| Abstract: | Stress–strain behavior in extension and the swelling of polymer networks with different lenghts of crosslinks is reported. These networks were prepared by copolymerization of butyl acrylate with different amounts of various difunctional comonomers which yield crosslinks of 4, 7, 10, and 16 bonds in length. The efficiency of the comonomers in crosslinking is low, improving with increasing length of the chain between their unsaturated endgroups. Analysis of a large number of stress–strain data obtained at elongations between 2 and 8% elongation showed that in this deformation range the stress–strain relation based on the statistical theory of elasticity represents the data better than does Hooke's law or the Mooney-Rivlin relation. It was found that the relation between the modulus at small deformations and the swelling ratio of the various samples inindependent of the length of the crosslinks. Also the shapes of the Mooney-Rivlin curves are the same for all networks. Furthermore, the creep behavior of various networks with different crosslink lengths is the same for networks compared at the same elastically effective chain concentration. It is concluded that the lenght of the crosslinks, at least up to 16 bonds, does not affect the elastic response of polymer networks. |
