Elastic properties of model polymer networks

Abstract

Polymer networks prepared in such a way as to have known structural characteristics are of fundamental importance in the establishment of reliable structure—property relationships for elastomeric materials. The synthesis and utilization of such “model” elastomers is illustrated using unfilled polydimethylsiloxane (PDMS) networks prepared by two highly selective techniques: (i) the end-linking of hydroxyl—terminated PDMS chains of known molecular weight and molecular weight distribution, by means of either a tetrafunctional or trifunctional silicate, and (ii) the end—linking of vinyl—terminated chains and cross-linking of vinyl—substituted chains using a number of silanes designed to yield a wide range in junction functionality. The series of model PDMS networks thus obtained were investigated with regard to their stress—strain isotherms in elongation up to their rupture points, and their equilibrium swelling in a thermodynamically good solvent. The results provide important information on the dependence of elastic properties on the structural characteristics of the networks, including (i) the average molecular weight of the network chains, (ii) the network chain length distribution, (iii) the limited extensibility of the network chains, (iv) the functionality of the network junctions, and (v) the presence of dangling-chain irregularities. © 1981 IUPAC.