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Stress−strain relations and strain-induced crystallization (SIC) of unvulcanized and vulcanized states of natural rubber (NR) and synthetic polyisoprene (IR) were studied using synchrotron X-ray at various temperatures from −50 to +75 °C. Unvulcanized IR is a polymer melt that shows a viscous response with yield stress that is related to entanglement and no SIC at 25 °C. However, unvulcanized IR shows SIC at 0, −25, and −50 °C. Entanglements in unvulcanized IR become pivots to align chains and induce crystals at low temperatures. On the other hand, unvulcanized NR shows SIC and stress upturns in stress−strain relations at 25 °C. Since a permanent set is observed after large extension and retraction, unvulcanized NR has a pseudo end-linked network. The pseudo end-linked networks make entanglements as permanent entanglements and show stress upturn and SIC. Vulcanization makes IR to a rubber which shows a stress upturn and SIC by chemical bond network. The stress of vulcanized NR and IR appear almost the same at strains less than 3.0, however the stress of vulcanized NR is much higher than vulcanized IR beyond strain 3.0. The onset strain of SIC of vulcanized NR is much smaller than vulcanized IR. This different behavior is caused by the pseudo end-linked network. The stress in stress−strain relation at higher temperatures is significantly lower than the stress at lower temperatures. This tendency does not seem to follow the theory of rubber elasticity. The onset of SIC delays the upturn of stress as a shoulder or plateau in the stress−strain relation. SIC contributes to the stress, even though the stress smoothly increases with strain. At higher strain, SIC become big network points to bind many chains and reduce the limit of extensibility. The effect of SIC and the limited extensibility to the stress is not distinguishable.

The phase behavior of poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) copolymers near the styrene-rich network phase window was examined through the use of neat triblock copolymers and copolymer/homopolymer blends. Both end-block and middle-block blending protocols were employed using poly(isoprene) (PI), poly(methyl methacrylate) (PMMA), and poly(styrene) (PS) homopolymers. Blended specimens exhibited phase transformations to well-ordered nanostructures (at homopolymer loadings up to 26 vol % of the total blend volume). Morphological consistency between neat and blended specimens was established at various locations in the ISM phase space. Copolymer/homopolymer blending permitted the refinement of lamellar, hexagonally packed cylinder, and disordered melt phase boundaries as well as the identification of double gyroid (Q 230 ), alternating gyroid (Q 214 ), and orthorhombic (O 70 ) network regimes. Additionally, the experimental phase diagram exhibited similar trends to those found in a theoretical ABC triblock copolymer phase diagram with symmetric interactions and statistical segments lengths generated by Tyler et al.