Assuming the degradation of styrene-butadiene rubber (SBR) during its practical usage, the accelerated weathering tests were conducted with various pre-strains. Although the isotropic narrower cracks form under no pre-strain (0% strain), the wider crazes orients perpendicular to the pre-strained direction under 20% pre-strain. The larger prestrain of 40% induces the vertical penetration of these crazes vertically from the exposed surface. The cross-sectional observation under 80% pre-strain suggests that the further craze propagation finally tears the sample inside. Correspondingly, both of breaking strength and strain significantly decreased with increasing pre-strain. In contrast, the post-strain applied after the accelerated weathering test under no pre-strain gave only the middle cracks, suggesting that the initial narrower cracks grow into the latter wider crazes during the accelerated weathering tests under prestrained. The origin of such initial narrower cracks is attributable to the pre-strained structure before the accelerated weathering test, which was confined by scanning probe microscopy (SPM) observation. The distribution of carbon black (CB) mixed in the base rubber was biased even at the low strain. The characteristic phase separation of CB domains gave the narrower cracks during the accelerated weathering test, which further grow into the wider crazes and inside tearing.

The author proposes the essential features of wear of rubber, where the rubber wear is related inseparably to abrasion pattern formation generated by stick-slip motion during frictional sliding of the rubber. Initial micro-cracks in this process are induced by the micro-vibration of high frequency, which grow up to the abrasion patterns accelerated by the stick-slip motion. Thus, the wear of the rubber is just understood to be the process of the formation and separation of ridges of the abrasion pattern. The author newly induces “Wear-abrasion pattern diagram”, where the rate of wear V 4 is connected directly to the distance between the abrasion patterns Dab with the equation, V 4 =k(Dab) n, n be - ing 1/3 at an early stage and 3.5 for a final steady stage of the wear, k a constant.

We discuss on the effect of rotaxane-cross-link on the mechanical property (i.e. toughening) of the cross-linked polymers, in particular on the mobility effect of the rotaxane components, using [2]rotaxane cross-linkers having low molecular weight axles but not high molecular weight one as mentioned in the previous paper, to evaluate the function of the circumrotatory and flipping mobilities in comparison with the translating mobility of the wheel components at the cross-link points. Independent on the length of the axle component, the low molecular weight axle-containing rotaxane cross-linkers showed good power to strengthen the toughness of the cross-linked polymers. Meanwhile, [3]rotaxane cross-linkers having two crown ether wheels with two polymerizable vinyl groups worked as the excellent cross-linkers to contribute to the toughening of the cross-linked polymers, whereas the axle component had no direct bonding to the polymer chain, being different from that of [2]rotaxane cross-linker. In the latter half of this review, we dealt with macrocyclic cross-linkers which can accept polymer chains in their cavity to form rotaxane-type cross-link. 60-Membered macrocycle possessing two Pd(II) complex units in its cavity functioned as a rotaxane-type cross-linker by accepting two polymer chains possessing the coordinating sites to Pd(II). Cross-linker synthesized by linking two 30-membered macrocyclic Pd(II) complex also showed a similar ability to link two polymer chains to cross-linking.