MELT CHAIN DIMENSIONS OF POLY(ETHYLENE-1-BUTENE) COPOLYMERS VIA SMALL-ANGLE NEUTRON-SCATTERING

The radii of gyration for a series of poly(ethylene-l-butene) copolyme rs of varying ethyl branch content were measured as a function of temp erature in the melt via small angle neutron scattering (SANS), and the ir temperature coefficients, d In C-infinity/dT = kappa, changed from negative to positive. The characteristic ratio C-infinity decreased wi th increasing ethyl branch frequency. When possible, these results wer e compared with those obtained from Theta solvents and from rotational isomeric (RIS) state theory. The SANS-based chain dimensions were sli ghtly larger than those obtained from Theta solvents. The values of ka ppa differed significantly from those extracted from Theta-solvent mea surements. Serious discrepancies with RIS-based calculations were obse rved.