Effect of stereochemical sequence on the dynamics of atactic polypropylene melt

Abstract

Dynamic Monte Carlo (DMC) simulation was used to study the dynamics of a series of coarse-grained atactic polypropylene (aPP) model chains (C192H578) in the melt state at 473 K. Model chains with meso diads factions, P m , set at 0.25, 0.5, and 0.75 but with different meso and racemo diads sequences were studied. It was observed that aPP chains with an alternate meso and racemo diads sequence exhibited the highest mobility (or diffusivity) among all stereochemical sequences studied. Additionally, chains with long consecutive sequences of diads of the same type exhibited lower mobility than those with more random stereochemical sequences. The differences in the intramolecular and intermolecular interactions resulting from differences in diad sequences contributed to the observed differences in dynamics. In particular, intramolecular interactions play a more dominant role for aPP chains containing low fractions of meso diads or none at all (i.e., all racemo diads (P m =0.0) or syndiotactic chains). On the other hand, in the cases of P m values close to 1.0 (i.e., isotactic chains), intermolecular interactions play a more dominant role than the intramolecular interactions.