A comment on “crystallinity” in poly (olefin sulphones)

It is suggested that seemingly crystalline structures which have been observed in films of poly(olefin sulphones) cast from solution in liquid SO₂ are voids that replicate (in three dimensions) dendritic crystals which originally formed as a consequence of the condensation of moisture on the cold rapidly-evaporating solution and which subsequently evanesced by sublimation or melting and evaporation. This has been shown directly in the case of poly(butene-l-sulphone) and also simulated in an indisputably non-crystallizable polymer (atactic poly(methyl methacrylate)). At least two crystalline species are produced by condensing moisture under these conditions, one with hexagonal symmetry (presumably ice I_h) and one with cubic symmetry (apparently a known clathrate hydrate of SO₂). It is further suggested that similar “crystalline” structures observed by Brady and O'Donnell 1] in films of poly(3-methyl-1-butene sulphone) cast from SO₂ rich mixtures, and assumed by them to be a crystalline phase of the polymer, have a similar origin. This assumption formed the basis of their explanation of a thermodynamic anomaly in the formation of insoluble poly(olefin sulphones), an explanation which is now open to serious question.