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Molecular Origin of Demixing, Prior to Crystallization, of Atactic polypropylene/isotactic Polypropylene Blends Upon Cooling From the Melt

Molecular Origin of Demixing, Prior to Crystallization, of Atactic polypropylene/isotactic Polypropylene Blends Upon Cooling From the Melt

Phillip Choi, Wayne L Mattice

J Chem Phys. 2004 Nov 1;121(17):8647-51.

PMID: 15511192

Abstract:

An amorphous 50/50 atactic polypropylene (aPP)/isotactic polypropylene (iPP) mixture at 125 degrees C was simulated using a second nearest neighbor diamond lattice and a three states rotational isometric state model. The result suggests that at the liquidlike density that corresponds to the atmospheric pressure, aPP prefers to interact with other aPP chains rather than with iPP chains. The result is consistent with the inference of Keith and Padden [J. Appl. Phys. 35, 1286 (1964)] that aPP and iPP will tend to separate from one another in their melt at 125 degrees C, before the onset of crystallization of iPP. The tendency for immiscibility of the amorphous aPP/iPP blend is likely attributed to the presence of short syndiotactic sequences in the aPP chains adopting all-trans conformations. The attractive intermolecular interaction of pairs of such subchains at 125 degrees C promotes the separation of aPP from iPP. This interaction is weakened at higher temperature, where aPP and iPP become miscible. The result also shows that miscibility of the blend increases with increasing pressure. However, the origin of the pressure effect is not clear.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP25085534	Polypropylene, isotactic		25085-53-4	Price

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