Takuya Isono

Organophosphate-catalyzed bulk ring-opening polymerization as an environmentally benign route leading to block copolyesters, end-functionalized polyesters, and polyester-based polyurethane

The ring-opening polymerizations (ROPs) of e-caprolactone (e-CL), δ-valerolactone, 1,5-dioxepan-2-one, trimethylene carbonate, and L-lactide were performed in the bulk using an organophosphate, such as diphenyl phosphate, bis(4-nitrophenyl)phosphate, and di(2,6-xylyl)phosphate, as the catalyst. The ROPs proceeded in a well-controlled manner even under the bulk conditions to afford well-defined aliphatic polyesters, polyester–ether, and polycarbonate with relatively low dispersities. Notably, the amount of the loaded catalyst was successfully reduced when compared to the conventional organophosphate-catalyzed ROP in solution. A kinetic study revealed the controlled/living nature of the present bulk ROP system, which allowed us to produce the block copolymers composed of polyesters, polyester–ether, and polycarbonate in one pot. Syntheses of the end-functionalized poly(e-caprolactone)s (PCLs) and poly(trimethylene carbonate) were successfully demonstrated using alcohol initiators possessing highly reactive functional groups. Furthermore, the α,ω-dihydroxy telechelic PCL-diol as well as the three- and four-armed star-shaped PCL-polyols were also easily obtained by using the polyols as an initiator. Finally, the one-pot synthesis of polyurethane via the ROP of e-CL and a subsequent urethane forming reaction was demonstrated by taking advantage of the dual catalytic abilities of the organophosphate for both the ROP and polyurethane synthesis.

Synthesis of end-functionalized poly(methyl methacrylate) by organocatalyzed group transfer polymerization using functional silyl ketene acetals and α-phenylacrylates

The present study describes the α- and ω-end-functionalization of poly(methyl methacrylate)s (PMMAs) by organocatalyzed group transfer polymerization (GTP) using both functional silyl ketene acetal (SKA) initiators and α-phenylacrylate terminators. The syntheses of structurally defect-free α-end-functionalized PMMAs with hydroxyl, ethynyl, vinyl, and norbornenyl groups (HO-PMMA, HCC-PMMA, H2CCH-PMMA, and NB-PMMA, respectively) were achieved by either the N-(trimethylsilyl)bis(trifluoromethanesulfonyl)imide-(Me3SiNTf2-) or t-Bu-P4-catalyzed GTP of MMA using functional trimethyl SKAs (1a–1d). On the other hand, the ω-end-functionalized PMMAs with ethynyl, hydroxyl, vinyl, and bromo groups (PMMA-CCH, PMMA-OH, PMMA-CHCH2, and PMMA-Br, respectively) were for the first time obtained by the Me3SiNTf2-catalyzed GTP of MMA followed by a termination reaction using functional α-phenylacrylates (2a–2d). All the polymerizations produced end-functionalized PMMAs with controlled molar masses, narrow dispersities, and defect-free polymer structures as designed. The quantitative incorporation of functionalities into the α- or ω-end of the PMMAs was confirmed by the 1H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) measurements.

Intramolecular olefin metathesis as a robust tool to synthesize single-chain nanoparticles in a size-controlled manner

A comprehensive examination of the synthesis of single-chain nanoparticles (SCNPs) from statistical copolymers of n-butyl methacrylate (BMA) and 3-butenyl methacrylate (3BMA), i.e., P(BMA-co-3BMA)s, via the intramolecular olefin metathesis reaction under high dilution conditions is described. The olefin metathesis reaction of P(BMA-co-3BMA) using Grubbs’ 2nd generation catalyst in CH2Cl2 efficiently gave the corresponding SCNPs under mild conditions. We achieved the size-controlled synthesis of the SCNPs by adjusting the following factors: (1) the olefin content in the precursor, (2) the molecular weight of the precursor, and (3) the solvent quality of the reaction medium. The hydrodynamic radius and the intrinsic viscosity of the resultant SCNPs were investigated by DLS and viscometric measurements, respectively, which provided further evidence of SCNP formation with controlled diameters. Furthermore, the above-established intramolecular olefin metathesis approach was successfully applied to poly(acrylate), poly(styrene), and poly(ester) precursors, which proved that the present approach could be applied to a wide range of olefin-containing precursors to give SCNPs with various functional groups.

