Effect of Rotaxane-Cross-link (2) Property of Cross-linked Polymers Synthesized using Low Molecular Weight Rotaxane Cross-linkers

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.