Shin-ichi Kihara

Supramolecular Porphyrin Copolymer Assembled through Host–Guest Interactions and Metal–Ligand Coordination

Bisporphyrin cleft molecule 1 Zn possessing a guest moiety assembled to form supramolecular polymers through host-guest interactions. Bispyridine cross-linkers created interchain connections among the supramolecular polymers to form networked polymers in solution. Solution viscometry confirmed that the cross-linked supramolecular polymers were highly entangled. Frequency-dependent linear viscoelastic spectroscopy revealed that the supramolecular polymers generated well-entangled solutions with associating and networking polymers, whereas the solid-like aggregates moved individually without breaking and reforming structures below the transition temperature of 9.6 °C. Morphological transition of the supramolecular polymers was evidenced by AFM images; the non-cross-linked polymer resulted in wide-spread thin networks, while the cross-linked networks produced thicker worm-like nanostructures. The supramolecular networks gelled in 1,1,2,2-tetrachloroethane, and an elastic free-standing film was fabricated with a Youngs modulus of 1 GPa.

Supramolecular Copolymerization by Sequence Reorganization of a Supramolecular Homopolymer

The homopolymeric sequence formed by the head-to-head association of tetrakisporphyrin 1 is completely dissociated by the competitive association of the ditopic guest G2, resulting in the supramolecular copolymer poly-1⋅G2 with an alternatingly repeating host-guest sequence. The 1:1 stoichiometry of 1 and G2 is confirmed by a Job plot using UV/Vis titration and diffusion-ordered NMR spectroscopy (DOSY). The solution viscometry for poly-1 and poly-1⋅G2 suggests that the supramolecular chain of poly-1 behaves like a rod, whereas the supramolecular copolymer chain of poly-1⋅G2 behaves like a swelled fat chain, which is entangled in the semi-dilute regime. Atomic force microscopy shows that the supramolecular polymer poly-1⋅G2 is highly oriented through the interdigitation of the long alkyl chains.

Reversible star assembly of polyolefins using interconversion between boroxine and boronic acid

Synthetic methods for star-shaped polyolefins have been strongly desired for a long time because they would show large differences in processability and surface properties compared to linear polyolefins. However, present reported synthetic methods are mostly limited to the synthesis of highly branched star polyethylenes and there have been no examples of reversible star assemblies. In this work, we have demonstrated the synthesis of boronic acid end-functionalized polyolefins by a living polymerization system and their reversible star assembly according to a boronic acid–boroxine interconversion. Multiple boron atoms were successfully incorporated onto the chain end of the polymer by the sequential addition of a boronic acid-containing olefin and the other monomer, and the reversible star assembly was confirmed by NMR and GPC measurement. The star poly(norbornene-co-1-octene) prepared by this method showed a highly elastic property, whereas the corresponding linear non-functionalized copolymer was a highly viscous material.