Study of the Uniaxial Deformation of Rubber Network Chains by Small Angle Neutron Scattering

Abstract

Small angle neutron scattering (SANS) measurements were performed on poly(isoprene) networks at different uniaxial strains, i.e., 1.0 ≤ λ (extension ratio) ≤ 2.1. The networks were prepared from anionically polymerized, α,ω,-dihydroxy-poly(isoprene) precursors (H-chains) and the corresponding poly(isoprene-d₈) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrofuran solutions by trifunctional crosslinkers, tri-isocyanates. The two components of the radius of gyration of elastic strands, parallel and perpendicular to the strain axis, were determined from the SANS data of the networks with 8% and 15% D-chains. Two molecular weights of D-chains, 26,000 and 64,000, crosslinked with approximately the same molecular weight H-chains (29,000 and 68,000 respectively) were examined for the deformation behaviors. From the observed changes in the parallel and perpendicular components of the radius of gyration relative to macroscopic extension ratio, after appropriate correction for the dangling chain contributions, the chain extensive deformation is found to follow a behavior intermediate between the junction affine model and the phantom network model which allows unrestricted fluctuations of network junctions. On the other hand, the chain contractive deformation follows closely the chain affine model, indicating an asymmetry between extensive and contractive chain deformation. In either case, the deformation behavior is found to be the same for the two molecular weights.

On leave from the School of Materials Science, Toyohashi 440, Japan.

Work was performed in part as a NRC postdoctoral fellow at N.B.S.;

Work was performed during the residence at N.B.S. as a NRC postdoctoral fellow;