Mikihiro Hayashi

Design and properties of supramolecular polymer gels

Supramolecular polymer gels are precisely designed physical gels brought together by reversible secondary interactions to form three dimensional networks of melt macromolecules. Generally, they differ from supramolecular gels because they are comprised of polymers instead of low molecular weight compounds. Recently, much effort has focused on designing supramolecular polymer gels and related materials with excellent properties; indeed, improvements have been made in their supramolecular interactions, complementarity in the non-covalent bonding units, the nature of the macromolecular building blocks, and strand elasticity of supramolecular polymer networks. Owing to the precise molecular design, they represent nanophase separation and characteristic viscoelasticity. Here, we review supramolecular polymer gels in terms of molecular design, morphology, and rheology. We also discuss future directions in practical application of supramolecular polymer gels.

Simple preparation of supramolecular polymer gels viahydrogen bonding by blending two liquid polymers

Preparation of supramolecular polymer gels based on simple molecular design was demonstrated by blending carboxyl-terminated telechelic polymers and poly(ethyleneimine), where balance of an attractive force due to hydrogen bonding and a repulsive force induced by phase separation between polymers has been found as a key factor of supramolecular gelation.

Highly Extensible Supramolecular Elastomers with Large Stress Generation Capability Originating from Multiple Hydrogen Bonds on the Long Soft Network Strands

Highly extensible supramolecular elastomers are prepared from ABA triblock-type copolymers bearing glassy end blocks and a long soft middle block with multiple hydrogen bonds. The copolymer used is polystyrene-b-[poly(butyl acrylate)-co-polyacrylamide]-b-polystyrene (S-Ba-S), which is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Tensile tests reveal that the breaking elongation (εb ) increases with an increase in the middle block molecular weight (Mmiddle ). Especially, the largest S-Ba-S with Mmiddle of 3140k, which is synthesized via high-pressure RAFT polymerization, achieves εb of over 2000% with a maximum tensile stress of 3.6 MPa, while the control sample without any middle block hydrogen bonds, polystyrene-b-poly(butyl acrylate)-b-polystyrene with Mmiddle of 2780k, is merely a viscous material due to the large volume fraction of soft block. Thus, incorporation of hydrogen bonds into the large molecular weight soft middle block is found to be beneficial to prepare supramolecular elastomers attaining high extensibility and sufficiently large stress generation ability simultaneously. This outcome is probably due to concerted combination of entropic changes and internal potential energy changes originating from the dissociation of multiple hydrogen bonds by elongation.

Thermal stability enhancement of hydrogen bonded semicrystalline thermoplastics achieved by combination of aramide chemistry and supramolecular chemistry

Thermo-stability enhancement of supramolecular thermoplastics is a meaningful task to enable more application for their usage at high temperatures. An inspiration from aromatic polyamide (aramide) led us to prepare multi-block semicrystalline supramolecular polymers bearing an amorphous dicarboxylic central block and end caps composed of a hydrogen bonding unit (UDETA) and an aramide unit (NHCO-phenyl ring-OCHN). We also prepared three other semicrystalline materials to demonstrate thermal property tuning by simply varying the end caps. The thermal properties of the semicrystalline compounds, including glass transition temperature (Tg) and melting point (Tm) measured by differential scanning calorimetry (DSC), decomposition temperature (Td) measured by thermogravimetric analysis (TGA), and softening temperature (Tsoftening) measured by dynamic mechanical analysis (DMA), were systematically varied depending on the thermal features of the end caps. Especially, Tm and Td were found to be higher than 200 °C and 400 °C, respectively, when both hydrogen bonding and aramide fragments were present. Melt viscosity investigated by rheology was lower than 1 Pa s for each compound due to the low molecular weight of the components (nearly 1200 g mol−1 or less), which is desirable for practical melt processing. Interestingly, shear thinning behavior was observed only in the aramide unit incorporated compound among all the compounds. This indicates a highly clusterable nature of the aramide fragments, which was also supported by the data of its larger flow activation energy than other compounds bearing no aramide fragments. Between Tg and Tm, a large elastic plateau region was observed in the DMA measurements for all compounds, despite their low molecular weight, meaning that the flexible strands are effectively connected into a network through crystallized end-capping groups.

