Abstract
Gel-melting temperatures (Tmg) of ethylene-propylene random copolymer gels formed in n-hexane and n-octane were measured as a function of polymer concentration. The copolymers were heterogeneous in both composition and molecular weight. Tmg obeyed well the thermodynamic theory derived by Takahashi, in which gel→sol transition was treated as melting of crystalline junctions with fringed micelle-type morphology: Plots of 1/Tmg vs. lnV2N according to the theory were scaled on a common straight line when copolymers had similar propylene contents (PC), where V2 is the volume fraction of the copolymer in the gel and N is the weight-average degree of polymerization. Quantitative analysis of the theory, including measurements of dilute solution properties, led to the results that average size of crystalline junction ζ in number of ethylene units per crystalline sequence was ca. 11 for copolymers with PC=22 wt%, 9 for PC=26 and 27 wt%, and 5 for PC=49 wt%, and thus ζ decreased with increasing PC. The junction sizes ζ were reasonable order as compared with those estimated from X-ray diffractions.
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Okabe, M., Moteki, Y., Uranaka, H. et al. Study of Polyolefin Gel in Organic Solvents VIII. Size of Crystalline Junction and Structure of Ethylene-Propylene Random Copolymer Gel. Polym J 25, 955–967 (1993). https://doi.org/10.1295/polymj.25.955
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DOI: https://doi.org/10.1295/polymj.25.955