| Abstract
| - We have performed a molecular dynamics simulation study of atactic polystyrene (a-PS)and its dimer 2,4-diphenylpentane (DPP) using a previously derived quantum chemistry based explicitatom force field. The X-ray structure factor of a-PS obtained from simulations was found to be in goodagreement with experiment, reproducing the “amorphous” peak at around 1.4 Å-1 as well as the“polymerization peak” at around 0.75 Å-1 and its anomalous temperature dependence (increasing intensitywith increasing temperature). We found that the amorphous peak in a-PS arises primarily from phenyl−phenyl correlations, with important intramolecular and intermolecular contributions. While theintermolecular component was found to shift to lower q with increasing temperature, the intramolecularcomponent was found to be insensitive to temperature, resulting in a weak temperature dependence ofthe amorphous peak. Simulations revealed the presence of the polymerization peak in DPP, indicatingthat the designation “polymerization peak” for this feature is a misnomer. The polymerization peak inboth a-PS and DPP was found to be due primarily to intermolecular correlations of backbone atoms.This underlying correlation showed the expected decrease in intensity and shifting to lower q withincreasing temperature. The shifting to lower q of intermolecular phenyl−phenyl and phenyl−backbonecorrelations with increasing temperature was found to lead to the observed anomalous temperaturedependence of the polymerization peak.
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