Problems of structural characterization of polymer networks

Problems of the characterization of network structure by investigating the network formation and its response to mechanical stress have been analyzed. Attention has been devoted to the effect of reactivity of functional groups and cyclization on the formation of network structure and to problems of obtaining the equilibrium modulus and its relation to the concentration of elastically active network chains (EANCs). It has been demonstrated that a theoretical description of network formation must be based on reliable information on the rules of joining of functional groups and on their relative reactivity; the tree‐like approximation offers a number of structural parameters of the sol and gel including, e.g, chemical clustering of units of a certain type. The main obstacles to reaching the equilibrium modulus are long relaxation, times of lightly crosslinked networks and the occurrence of secondary relaxations. In correlating the equilibrium modulus and the concentration of EANCs, it is necessary to find conditions under which the Mooney‐Rivlin constant C 2 can be neglected and to carry out the required corrections of the modulus, if experimental conditions differ from those of network formation.