A Study on the Relationships between Network Structure and Mechanical Properties of Interpenetrating Polymer Networks-Part I: A New Molecular Theory of Viscoelasticity for Thermoplastic Polyurethane Elastomers

Abstract

A new molecular theory of nonlinear viscoelasticity for crystallizable thermoplastic polyurethane elastomers (CTPUE) possessing the capability of characterizing the mechanical properties both at small and at large deformations is presented and verified by experimental data. Based on the proposed structure for CTPUE and the mechanism of large deformation, the probability distribution functions of the end-to-end vectors for five kinds of constituent chains were calculated. Also, the free energy of deformation for the microstructures including three kinds of networks and induced crystallites was calculated. The theory successfully related the viscoelastic behaviors to molecular constitution by three important network parameters (C,₁₀₀, C₀₂₀ and C₂₀₀). The constitutive equations for various types of deformation were obtained and the relation of modulus to relaxation time was derived. It provides a theoretical foundation for studying the relations between the structure of networks and the mechanical properties of CTPUE at large deformations.

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