Networks, polyurethane degree

The Flory-Rehner equation (2,13) was used to interpret the swelling of the polyurethane networks in pure dioxane in order to calculate, the molecular weight between crosslinks. Here, we set qQ= 1 and x the network-solvent interaction parameter, constant and assumed equal to 0.35 (3). Networks with degrees of swelling (q ) of 6.41, 11 and 21.1 yielded Mc values of 7,700,... 

Figure 1. The degree of swelling fqj of polyurethane networks in dioxane vapor over polystyrene solutions of various volume fractions ( s).

In the recent study made by us [63], the usual diol chain extender was replaced by a triol (TMP), producing crosslinked PU networks without phase segregation. The aim was to ensure high degrees of strain recoverability, to produce candidate thermally-triggered shape-memory polyurethanes. 

The formulations used in the manufacture of polyurethane elastomers are critical, as variations in the chemical composition of raw materials seriously affect properties. In particular, trace impurities can catalyze or inhibit the various reactions, changing network structures and hence final elastomer properties. For these reasons analytical tests to quantify the quality and reactivity of urethane intermediates have been developed and their use in urethane technology is essential. Additionally, characterization and identification of unknown polymers is frequently necessary. Finally, it is necessary to have procedures which characterize the structure and degree of crosslinking (where this applies) of polyurethane elastomers. 

V. V. Shilov, Yu. S. Lipatov, L. V. Karabanova, and L. M. Sergeeva, Phase Separation in the Interpenetrating Polymeric Networks on the Basis of Polyurethane and Polyurethane Acrylates, J. Polym. Sci. Polym. Chem. Ed. 17, 3083 (1979). Small-angle X-ray study. Thickness of transition layer, diffuseness of phase boundary, degree of miscibility determined. 

The effect of preliminaiy strain on the sorption of liquids of various chemical structure by segmented polyurethane and polyurethane ureas was investigated. It was shown that the swelling degree increases after strain as a result of partial destmction of domain structure and decrease in effective density of the physical network formed by hard domains. 

Unilink 4200 is a unique aromatic diamine originally developed by UOP as a chain extender for polyurethane elastomers. As a 2-functional diamine, Unilink 4200 builds linear polymer networks, allowing the polyurethane formulator to control the degree of cross-linking by the addition of higher functional polyols. 

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