Determination of the molecular weight between cross‐links of elastomeric stocks by tensile retraction measurements. II. Polyurethanes

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Abstract
Tensile retraction measurements of Mc were made on a variety of polyurethanes or polyurethane‐ureas. These samples were prepared using a number of prepolymer MW and functionalities. In addition, the stoichiometry of the cure was allowed to range widely. In all cases, excellent linear correlation coefficients were obtained between the Mc and the Amax of the test. The slope and Mr (the value of Mc extrapolated to Amax = 1) determined from this was used to characterize the polymer. These data allowed the determination of χ for each of the different systems such that comparable values of Mc could be measured by swelling. Identical formulations cured at different temperatures were shown to have measurable differences in Mc, slope, and percentage set. These variations appear to relate to the perfection of the network and morphology of the hard domains.