Crosslinks to Properties

It will thus be obvious that both covalent and polar crosslinks contribute to the crosslink network and hence modulus of polyurethane elastomers. The dependence of this modulus or temperature can be divided into contributions from a covalently linked network conforming to the statistical theory of rubber elasticity, and contributions from secondary crosslinks which are assumed to have a temperature dependence governed by the Arrhenius law in which the modulus of elasticity is represented by the equation  

CONTRIBUTIONS OF PRIMARY AND SECONDARY CROSSLINKS TO THE MODULUS OF DIAMINE CHAIN-EXTENDED POLYESTER URETHANE ELASTOMERS  

Based on poly(ethylene-plus propylene adipate) (70 30)/MDI/MOCA, TO 20 0 60-0-90. 

The contribution which the different types of polar groups make to the properties of polyurethane elastomers depends in part upon their ability to enter into strong hydrogen-bonded associations. The substituted urea linkage, formed by the reaction of an isocyanate with an amine, is regarded as exceptional in its contribution to the physical properties, and it is therefore a preferred component in many bulk elastomers where the structural irregularity introduced by the use of a non-symmetrical diisocyanate or polyol is compensated by the strong urea interactions. 

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