Molecular dimensions in the delta and gamma phases of syndiotactic polystyrene, using small angle neutron scattering

The delta phase of syndiotactic polystyrene/ethylbenzene has previously been shown to involve a sheet-like arrangement of crystal stems, with superfolding at higher molecular weights. SANS measurements have been made using tilted samples in order to separate in-plane and out-of-plane radii of gyration. Use of intensities from the whole area of the detector allows the determination of these quantities with good precision. Comparison between the out-of-plane radius and the long spacing determined from small angle X-ray measurements shows close agreement for the lower molecular weight ((M) over bar(w), = 42 700) in both delta and gamma phases, while R-z is a factor of 2 larger for the higher molecular weight ((M) over bar(w) = 124500). This indicates that each molecule occupies a single lamella at the lower molecular weight and, on average, two lamellae at the higher one, in both delta and gamma phases. This provides clear evidence of tie molecules at the higher molecular weight, and also implies that the delta to gamma phase transition only involves a reorganisation of chain segments within those lamellae which originally contained the molecule. (C) 1999 Elsevier Science Ltd. All rights reserved.