An experimentalist's view of the physics of rubber elasticity

The studies relating to the issues and future challenges of the physics of rubber elasticity are presented. The studies are concentrated in the determination of the form of elastic free energy governing the stress-strain relations in cross-linked rubbers. The structural parameters such as the number of elastically effective network strands and junctions of a rubber are characterized to assess the molecular weight theories of the elastic free energy. The trapped entanglements formed in the crosslinking stage of rubber is not disentangled by swelling because the network topology is fixed upon crosslinking. The small-angle neutron scattering technique shows that the single-chain form factor of the labeled constituent elastic chains in polymer networks is a function of the uniaxial stretching strain. The finite chain-length effects of the short chains in bimodal polymer networks lead to increased stress at rubber break.