Synthesis, morphology, and electrical memory application of oligosaccharide-based block copolymers with π-conjugated pyrene moieties and their supramolecules

We report the synthesis, morphology, and field effect transistor memory application of maltoheptaose-based block copolymers, maltoheptaose-block-poly(1-pyrenylmethyl methacrylate) (MH-b-PPyMA), and their supramolecules with (4-pyridyl)-acceptor-(4-pyridyl), MH(4Py-Acceptor-4Py)x-b-PPyMA. MH-b-PPyMA was prepared by the combination of the t-Bu-P4-catalyzed group transfer polymerization and the Cu(I)-catalyzed azide–alkyne cycloaddition reaction. After the thermal annealing process, the MH-b-PPyMA bulk sample underwent microphase separation to form the sub-10 nm periodic self-assembled nanostructure. The self-assembled morphologies transform from the hexagonal cylinder packing to the body-centered cubic sphere arrangement and the disordered spherical nanodomain with the increase of the PPyMA segment length. On the contrary, only the spherical nanodomain was observed in the thermo-annealed thin film samples of both MH-b-PPyMA and MH(4Py-Acceptor-4Py)x-b-PPyMA. The electrical characteristics of the p-type pentacene-based OFET memory device were studied using the thermo-annealed polymer thin film as the electret layer. The MH(4Py-Acceptor-4Py)x-b-PPyMA-based organic field effect transistor (OFET) devices had the high hole mobility of 0.20–1.08 cm2 V−1 s−1 and the ON/OFF current (ION/IOFF) ratio of 107–108, in which the acceptor of the benzo[c][1,2,5]thiadiazole (BT) based device possessed the higher hole mobility than that of the isoindigo-based one due to the more ordered packing pentacene crystals. The memory window (ΔVTH) of the supramolecule-based device was increased with enhancing the 4Py-Acceptor-4Py blending composition, and that of the MH(4Py-BT-4Py)1.5-b-PPyMA10-based device had the largest ΔVTH of ca. 9 V, a long-term retention time greater than 104 s and the high ION/IOFF memory ratio of 106–107 (reading at Vg = 0 V) for more than 100 programming/erasing cycles. Our results demonstrate that the bio-related block copolymers and their supramolecular thin film could be used as electret layers for high-performance nonvolatile flash green memory devices.

Rod-coil type miktoarm star copolymers consisting of polyfluorene and polylactide : precise synthesis and structure-morphology relationship

