synopsisA method is proposed for use of the universal calibration curve, i.e., the product of molecular weight and intrinsic viscosity versw retention volume, in calculating the molecular weight distribution of a polymer from gel-permeation chromatography (GPC) when the Mark-Houwink relation of the polymer in the solvent used for the GPC is unknown. This is achieved by measuring the viscosity of each fraction with an automatic capillary tube viscometer. Application of this technique to poly(viny1 chloride) and poly(viny1 acetate) proved to be successful.
J . P o l~t n .Sci. A-2, 5,313 (1967).
Force‐temperature measurements at constant length and pressure are reported for amorphous, crosslinked networks of polyethylene and some ethylene‐propylene copolymers. The ratio of the energy contribution to the total tension, fe/f, calculated from these measurements and thermal expansion data, was found to depend strongly on the extension ratio as well as on the crosslink density. In current theory fe/fT is equal to the temperature coefficient of the unperturbed mean‐square end‐to‐end distance of the polymer chain in the network (d In (r02)/dT). The experimentally found nonconstancy of the fe/f makes it impossible to calculate a single value of d In (r20)/dT) for comparison with our a priori calculations of this quantity. These findings are at variance with previously published data of Flory, Ciferri, and Hoeve. Possibly, stress‐induced crystallization or, more generally, stress‐dependent intermolecular forces may play a role in thermoelas‐ticity studies under certain circumstances, in spite of the reversibility of the temperature cycles.
The energies of the various rotational states around the C-C bonds of a polyethylene chain are calculated with the aid of a selected function for the H-H interactions and the known functions for the distortion of bond angles and the torsional potential. The H-H function selected is the only one which reproduces the experimentally known energy difference of 800 cal./mole between the trans (t) and gauche (gL or gR) states of normal hutane and the value of 500 cal. /mole for the same difference in higher normal alkanes. The calculated energies are used to derive the reduced unperturbed mean square end-to-end distance /nl' and dln /dT are found to be 10 f 1 and-0.68.10-3, respectively. From the calculations it follows that the polyethylene chain can be considered as a kinked, irregularly helical structure. The irregularly helical parts consist of about 1 2 C-C bonds, which are either irregular combinations of gL and t states or of gR and t states. 2
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