| Abstract
| - The miscibility of polypropylene (PP) melts in which the chains differ only in stereochemicalcomposition has been investigated by two different procedures. One approach used detailed localinformation from a Monte Carlo simulation of a single chain, and the other approach takes this informationfrom a rotational isomeric state model devised decades ago, for another purpose. The first approach usesPRISM theory to deduce the intermolecular packing in the polymer blend, while the second approachuses a Monte Carlo simulation of a coarse-grained representation of independent chains, expressed on ahigh-coordination lattice. Both approaches find a positive energy change upon mixing isotactic PP (iPP)and syndiotactic PP (sPP) chains in the melt. This conclusion is qualitatively consistent with observationspublished recently by Mülhaupt and co-workers. The size of the energy change on mixing is smaller inthe MC/PRISM approach than in the RIS/MC simulation, with the smaller energy change being in betteragreement with the experiment. The RIS/MC simulation finds no demixing for iPP and atacticpolypropylene (aPP) in the melt, consistent with several experimental observations in the literature.The demixing of the iPP/sPP blend may arise from attractive interactions in the sPP melt that aredisrupted when the sPP chains are diluted with aPP or iPP chains.
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