Research articles

A streamlined access to end-functionalized thermoresponsive polymers

In this study, novel water-soluble polyimides and hydrogels were synthesized and evaluated. The water-soluble polyimides were synthesized from biobased 4-aminocinnamic acid dimer and appropriate tetracarboxylic dianhydrides by reaction with aqueous potassium hydroxide. A polyimide hydrogel was prepared using a crosslinking agent with 4-aminophenylalanine or 4-aminocinnamic acid dimer, which are also biobased amino acids, resulted in a fully biobased polyimide hydrogel. This hydrogel exhibits stimulus responsiveness, accompanied by a pH-dependent volume change because of the effect of carboxylate group derived from the polyimide side chain and crosslinking agent.

The higher negative Seebeck coefficients (S) at 30 °C of as-received carbon nanofibers (CNFs) with respect to their polypropylene carbon nanofiber (PP/CNF) melt-mixed composites are explained by a slight electron donation from the outer graphitic shells of the CNFs to the PP molecules. Our study denotes that, contrary to expectations, insulating polymers may play a non-negligible role on the final S-values of conductive polymer composites composed of carbon-based nanostructures.

Block co-oligomers have gained attention for fine and precise control of self-assembled nanostructures. In this study, we investigated the enzyme-catalyzed synthesis of block co-oligomers composed of cello-oligosaccharide and oligo(ethylene glycol) (OEG) chains. The propagation of cello-oligosaccharide chains from bifunctional OEG primers with d-glucose or cellobiose ends, namely, glycosyl acceptors was systematically analyzed. It was plausible from systematic characterizations that diblock and triblock co-oligomers were produced by using the respective primers.

The thin film structures and tribological properties of aqueous solutions of a silicone-based amphiphilic block copolymer confined between mica surfaces were investigated using the surface forces apparatus. Experiments were performed for three copolymer concentrations; the effect of concentration on the structures and properties was evaluated. All the concentrations exhibited good lubricity (friction coefficient on the order of 10⁻⁵). However, precise comparison between concentrations revealed some differences in the molecular friction mechanisms, which were discussed from the perspective of the dissolution states of copolymers in the solutions and adsorbed/sliding conformations.

We demonstrate the facile tuning of uniform Bragg reflection color from red to blue by uniaxial compression of gel films containing single-crystalline loosely packed colloidal crystals. The tuned colors can be fixed by photopolymerization of a polymer precursor solution contained in the compressed gel films.

We evaluated the thermal stability of a molecularly stepped poly(methyl methacrylate) (PMMA) substrate prepared by thermal nanoimprinting and PMMA isolated chains deposited on it by in situ high-temperature atomic force microscopy. The imprinted PMMA surface and isolated PMMA chains on it could be observed at the molecular level up to the glass transition temperature (T_g) of the bulk PMMA and no significant decrease in T_g was observed. The significant thermal stability of them is unexpected and differs from our present understanding of the polymer surfaces.

Selective adsorption of trialkylaluminums (R₃Al) in modified methylaluminoxane (MMAO) onto crosslinked terpolymer bearing bulky phenoxy groups was performed. The phenoxy groups on the terpolymer can more selectivity react with R₃Al than the hydroxy groups on SiO₂, and some R₃Al was physically adsorbed into the terpolymer. As a result, more efficient removal of R₃Al from MMAO solution was achieved. The propylene polymerization using terpolymer-treated MMAO as a cocatalyst was free from chain transfer reaction, which is generally derived from the residual R₃Al.

Near-infrared (NIR) absorptive and emissive poly(p-phenylene vinylene) (PPV)-type π-conjugated polymers based on hypervalent tin-fused azobenzene (TAz) complexes were demonstrated. The synthesized polymers, TAz-PPVs, showed absorption and emission in wavelength regions of >750 and 810 nm in diluted solution, respectively, because of the inherent narrow-energy gap of TAz complexes originating from the three-center four-electron (3c-4e) bond and nitrogen–tin (N–Sn) coordination. Through this research, we revealed that π-conjugated systems including hypervalent bonds were able to expand π-conjugation.

Over the past two decades, intensive efforts have been devoted to the development of group-10 metal catalysts, especially nickel and palladium ligated by unsymmetric bidentate ligands aimed at the copolymerization of olefins with polar monomers. Here we synthesized a palladium complex bearing a methoxyethoxygroup and applied it to the copolymerization of ethylene and methyl acrylate. Higher incorporation of methyl acrylate was detected in the presence of lithium borate such as LiBAr^F₄. The effect was limited to lithium, and the counteranion also affected the catalyst performance.

Scaling relations of pulling translocation of a polymer globule through nanopores is studied by using the Langevin dynamics simulations. Under a constant pulling force, the scaling exponent is dependent on the intrapolymer interaction strength. Whereas under a constant pulling speed, it is independent of the intrapolymer interaction strength for sufficiently long polymer chains. The conformational changes of the polymer chain during the translocation and the entropic and enthalpic forces due to the straight conformation at the trans side play important roles on the pulling translocation of a polymer globule.

