Note in 2020

A series of ester-functionalized polythiophenes (P3OETs) with precisely controlled head-to-tail (HT) ratios was synthesized via palladium-catalyzed direct arylation polycondensation (DArP). The ionization potentials and optical bandgaps of P3OETs decreased as their HT ratios increased because of the increased backbone coplanarity and extensive π-electron delocalization. The method of precisely controlling the regioregularity and HT ratio can contribute to the design of new polythiophene derivatives with enhanced electronic functionality.

Poly(γ-glutamic acid) (PGA) is a biopolymer produced by Bacillus spp. via the γ-amide linkages of d- and/or l-glutamate. PgsB, PgsC, and PgsA are the minimum protein set required for PGA production in B. subtilis, and PgsE improves PGA productivity. Analysis by size-exclusion chromatography combined with multiangle laser light scattering revealed that the molecular weight of PGA was M_w = 2,900,000 g mol⁻¹ or predominantly M_w = 47,000 g mol⁻¹ in preparations derived from B. subtilis cells with or without pgsE, respectively. PgsE may be required to increase the apparent molecular weight of PGA.

We prepared the chemically crosslinked, cylindrical thermoresponsive poly(N-isopropylacrylamide) gels with changing the contents of reversible addition-fragmentation chain transfer (RAFT) agent. The environment in the gel was estimated by using a hydrophobic fluorescence probe. While the equilibrium swelling ratios were comparable, the deswelling response became fast as the content of RAFT agent increased with the formation of “bubble pattern”. This result indicates that the PNIPAAm gels prepared by RAFT still have spatial defects. In addition, the cooperative diffusion coefficients in swelling process of the gels prepared by RAFT polymerization were estimated.

The synthesis of 100% ¹³C-labelled poly(propylene carbonate) from the completely alternating copolymerization of propylene oxide (rac-PO and R(+)PO) and ¹³CO₂ is reported. The prepared copolymers were shown to be regioselective with predominately head-to-tail (HT) connectivity. The infrared absorption of the polycarbonate in the \(v_{{\mathrm{co}}_{\mathrm{3}}}\) region is red-shifted by 45 cm⁻¹ from the polymer prepared from ¹²CO₂. This shift in frequency allows for the observation of v_NO modes of incorporated dinitrosyl metal complexes.

The synthesis of a novel conjugated polymer containing fused pyridinium units in its main chain is reported. A precursor polymer possessing pyridine and tetrafluorophenylene moieties was reacted in the presence of Lewis acid additives to promote the intramolecular nucleophilic aromatic substitution (S_NAr) reaction. The polymer reaction with BE₃-OEt₂ gave a product polymer soluble in polar organic solvents, and the successful formation of fused pyridinium ring structures was spectroscopically confirmed. The electrochemical and optical properties of the synthesized polymers were also investigated.

A nitrile N-oxide-functionalized polypeptide was synthesized by a two-step method involving the combination of ring-opening polymerization of an amino acid N-carboxyanhydride (NCA) monomer using a primary amine initiator containing a nitroalkane group and a subsequent terminal conversion. The formed peptide was fully characterized by NMR, FT-IR, and MALDI-TOF MS measurements. The catalyst-free grafting reaction of the formed functionalized peptide with rubbers containing double bonds was achieved with high efficiency via an environmentally benign process. These results surely contributed to the development of novel peptide-grafted polymers.

In this report, we evaluated the interplay between molecular weight and mass ratio of polymer during development of viscoelastic properties in HA/FmocFF hybrid supramolecular hydrogels. Rheology was the main tool to assess this complex relationship and the kinetics of network formation during self-assembly were correlated with inherent material properties. Formation of long-rang elastic interactions, ductility and plastic flow were strongly dependent on both size and concentration of polymer, providing a convenient application window to tune the flow properties of the hybrid hydrogels according to the intended application.

Chitin nanofibers were prepared from purified crab-shell chitin particles by repeated high-pressure homogenization in water. AFM images showed that the chitin nanofibers had heterogeneous network structures. X-ray diffraction patterns showed that both the crystallinity index and crystal width of the original α-chitin decreased by nanofibrillation. Solid-state ¹³C-NMR spectra showed that all C6–OH groups had the gauche–gauche conformation. The degree of N-acetylation increased from 0.83 to 0.98 by nanofibrillation, while the weight-average molar masses of the original chitin and chitin nanofibers were 271,200 and 165,500, respectively.