Single crystals of guttapercha. Morphology, fold period, polymorphism and degradation behaviour

Abstract

AbstractGuttapercha (trans‐1.4‐polyisoprene) was crystallized from solution and its single crystal habit and chain folding characteristics were examined. The two polymorphic forms, known from previous studies, could now be assigned to two different single crystal habits by means of electron diffraction patterns, and conditions of their formation could be circumscribed. Similarly, the melting and annealing behaviour could be associated with the two forms and a transition between them observed at temperatures where the two phases can still coexist by present evidence. The fold length and its variations were also defined.Single crystals were exposed to the degrading effect of ozone, and changes in IR‐spectra and molecular weight distribution were followed. It was observed that, as expected, double bonds were severed; nevertheless a sizeable portion of them remained intact. At the same time the chain was broken down into a sharply defined fragment length which was identified as a trimer or tetramer of trans‐1.4‐polyisoprene with carboxylic and carbonylic termination. No appreciable selectivity as regards fold traverses analogous to the degradation products in polyethylene was observed. It is pointed out that appreciable accessibility of double bonds within the crystals, coupled with oxidation resistance of small oligomeric lengths, seems to be characteristic of chain folded crystals of unsaturated compounds with possible implications for studies on the crystal structure and on degradation behaviour in general.