Analysis of anomalous X‐ray diffraction effects of isotactic polystyrene gels and its implications for chain conformation and isomeric homogeneity

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Abstract
Oriented gels, obtained by high supercoolings of isotactic polystyrene solutions, exhibit unexpected “fiber‐type” x‐ray diffraction patterns. In particular a pronounced meridional reflection at a spacing of 0.51 nm, together with its successive orders, requires an extended, or nearly extended, chain conformation which appears irreconcilable with the stereochemistry of isotactic polystyrene. Furthermore, the value of 0.51 nm correlates directly with the axial projected repeat expected for two styrene monomer units. Two possible stereosequences merit atention: syndiotactic and syncephalic (head‐to‐head, tail‐to‐tail). In addition to the 0.51 nm meridional reflection, layer lines are observed with spacing 3.06 nm (6 × 0.51) which equate with 24 carbon–carbon bonds in the backbone. Cylindrically averaged Fourier transform calculations for the various models are compared with the observed x‐ray results and the best fit is obtained for a 24/11 helix of isolactic polystyrene with the syncephalic stereosequence. This conclusion, however, clashes with the 13CNMR evidence which indicates that the polymer is essentially isotactic. The implications of these novel results in relation to gel crystallization are discussed.