αN-Heterocyclic Carbene Initiated Anionic Polymerization of (E,E)-Methyl Sorbate and Subsequent Ring-Closing to Cyclic Poly(alkyl sorbate)

A diene-based cyclic polymer has been synthesized by the anionic polymerization of methyl sorbate (MS) by an N-heterocyclic carbene (NHC) in the presence of a bulky aluminum Lewis acid. We first polymerized methyl sorbate (MS) initiated by NHC in N,N-dimethylformamide (DMF) at 25 °C, poly(MS) with a number-average molecular weight (Mn) of 3.5 × 103 (Mw/Mn = 2.1) was obtained with a conversion of 93%. The structure was confirmed by 1H and 13C NMR and IR spectra, which revealed that the propagation proceeded via 1,2-addition as well as 1,4-addition. Although the polymerization did not occur in toluene in the absence of any additive, quantitative monomer consumption was observed in the presence of methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) to afford the poly(MS) with a 1,4-trans structure, 86% of threo diastereoselectivity, and a Mn of 23.0 × 103 with narrow molecular weight distribution (Mw/Mn = 1.17). From the matrix assisted laser desorption/ionization (MALDI-TOF) mass spectra of poly(MS) and the hydrogenated analogue, ring-closing occurred by nucleophilic attack of the anionic propagating center into the adjacent carbon of the α-terminal imidazolimium group to afford cyclic poly(MS). The cyclic formation in the present synthesis system was confirmed by DSC and viscosity measurements.

Synthesis of sulfone-containing non-ionic polyurethanes for electrophoretic deposition coating

AbstractThe desire to develop a sustainable society has recently inspired polymer chemists to explore functional polyurethane materials because of their versatile material shape and thermoplasticity. To develop further functionalities of polyurethane materials and manipulation methods, here, we report the synthesis and a new method for coating non-ionic polyurethanes containing sulfonyl groups with utilizing electrophoretic deposition. The polyurethanes were synthesized via polyaddition of methylenediphenyl 4,4′-diisocyanate (MDI) with 2,2′-thiodiethanol in the absence or presence of triethylene glycol (TEG) as the soft ternary segment of the polymer, followed by oxone oxidation. The electrophoretic behaviors of the polyurethanes toward a stainless-steel electrode were investigated, and the peeling resistance and scratch resistance of a polyurethane film coated on a plate were evaluated by cross-cut adhesion and pencil hardness tests, respectively. These tests revealed that incorporation of soft TEG segments at an appropriate fraction can enhance both peeling resistance and scratch resistance. We also tested the enhancement in the transparency of the coated films, which do not lose their favorable peeling resistance and scratch resistance in the process, by replacing the aromatic diisocyanate component (MDI) with an alicyclic diisocyanate, dicyclohexylmethane 4,4′-diisocyanate (HMDI).A new manipulation technique of polyurethane materials via electrophoretic deposition (EPD) is proposed. Polyurethanes with sulfonyl groups are synthesized for the EPD coatings on a stainless-steel electrode plate at the anode side selectively. The coating properties, including peeling resistance, scratch resistance, and transparency, are improved by optimizing soft segment fraction and also by reducing aromaticity of the polyurethanes.

Macromol. Rapid Commun. 8/2016

Back Cover: Highly extensible supramolecular elastomers with large stress generation ability can be prepared from large ABA triblock copolymers bearing hydrogen-bonded B soft block. The large stress is induced by extension of both network strands and hydrogen bonds on the strands while stress concentration at glassy domains is avoided by hydrogen bond breaking, attaining high extensibility. Further details can be found in the article by M. Hayashi,* A. Noro,* and Y. Matsushita on page 678.