abstract3‐Ethynylthiophene (3ETh) was polymerized with Rh(I) complexes: [Rh(cod)acac], [Rh(nbd)acac], [Rh(cod)Cl]2, and [Rh(nbd)Cl]2 (cod is η2:η2‐cycloocta‐1,5‐diene and nbd η2:η2‐norborna‐2,5‐diene), used as homogeneous catalysts and with the last two complexes anchored on mesoporous polybenzimidazole (PBI) beads: [Rh(cod)Cl]2/PBI and [Rh(nbd)Cl]2/PBI used as heterogeneous catalysts. All tested catalyst systems give high‐cis poly(3ETh). In situ NMR study of homogeneous polymerizations induced with [Rh(cod)acac] and [Rh(nbd)acac] complexes has revealed: (i) a transformation of acac ligands into free acetylacetone (Hacac) occurring since the early stage of polymerization, which suggests that this reaction is part of the initiation, (ii) that the initiation is rather slow in both of these polymerization systems, and (iii) a release of cod ligand from [Rh(cod)acac] complex but no release of nbd ligand from [Rh(nbd)acac] complex during the polymerization. The stability of diene ligand binding to Rh‐atom in [Rh(diene)acac] catalysts remarkably affects only the molecular weight but not the yield of poly(3ETh). The heterogeneous catalyst systems also provide high‐cis poly(3ETh), which is of very low contamination with catalyst residues since a leaching of anchored Rh complexes is negligible. The course of heterogeneous polymerizations is somewhat affected by limitations arising from the diffusion of monomer inside catalyst beads. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2776–2787, 2008

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Dilute solution characteristics of atactic (ca. 30% trans) poly(phenylacetylene), PPA, were determined by using the SEC/MALS technique in order to obtain a deeper insight into discrepancy between presumed rigidity of conjugated polyvinylene molecules and their random-coil behavior in solutions resulting from earlier viscometry measurements. PPA was found to exhibit the molecular-weight dependence of the radius of gyration in tetrahydrofuran solution similar to that of atactic polystyrene (saturated analogue of PPA); also unperturbed dimensions of these polymers are almost equal. This rather surprising observation is explained as a consequence of the increased π-π attraction between highly polarizable PPA segments with well-delocalized π-electrons, which compensates the effect of stiffening of these segments due to conjugation. Possible influence of chain branching is also discussed.