Why doesn’t PVF2 form a 31 helix?

The possibility of the existence of a 31 helix as a stable phase for poly(vinylidene fluoride) is investigated on the basis of intrachain and interchain interactions. The stable phase for PVF2 at low temperatures is well known to be the α phase, with a conformation of tgtg’, even though a calculation of the intrachain energy of a hypothetical helix leads to a value lower than that of the α phase. In this paper we discuss how the interchain energy acts to make the α phase the more stable conformation. Ingredients in this calculation include the compactness of chain packing and the results of imposing the condition of commensurability on the chain structure. [ABSTRACT FROM AUTHOR]