A series of rod–coil miktoarm star copolymers consisting of poly[2,7-(9,9-dihexylfluorene)] (PF) and polylactide (PLA) arms as the rod and coil segments, respectively, were synthesized by combining the chain-growth Suzuki–Miyaura coupling polymerization and living ring-opening polymerization (ROP). First, PFs having a hydroxyl group at the α-chain end (PF–BnOH) were prepared by the polymerization of 2-(7-bromo-9,9-dihexyl-9H-fluorene-2-yl)4,4,5,5-tetramethyl-1,2,3-dioxaborolane using the initiating system of 4-(tetrahydropyran-2′-yloxymethyl)-iodobenzene/Pd2(dba)3/t-Bu3P. After a couple of chain end modifications, PFs having one, two, and three hydroxyl groups at the α-chain end (PF–OH, PF–(OH)2, and PF–(OH)3, respectively) were obtained with dispersity (Đ) values of less than 1.29. The obtained PF–OH, PF–(OH)2, and PF–(OH)3 were used as the initiators for the organic base-catalyzed ROP of rac-lactide to produce the AB type linear diblock (PF-b-PLA) and AB2 and AB3 type miktoarm star copolymers (PF-b-(PLA)2 and PF-b-(PLA)3, respectively). The self-assembled nanostructures in the thermally-annealed PF-b-(PLA)xs (x = 1, 2, and 3) were evaluated in the bulk by synchrotron small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The PF-b-PLA, PF-b-(PLA)2, and PF-b-(PLA)3 with the PF weight fractions of 0.52–0.56 were found to form poorly ordered PLA cylindrical structures in the PF matrix due to a strong rod–rod interaction of the PF segment. On the other hand, these BCPs with the PF weight fractions of 0.22–0.23 exhibited the hexagonally close-packed cylinder (Hex) morphologies, in which the cylindrical PF phase was embedded in the PLA matrix. More interestingly, the domain-spacing (d) values for the Hex morphologies decreased with the increasing PLA arm number despite each BCP having a comparable molecular weight and PF weight fraction: d = 26.4 nm for PF-b-PLA, d = 21.7 nm for PF-b-(PLA)2, and d = 18.6 nm for PF-b-(PLA)3.

Design and synthesis of thermoresponsive aliphatic polyethers with a tunable phase transition temperature

This paper describes a comprehensive study of the lower critical solution temperature (LCST)-type thermoresponsive properties of various poly(glycidyl ether) homopolymers with a varying side chain structure, molecular weight, and main chain tacticity, as well as their copolymers with a varying monomer composition and monomer sequence. For the initial screening, we prepared nine kinds of poly(glycidyl ether)s by the phosphazene base-catalyzed ring-opening polymerization of glycidyl methyl ether (MeGE), ethyl glycidyl ether (EtGE), glycidyl isopropyl ether (iPrGE), 2-methoxyethyl glycidyl ether (MeEOGE), 2-ethoxyethyl glycidyl ether (EtEOGE), 2-propoxyethyl glycidyl ether (PrEOGE), 2-(2-methoxyethoxy)ethyl glycidyl ether (MeEO2GE), 2-(2-ethoxyethyl)ethyl glycidyl ether (EtEO2GE), and 2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether (MeEO3GE). Among them, poly(MeGE), poly(EtGE), poly(MeEOGE), poly(EtEOGE), and poly(MeEO2GE) (Mn = ca. 5000 g mol−1) were found to exhibit a LCST-type phase transition in water at 65.5 °C, 10.3 °C, 91.6 °C, 41.3 °C, and 58.2 °C, respectively. Although the molecular weight and main chain tacticity had little impact on the phase transition temperature, the side chain structure, i.e., the number of oxyethylene units and terminal alkyl groups, significantly affected the transition temperature. The statistical copolymers composed of MeEOGE and EtEOGE revealed that the transition temperature of the polymer can be desirably customized in between those of the homopolymers by varying the monomer composition. On the other hand, we found that the block copolymer composed of MeEOGE and EtEOGE exhibited a complex thermoresponsive behavior due to its ability to form a micellar aggregate.

Synthesis of lactate (LA)-based poly(ester-urethane) using hydroxyl-terminated LA-based oligomers from a microbial secretion system

D-Lactate (LA)-based oligomers (D-LAOs), consisting of D-LA and D-3-hydroxybutyrate (D-3HB), are biobased compounds which are produced and spontaneously secreted by recombinant Escherichia coli. By supplementing the bacterial cultivation with diethylene glycol (DEG), the oligomers featuring hydroxyl groups at both ends of their structures, the D-LAOs-DEG, can be efficiently biosynthesized. In the present work, we attempted to verify the feasibility of D-LAOs-DEG as building blocks to be assembled into LA-based poly(ester-urethane) via polyaddition reaction with diisocyanate. The polymeric products were demonstrated by SEC and the urethane bound formation in the polymer was determined by FT-IR analysis, indicating that the polymerization was successfully performed. These results suggested that the one-step biosynthesized D-LAOs-DEG are potential substrates for the synthesis of LA-based poly(ester-urethane) and can be further applied to the synthesis of other LA copolymers.

