Effect of dilution during network formation on the sol fraction and elasticity of polyurethane networks

Abstract

The effect of dilution at network formation (polymer volume fraction do) = 1 -0,4) on the fraction and equilibrium photoelastic behaviour of polyurethane networks was investigated. The networks were prepared from poly(oxypropy1ene)triol and 4,4'-methylenedi(phenyl isocyanate) with various mole ratios of reactive groups 1 < rH = [OH]/[NCO] < I ,5. From a comparison between the experiments and the theory of branching processes we find that: a) with both increasing ratio rH and increasing dilution the fraction of bonds lost in elastically inactive cycles increases from 0,02 to 0,06; b) the experimental reduced equilibrium moduli G, of the predominant majority of samples are higher than those theoretically predicted by the Flory junction-fluctuation theory for the front factor A = 1. Also the decrease of G, with dilution (expressed as volume fraction of diluent during network formation do)) is very steep, thus supporting the contribution of permanent interchain constraints to the overall G, value.

Static and Dynamic Mechanical Behavior of Electron Beam‐Cured Monomer and Monomer/Liquid Crystal Systems

“…Topological defects such as loops and pendant chains are a source of decrease in the elastic modulus and the mechanical strength of the material. [10][11][12][13][14][15] Figure 5a and 5b compare the stress-strain dependencies for several films of TPGDA/E7 and GPTA/E7, respectively. The data in these figures are taken at room temperature (20 8C) on samples obtained from the relatively high EB dose of 105 kGy.…”

Polyfunctional Cross-Linking of Existing Polymer Chains

“…It was found that the chain ends and trapped entanglements affect the value of equilibrium modulus, 1-3 whereas the shape of viscoelastic functions in dependence on frequency and temperature in the main transition region also depends on the length of the DCs. [4][5][6][7] The strong increase in the width of the retardation spectrum with increasing number and length of dangling chains was observed for polyurethane 5,6 as well as epoxide 7 networks. It was also established that the decisive influence on the spectrum width is exerted by the increasing molecular weight of DCs.…”

Equilibrium Phase Diagrams of Interpenetrating Polymer Networks and Liquid Crystals

“…Polymer gels have attracted considerable attention from the point of view of various physical and chemical properties 1–5. For example, hydroelectrolyte gels show a dramatic change in volume in response to change in solvent composition, pH, ionic strength, and temperature.…”