MOLECULAR-DYNAMICS SIMULATION OF ATACTIC POLYSTYRENE .2. COMPARISON WITH NEUTRON-SCATTERING DATA

Four polystyrene samples, some selectively deuterated, were synthesized by anionic polymerization for neutron scattering measurement. The four are a predeuterated polystyrene, a polystyrene with its phenyl group deuterated, one with its aliphatic backbone deuterated, and a hydrogenous polystyrene. Neutron scattering measurement was performed by a method employing a spin polarization analysis, which allows unambiguous separation of coherent from incoherent scattering. The coherent scattering differential cross section determined in absolute units was compared with calculated curves based on the result of molecular dynamics simulation of atactic polystyrene. The simulation was performed with a united atom model and an all atom model, in both of which the bond lengths were held fixed and the phenyl group was constrained to a rigid, planar hexagon. The curves calculated from the united atom model were seen to agree fairly well with the experimental data within the experimental uncertainties due to counting statistics. The all atom model, however, gave a less satisfactory agreement-a result, which is similar to the one presented in a previous paper where X-ray scattering data in the literature were compared with simulation results. From the simulation, six different pair distribution functions giving the correlations among carbons, backbone hydrogens, and phenyl hydrogens were calculated, and from them the corresponding partial structure factors were evaluated to see the contributions which each type of pair makes to the overall neutron scattering curves.