Gum and black-filled double networks of cis-1,4-polyisoprene crosslinked with sulfur donors: Part I. Tensile properties

Gum and black-tilled double networks of cis-1,4 polyisoprene, crosslinked with sulfur donors, have been prepared by first partially curing sheets, then stretching them and completing cure. Double networks are anisotropic and exhibit a residual extension ratio λ(r), which is higher for filled compared to gum samples. Additionally, double networks of filled specimens have higher anisotropy than gum counterparts, presumably because carbon black promotes chain alignment and strain-crystallization. Tensile specimens cut parallel to the stretch direction are stiffer, less extensible, and sometimes stronger than simple isotropic networks, while perpendicular specimens have stress-strain responses much like that of the isotropic control.