Molecular aspects of the rubber elasticity of poly(diethylene glycol terephthalate) networks

Abstract

for values of a > 5, the isotherms displayed a sharp increase or upturn in the reduced force [/*], which we attribute to maximum chain extensibility. In general, the networks exhibited a modulus significantly higher than would be expected on theoretical grounds. The theoretical analysis of the experimental results suggests that, for this particular system, there seems to be a high contribution to the elastic modulus from topological entanglements. According to this analysis, the molecular weight between entanglements lies in the vicinity of 2000. In order to get confirmatory evidence on the presence of entanglements in the fractions used in the preparation of the networks, dynamic viscoelastic measurements were carried out on un-cross-linked fractions lying in the range 4600-24 700. The time-temperature superposition principle was applied to the dynamic moduli to establish forms for the plateau and terminal responses, from which the relaxation spectra corresponding to these regions were determined. The presence of a minimum in the spectra separating the two sets of relaxation times corresponding to motions within entanglements and motions across entanglements loci suggests that relatively well-developed entanglements are already present in the low molecular weight fractions used in the preparation of the networks.

Synthesis, characterization, and rubber elasticity of end-linked poly(tetrahydrofuran) elastomer

“…On the basis of this realization, end-linked poly(tetrahydrofuran) networks were synthesized and characterized. The advantages of this system is multifold and as follows: (1) Prepolymer can be prepared by a well-defined cationic ring-opening living polymerization. (2) Difunctional initiator is readily available.…”