RUBBER ELASTICITY OF WELL-CHARACTERIZED POLYBUTADIENE NETWORKS

Polybutadiene networks in bulk and 50% solution were prepared by radiation-induced cross-linking of well-characterized primary chains. Equilibrium stress-strain behavior was measured in tension, and the initial (small deformation) modulus G0 as well as the individual Mooney-Rivlin parameters 2C1 and 2C2 were obtained. The initial modulus was interpreted as the sum of contributions from the chemical network structure Gc and the network topology Ge, the latter trapped in the structure when the network was formed. Within experimental error the maximum topological contribution, Gemax, obtained by the Langley analysis was equal to GN0, the stress relaxation plateau modulus prior to cross-linking: Gemax and GN0 are 1.18 and 1.16 MPa, respectively, for the undiluted polybutadiene, and 0.262 and 0.243 MPa for 50% solutions. The chemical network contribution in both cases was equal to values calculated from the phantom network theory with junction fluctuations suppressed. The value of 2C2 appears to be related in a simple way to the topological contribution. The value of 2C1 depends on both the chemical and topological contributions. © 1979, American Chemical Society. All rights reserved.