Effect of tacticity on coil dimensions and thermodynamic properties of polypropylene

Todd D. Jones, Kimberly A. Chaffin, Frank S. Bates, B. K. Annis, E. W. Hagaman, Man Ho Kim, George D. Wignall, W. Fan, R. Waymouth

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Small-angle neutron scattering (SANS) has been used to measure the chain dimensions of syndiotactic polypropylene (s-PP) in the melt, using mixtures of 1H- and 2D-labeled molecules. This leads to a segment length 7.6 Å normalized to a four-carbon repeat unit, which is in excellent agreement with a prediction based on a correlation of chain conformation and the plateau modulus obtained from theology. The s-PP segment length is substantially higher than the values of 6.2 Å previously obtained for isotactic polypropylene (i-PP) in the melt and 5.6 Å in a low-molecular-weight "polymeric solvent". We have also studied its effect on the thermodynamics of polyolefin blends by investigating the miscibility of s-PP with a range of atactic poly(ethylene/ethylethyelene) (PEEx) random copolymers, with x% ethylethylene, and comparing this with i-PP. The miscibility "window" of i-PP with PEEx ranges from x = 63-96% ethylethylene, while that of s-PP is shifted to x = 53-73%, in qualitative agreement with the concept that conformational symmetry matching favors miscibility. We have also performed a complementary measurement of the melt coil dimensions of s-PP, using a low-molecular-weight PEEx "polymeric solvent" similar to that previously employed for i-PP. A fit of the s-PP/PEE71 blend scattering yielded a segment length of 8.1 Å, supporting the previous finding that the coil dimensions of s-PP are substantially higher than i-PP. These results emphasize the important influence of tacticity on the chain dimensions and thermodynamic properties in polyolefin systems.

Original languageEnglish (US)
Pages (from-to)5061-5068
Number of pages8
Issue number13
StatePublished - Jun 18 2002

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