Abstract
A study has been made of the structures of the three dimensional network of a polyurethane based on trimethylolpropane phthalate cured with an aliphatic polyiscoyanate, biuret, at 20 ± 2°C. The degree of network formation has been assessed from the sorption of chloroform measured at 15 25 and 35°C and from the value of the equilibrium modulus of high elasticity. It is shown that the swelling of the polyurethane in chloroform is accompanied by restructuring within the system of physical bonds, which leads to the appearance of a number of regions of linearity on the linear sorption isotherm plotted with the coordinates of a modified Flory-Rehner equation. Sorption, thermomechanical and spectroscopic investigations show that a fairly open network, formed by chemical bonds ( M c=2500), is formed in the polyurethane. Physical nodes, diverse with respect to density ( M c of the order of 200 and 500), considerably raise the effective density of the network. Annealing these films or thermally ageing them in light lead to the physical nodes becoming more dense and to stabilization of the structure.
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