Local Order and Induced Orientation in PDMS Model Networks, Studied by 2H NMR

Abstract

2H NMR experiments in a series of poly(dimethylsiloxane) end-linked networks are presented. The 2H NMR line shape in the relaxed state consists of a pseudo-solid contribution, with nonzero residual interactions, and a liquid contribution, with no residual interactions. The liquid part is attributed to dangling chains. The magnitude of residual interactions in the pseudo-solid part (elastic chains) is compared to the magnitude of the uniaxial order induced upon stretching uniaxially the networks. The induced order is measured by the splitting of the doublet which appears upon stretching. The splitting correlates also well with the polymer network volume fraction at swelling equilibrium. All these quantities are related to the properties of effectively elastic chains in the networks. The presence of dangling chains does not modify the interpretation given previously for the induced uniaxial order, in terms of a mean orientational field. The analysis which is presented allows one to estimate the strength of ...