Chain conformation in molten and solid polystyrene and polyethylene by low-angle neutron scattering

Abstract

Measurements of radius of gyration, ^½and persistence length of polymer molecules in bulk atactic polystyrene have been made by low-angle neutron scattering (LANS) from dilute solutions of protonated polystyrene (PSH) in a deuterated polystyrene (PSD) matrix. The measured values of ^½ lie close to those measured in θ solvents and have a molecular weight dependence of M^½ + ε = 0.04 ± 0.04. The molecular configuration agrees closely with that of a random coil with a persistence length ∼ 10 Å. These measurements support the model of an unperturbed Gaussian coil in which the distribution of chain segments is random above ∼ 20 Å. Measurements of ^½ throughout the glass transition region indicate that the overall conformation of the polymer chain does not change on heating through this region. Chain conformation in molten polyethylene has been measured by (LANS) from dilute solutions of (PED) molecules in a protonated polyethylene (PEH) matrix, and PEH molecules in a PED matrix. The measured values of radii of gyration can be expressed as^½ = k = M^½ _w with k = 0.63 ±^w 0.15, compared to a value of k = 0.45 ± w 0.03. in θ solvent. Thus chain dimensions in the melt appear to again be close to those found in θ solvents. The measurements revealed a tendency to separation (clustering) between PEH and PED molecules, though this tendency is small in the liquid state and does not significantly affect the above result. However, the tendency to clustering is much greater in the solid state and special care is necessary to avoid it. The implications of these findings on recent IR studies of chain reentry in lamallae are discussed.