Structural changes in polymer networks under deformation

The mechanism of changes in the molecular-mass distribution of interjunction chains in crosslinked poly(ether urethane) elastomers under deformation has been studied by the method of NMR spectroscopy. In the course of tensile drawing, the molecular-mass distribution changes nonmonotonically. The character of stress-induced changes shows that the breakdown of some bonds is accompanied by formation of new bonds and the development of network fragments with short chains. The strength and thermal stability of poly(ether urethane) elastomers are characterized by extremal dependences on the width of the molecular-mass distribution of interjunction chains. In the case of densely crosslinked and unannealed polyepoxides, mechanical impact (pressure and shear; grinding) is accompanied by changes in their supramolecular structure; in turn, these changes entail an increase in the thermal stability of the samples.