Two Types of Topological Constraints in Polymer Networks

It is proposed to distinguish two types of topological constraints in the nonphantom network: one corresponds to entanglements between different subchains in the network, and the other can be described as self-entanglement of a subchain with itself. The number of effective entanglements of the intersubchain type is found to be an increasing function of the network swelling ratio α. This explains the experimentally observed nonmonotonic dependence of the elastic modulus of the network on α. A new “preparation parameter”, [formula omitted], is introduced which characterizes the degree of entanglement between subchains of the network and which depends on network preparation. The relative importance of constraints of intra- and intersubchain types depends on the value of Ƥ. Intrasubchain constraints prevail in a network with small [formula omitted] in the collapsed regime and, in the strongly collapsed regime, lead to a crumpled-globule structure of the network.