Studies on polyalkenamers. II. Degradation of polydodecenamer and polydecenamer single crystals

As part of an enquiry on the fold structure of crystals from unsaturated chains and on the relation between crystal morphology and degradation, single crystals of two polyalkenamers were subjected to oxidative attack by ozone, and to a lesser extent by nitric acid, and the resulting changes in the concentration of double bonds and the distribution of molecular lengths were followed. It was found that double bonds were attacked deep within the crystal without a clear distinction between the fold surface and the crystal interior in contrast to the analogous studies involving the severance of single bonds in polyethylene. Nevertheless, the attack does not follow a random pattern but leads to a crystalline dimeric residue which remains highly resistant in spite of containing double bonds. The implications of this unexpected finding, which include the possibility of a highly perfect crystalline subunit much smaller than involved in the much argued models of chain folded crystals, are discussed. It is reconfirmed that the occasional intrachain double bonds in polyethylene are largely shielded from ozone while in the lattice in contrast to the high accessibility of these bonds in the present polyalkenamers of closely similar crystal structure. In view of similar results on guttapercha7 it appears that the latter property may be a feature common to polymer crystals where the unsaturation is intrinsic to the molecule.