One-Step Production of Amphiphilic Nanofibrillated Cellulose Using a Cellulose-Producing Bacterium

Nanofibrillated bacterial cellulose (NFBC) is produced by culturing a cellulose-producing bacterium (Gluconacetobacter intermedius NEDO-01) with rotation or agitation in medium supplemented with carboxymethylcellulose (CMC). Despite a high yield and dispersibility in water, the product immediately aggregates in organic solvents. To broaden its applicability, we prepared amphiphilic NFBC by culturing strain NEDO-01 in medium supplemented with hydroxyethylcellulose or hydroxypropylcellulose instead of CMC. Transmission electron microscopy analysis revealed that the resultant materials (HE-NFBC and HP-NFBC, respectively) comprised relatively uniform fibers with diameters of 33 ± 7 and 42 ± 8 nm, respectively. HP-NFBC was dispersible in polar organic solvents such as methanol, acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran (THF), and dimethylformamide, and was also dispersible in poly(methyl methacrylate) (PMMA) by solvent mixing using THF. HP-NFBC/PMMA composite films were highly transparent and had a higher tensile strength than neat PMMA film. Thus, HP-NFBC has a broad range of applications, including as a filler material.

Synthesis of μ-ABC Tricyclic Miktoarm Star Polymer via Intramolecular Click Cyclization

Cyclic polymers exhibit unique physical and chemical properties because of the restricted chain mobility and absence of chain ends. Although many types of homopolymers and diblock copolymers possessing cyclic architectures have been synthesized to date, there are relatively few reports of cyclic triblock terpolymers because of their synthetic difficulties. In this study, a novel synthetic approach for μ-ABC tricyclic miktoarm star polymers involving t-Bu-P4-catalyzed ring-opening polymerization (ROP) of glycidyl ethers and intramolecular copper-catalyzed azido-alkyne cycloaddition (CuAAC) was developed. First, the t-Bu-P4-catalyzed ROP of decyl glycidyl ether, dec-9-enyl glycidyl ether, and 2-(2-(2-methoxyethoxy) ethoxy) ethyl glycidyl ether with the aid of functional initiators and terminators was employed for the preparation of a clickable linear triblock terpolymer precursor possessing three azido and three ethynyl groups at the selected positions. Next, the intramolecular CuAAC of the linear precursor successfully produced the well-defined tricyclic triblock terpolymer with narrow dispersity in a reasonable yield. The present strategy is useful for synthesizing model polymers for studying the topological effects on the triblock terpolymer self-assembly.

Unraveling the stress effects on the optical properties of stretchable rod-coil polyfluorene-poly(n-butyl acrylate) block copolymer thin films

We report the synthesis, morphology, and photophysical properties of new conjugated rod-coil block copolymers consisting of poly[2,7-(9,9-dihexylfluorene)] (PF) conjugated rods and soft poly(n-butyl acrylate) (PBA) coils for stretchable light-emitting device applications. The PF-b-PBA thin films could form obvious self-assembled nanofibrillar structures after the solvent annealing treatment. Besides this, both the deformability and optical properties of block copolymers were controllable by varying the PF/PBA ratio. The annealed PF4k-b-PBA7k thin film exhibited pure blue emission with a high photoluminescence quantum yield of over 22.5% under 100% strain, validating the excellent stretchability and promising stability. Furthermore, a stretchable and fluorescent PF-b-PBA based microporous template with tunable regularity can be fabricated through the breath figure method. These results demonstrated that the novel intrinsically deformable and luminescent rod-coil block copolymers could have versatile applications in stretchable light-emitting devices.