A new thermodynamically stable, aperiodic "bricksand-mortar" (B&M) cellular mesophase structure is reported in PS 1 -b-(PI-b-PS 2 ) 3 miktoarm copolymer and PS homopolymer blends [PS 1 , long polystyrene; PI, poly(isoprene); PS 2 , short polystyrene], where PS comprises discrete hard "bricks" and PI the continuous soft "mortar". The mesophase is unique in its extreme domain volume fractions, its lack of positional order, and quasi-long-range orientational order. On the basis of this unusual mesophase structure, a series of PS-based thermoplastic elastomers are realized, combining rigidity from an exceptionally high content of discrete glassy PS domains (up to 82 wt %) and high extensibility with recoverable elasticity from a low content of continuous rubbery PI (down to 18 wt %). The new elastomers show sharp yielding behavior while maintaining good elasticity at large strains. Tensile-SAXS experiments reveal that voiding plays an important role for the mechanical behavior and voids can open/close reversibly with/without loading. Plastic deformation only results in a slight loss of recoverable elasticity.

We have investigated the structural changes occurring in highly crosslinked and carbon-black filled natural rubber under uniaxial extension by small-and wide-angle X-ray scattering using synchrotron radiation. The experiments focused on strain-induced crystallization (SIC) and nanocavitation and were carried out on a model series of materials as a function of temperature and aging conditions. We find that for all materials both SIC and cavitation decrease markedly with temperature and aging. However, the presence of carbon black filler shifts the ceiling temperature where SIC is observed to at least 120 C, presumably by a nucleating effect, maintaining the high strength of the elastomers. Interestingly, although in pure elastomers, the cavitation strength decreases with temperature, we find that in these filled elastomers the critical stress for the onset of cavitation increases significantly with temperature strongly suggesting that cavitation is due to the local confinement between fillers and supporting the idea of a glassy layer near the filler. Aging for 10 days at 110 C in oxygen-free conditions decreases both SIC and cavitation and reduces the strength of the elastomer at high temperature. This is attributed to the formation of sulfur side chains hindering the crystallization.Such conditions are found between steel plies of the carcass of a truck tire. The need to bond to the steel cord imposes high levels of added sulfur and therefore a high crosslink density, while the position of the rubber inside the tire results in nonoxidizing aging conditions and a temperature of the order of 100 C for highway driving. The combination of high stress, high temperature, and high confinement makes this spot a critical safety spot for the tire and materials requirements are particularly stringent.The main results of previous studies on SIC of natural rubber can be summarized as follows. SIC is a thermodynamically driven phenomenon triggered by a decrease in entropy of the polymer chains as they are stretched, which reduces the barrier to form crystals. Within that framework, the higher the deformation of the chains and the lower the temperature, and the more chains can crystallize along the stretching direction. This has been demonstrated in lightly crosslinked unfilled natural rubbers. However, the effect of increasing the crosslink density is less obvious to interpret. For peroxide crosslinked natural rubber increasing the crosslink density clearly favors SIC in terms of onset of crystallinity and the crystallization "rate," that is, the increase in crystallinity with increasing stretch λ. 7,15 However, for the much Additional Supporting Information may be found in the online version of this article.