We estimated the configurational heat capacity (C_config) of polyisobutylene (PIB), isobutane and 2,2,4-isomethylpentane above the glass transition temperature by reproducing the heat capacity in the solid state using molecular vibration analysis. This is the first time to estimate the C_config of polymer. The C_config decreased with increasing temperature for the three substances in this study. This is a similar pattern as the C_config of molecular glass from a simple molecular structure. Considering that the configuration entropy becomes a constant value at the high temperature limit because the molecules constituting the substance can take any configuration and orientation, it is considered reasonable that the C_config approaches zero at the high temperature limit.

Lignosulfonate is one of the major industrial products from wood. To utilize this compound as a moldable and strong material, we prepared a complex of lignosulfonate with cationic polyelectrolytes and reducing sugars. This complex contains two different crosslinking structures, i.e., ionic crosslinking between lignosulfonate and cationic polyelectrolytes and covalent crosslinking via the Maillard reaction of amino groups with reducing sugars. The coexisting of two different crosslinking greatly improved mechanical strength, Young’s modulus, water resistance, and adhesive strength compared with solely crosslinked complexes composed of the same ingredients.

The precise synthesis of poly(alkenyl boronate)s was achieved through RAFT polymerization of isopropenyl boronate pinacol ester (IPBpin) and subsequent terminal olefination by cobalt catalysis. Experimental and computational investigation on the compatibility of IPBpin with chain transfer agents revealed its conjugated-monomer type behavior that is ascribed to empty p-orbital of boron. Terminal olefination in post-polymerization reaction improved the stability of resulting polymers, enabling the analysis for molecular structure of poly(IPBpin) by MALDI-TOF-MS spectroscopy as well as thermal properties by DSC.

The oxidant addition time and polymerization time were varied during the synthesis of oligo(3-methoxythiophene), and the effect of such polymerization conditions on the physicochemical properties of the oligomer and its cast films was investigated. The polymerization conditions changed the oligomer molecular weight and the amount of edge-on lamellar crystallites in the films and, in turn, affected the color and gloss of the films. The obtained results are expected to facilitate the fabrication of conductive oligo(3-methoxythiophene) films with tunable color and metal-like luster for diverse applications.

The copolymerization of β-substituted acrylates (i.e., crotonates and a cinnamate) using an organo-catalyzed group-transfer polymerization system with N-(tert-butyldimethylsilyl)bis(trifluoromethanesulfonyl)imide (Tf₂NSi^tBuMe₂) and 1-methoxy-1-(tert-butyldimethylsiloxy)-2-methyl-1-propene (^tBuMe2SKA) was investigated. The tert-butyldimethylsilyl moiety served as an effective means for suppressing the termination reactions of the GTP system. One-stage and two-stage copolymerization strategies employing different monomer feed methods were evaluated and gave random and block copolymers, respectively. The glass-transition temperatures of the prepared copolymers varied significantly depending on the comonomer used during the synthesis.

This study presents a facile method for preparation of water-soluble molecular complexes between carboxylic acid-functionalized multiwalled carbon nanotube and poly(2-methacryloyloxyethyl phosphorylcholine) (MWCNTs/PMPC) by hand grinding. MWCNTs could be solubilized in aqueous environment with higher suspended concentrations when increasing polymer concentration and pH of the solution. MWCNTs/PMPC adsorbed light and induced heat generation to reach the temperature required for photothermal therapy (PTT) when the complexes were irradiated by near-infrared (NIR) at a wavelength of 808 nm. The water-soluble MWCNT complex covered by biocompatible PMPC is a promising candidate for PTT application.

A novel thermoresponsive diblock copolymer of methyl poly (ethylene glycol)-b-poly (O-benzyl-L-threonine) was synthesized. The copolymer solutions exhibited gel-to-sol UCST transition behavior with temperature. The gel-to-sol transition was due to the disassembly of the initial β-sheet layered nanoassemblies that induced the transformation of self-organized morphology from nanosized fibrils to spherical aggregates.

pH- and thermoresponsive polymer bearing pendant tertiary amino groups was grafted onto the surface of Resovist (PDMA@Rv). At pH 5.4, the grafted-polymer became hydrophilic, and the size of PDMA@Rv remained constant, irrespective of temperature. PDMA@Rv formed aggregates and showed lower critical solution temperature behavior above pH 7. PDMA@Rv contained a larger number of core particles of iron oxide than Resovist, which reduced the initial magnetic susceptibility due to the interaction of the core magnetic particles inside PDMA@Rv.

The confinement effect on the chain conformation and crystallization behavior of poly(ethylene oxide) (PEO) in electrospun nanofibers was investigated. The PEO chains in electrospun nanofibers were tightly packed and exhibited a zigzag conformation. Increasing the fiber diameter reduced the packing of polymer chains, resulting in increases in the melting temperature and crystallite size. Thermal treatment relaxed the stretched chains, which induced a change from the metastable zigzag conformation to a stable helical conformation. Additionally, the melting temperature, degree of crystallinity, and crystallite size increased with increasing annealing temperature.