Assignment of the Polymerization Peak in Polystyrene Melt*

Polymerization peak at around 0.75 Å^-1 in polystyrene (PS) melt was first reported by Katz in 1927, it is origin is still not clear. Here, by combined neutron total scattering, high concentration labelling and molecular dynamic simulation, we visualize the most-probable all-atom positions in polystyrene melt, and assign it to be the inter-chain backbone distance. In our experiments, both the neutron and x-ray total scattering profiles from 0.02 to 30 Å^-1 of PS-h8, PS-d8, PS-d5 and their mixtures (1:1 by molar) at different temperatures above their glass transition temperatures were measured. The low q scattering profiles in high concentration labelling mixtures are from the thermo fluctuations, while the intermediate and high q scattering profiles are assigned to the inter- and intra- chain atom-atom correlations.