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The radii of gyration for a series of poly(ethylene−1-butene) copolymers of varying ethyl branch content were measured as a function of temperature in the melt via small angle neutron scattering (SANS), and their temperature coefficients, d ln C ∞ /d T = κ, changed from negative to positive. The characteristic ratio C ∞ decreased with increasing ethyl branch frequency. When possible, these results were compared with those obtained from ϑ solvents and from rotational isomeric (RIS) state theory. The SANS-based chain dimensions were slightly larger than those obtained from ϑ solvents. The values of κ differed significantly from those extracted from ϑ-solvent measurements. Serious discrepancies with RIS-based calculations were observed.
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Fetters et al. (1997) studied this question.
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