Volume 54 Issue 2, February 2022

“Breath figure formation” during the casting process of polymer solutions under high atmospheric humidity provides honeycomb-patterned polymer films (honeycomb films) with regularly arranged micropores. The development of production technology for large-area honeycomb films is indispensable for their various applications. Manufacturing equipment consisting of three zones (for casting, humidification, and drying of polymer solutions) for successive formation of large-area honeycomb films was newly designed and constructed. By using this equipment, physicochemical experimental parameters, e.g., the surface temperature of polymer solutions, dew point of the humidification zone, humidification time, and interfacial tension between water and the polymer solution, were effectively changed to optimize the density and size of condensed water droplets. Large-area honeycomb films were formed by a roll-to-roll process. Herein, recent developments in biomedical applications of honeycomb films are described.

Relationship between the primary structures and their properties is recognized as an important research subject for polymer chemists. To make progress in this academic field, innovative synthetic procedures of cyclic polymers are essential. The synthetic strategy has two typical pathways: one is the ring closure of functional linear polymers and the other is ring expansion polymerization using cyclic monomers, an initiator, or a catalyst. This focus review deals with the recent synthetic evolution of cyclic polymers, focusing on our new strategy: ring closing without highly dilute conditions.

We synthesized novel benzoxazine-polymers, poly(1)_230–2000 consisting of rigid phenyleneethynylene and flexible polypropylene glycol (PPG) moieties in the main chain. Resins obtained by cross-linking reaction of poly(1)_230–2000 were thermally as stable as a previously synthesized polybenzoxazine resin containing phenyleneethynylene moieties. Introduction of flexible PPG unit was effective to lower the curing temperature, and enhance mechanical toughness keeping thermal stability.

In this study, stoichiometry-independent Migita–Kosugi–Stille coupling polycondensation was performed between 2,5-bis(trimethylstannyl)thiophene and an ester-functionalized dibromo monomer, bis(2-butyloctyl) 2,5-dibromoterephthalate, to obtain high-molecular-weight π-conjugated poly(phenylene thienylene) (M_n = 16,800). The method uses a 2-fold excess of the dibromo monomer toward the distannylated monomer. Such successful nonstoichiometric polycondensation may be derived from the intramolecular Pd(0) catalyst transfer on the aromatic dibromo monomer after the first coupling reaction between the dibromo monomer and stannylated compounds during polymerization.

We selected a polylactide (PLA) copolymer with poly(ethylene glycol) (PEG) and a urethane capping PLA and prepared various stereocomplex (SC). Depending on the combination of L-isomers and D-isomers, the SCs were classified as Homo-SC, Co-SC, and Multi-SC: Homo-SC by the same polymer chain ends and copolymers, Co-SC by different polymer chain ends and copolymers, and Multi-SC by a mixture of various polymer chain ends and copolymers. Multi-SC showed two broad melting points at around 200 °C, suggesting the various combinations of polymer–polymer interaction in the case of Multi-SC.

Organogel formation was observed immediately during the addition of diisocyanate to a solution of para-substituted bis(3-aminopropyl)hexaisobutyl-substituted cage octasilsesquioxane (T₈ cage) monomer at room temperature when above the critical gel concentrations (C_gs). T₈-polyureas with phenylurea moieties promoted organogel formation in comparison with T₈-polyureas with nonphenylurea moieties. The substitution of methyl groups at the ortho position of the phenylurea groups provided lower C_gs. Increasing the intermolecular interaction between the ureido groups in the T₈-polyurea enhanced organogel formation, which was supported by the FT-IR analysis of the dried gels.

Long-term morphological and chemical stabilities of polypyrrole grains doped with chloride ion or heptadecafluorooctane sulfonic acid in aqueous media (1-year duration) are studied. There were appreciable changes in chemical structure and surface chemistry, although the size and morphology of the polypyrrole primary particles did not change for each grain system. The dopants were released with time, and its rate was slower for the polypyrrole doped with heptadecafluorooctane sulfonic acid, compared to that doped with chloride ion. This should be due to the stronger hydrophobic interaction between polypyrrole and heptadecafluorooctane sulfonic acid.

Hydration and crosslinking in hydrophilic ionic polymers give rise to microstructural features which affect diffusion of water and proton conductivity in them. Crosslinking in these systems gives rise to the presence of crosslink heterogeneities resulting in more-crosslinked domains and less-crosslinked regions. Because of the difference in elasticity between the two regions the polymer matrix swells differentially resulting in anomalous water sorption kinetics. The diffused water is distributed among hydroxyl and sulfonic groups and the crosslinking alters this distribution resulting in an increase in conductivity.

We report a photoresponsive polythiophene derivative containing a photocleavable coumarin group with an octyloxy side chain as a solubilizing group. This polymer enables fabrication of solution-processed polymer film owing to the solubilizing group. Photoirradiation at 313 nm gives the photocleaved side chain, yielding a carboxyl group. Formation of the carboxyl group causes insoluble polythiophene. Change in the solubility provides a photopatterned film through a photomask. In addition, the photocleaved polythiophene film exhibits a 10⁴-fold increase in the electrical conductivity by chemical doping.

Low-molecular-weight amphiphilic block copolymers with controlled architecture represent an interesting manner for safe delivery of siRNAs and hydrophobic anticancer drugs. The tailored synthesis, supramolecular assembly and morphology were investigated using triblock copolymers based on α- and ε-lysine oligomers.

To clarify the role of lateral deformation of condensed polymer surface on cell adhesion, the responses of cell spreading were characterized at a cell culture temperature on the poly(N-isopropylacrylamide)-grafted surfaces with different degree of graft-polymerization (DGP). A clear negative correlation between cell spreading and DGP of PNIPAAm was found regardless of the amount of fibronectin adsorbed on the substrates. The microscopic local strain of the condensed polymers by cellular traction forces was considered to modulate the density distribution of adsorbed adhesive ligands beneath the focal adhesions and the cell spreading.

Bis(indolyl)-coordinated titanium dichlorido complexes were applied for ethylene polymerization. The results showed that [{bis(indolyl)}TiCl₂]₂ activated by modified methyl aluminoxane (MMAO) exhibited ethylene polymerization activity up to 2494 (kg of polyethylene)/(mol of Ti)·h·atm. This activity is comparable to the highest known activity in catalyst systems based on diamido-supported titanium complexes. The [{bis(indolyl)}TiCl₂]₂/MMAO catalyst system was also active for propylene polymerization (344 (kg of polypropylene)/(mol of Ti)·h·atm) to furnish atactic polypropylene.

Natural rubber is a biopolymer with unique features widely used in many industrial applications. It is composed mainly by large high-molecular-weight polymeric chains of cis-1,4-polyisoprene with distinct α-terminal groups, which are thought to give natural rubber its specific features. The second most abundant molecule in natural rubber is L-quebrachitol, a cyclic polyol which function is not clear. Here we studied using atomistic simulations the interaction of L-quebrachitol with the hydrophobic natural rubber and its interaction with specific α-terminal groups, suggesting it binds preferentially with specific α-terminal groups.