This study investigated the impact of oxygen quenching on dark polymerization by changing the atmosphere from nitrogen to air after stopping UV light irradiation. Real-time FT-IR measurements showed that C=C bond conversions of multifunctional monomers (diurethane dimethacrylate, dipentaerythritol penta-/hexa-acrylate) and a reactive polymer in which the functional group was acrylate were 0.01–0.04, greater than that in an environment of continuous nitrogen purging, when the UV irradiation dose larger than 3 mJ/cm² with a photoinitiator 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime) (OXE01). Kinetic analysis of the dark polymerization elucidated that it was promoted when the polymerization and termination reaction rates were controlled by the diffusion of the C=C bond groups. Exposure to oxygen caused a portion of dangling radicals to be quenched, stopping the reaction and forming a dense network structure. The remaining dangling radicals could continue the polymerization, and more C=C bonds were converted than that in the continuing nitrogen atmosphere. This effect was not observed on using another photoinitiator, 1-hydroxycyclohexyl phenyl ketone (HCK), and diurethane dimethacrylate. The promotion of dark polymerization thus depends on the photoinitiator. Promotion of dark polymerization was observed in the case of OXE01 as it is less susceptible to the radical quenching of oxygen.

2-Mercaptopyridine and its analogues cause a tautomerization reaction between their thiol and thione isomers. The equilibrium state would be changed by the surrounding environment such as polarity. In this study, we have designed and synthesized a vinyl monomer having a 2-mercaptopyridyl moiety, and prepared a photoadhesive material including the monomer, 2-hydroxyethyl methacylate, and a photoradical initiator. Photoadhesion between various kinds of adherents was realized using this material with 6.0 J cm^-2 of UV irradiation at a wavelength of 365 nm, recording up to 8.8 MPa of shear strength. The effects and chemical states of 2-mercaptopyridyl moieties were examined by control and/or XPS spectral measurements. Interestingly, the adhesive strength increased gradually, indicating an autoxidation reaction between two 2-mercaptopyridyl moieties to form a disulfide bond and cross-linked polymer networks.

The degradation and recycling of polymeric materials are growing public interests recently, and the molecular design of degradable polymers is highly important. Herein the syntheses and photochemical behavior of photolabile polyphthalaldehydes (PPAs) with oxime ether terminals are reported. o-Phthalaldehyde (o-PA) was polymerized with 1 or 2-acetonaphthone oxime as initiators in the presence of DBU at low temperature and terminated with acetic anhydride. The incorporation of naphthyl oxime ether units and acetyl terminals was confirmed by NMR, UV, and IR spectral measurements. The repeating units of obtained PPAs were about 100. When PPAs were irradiated with UV light (>310 nm) in CHCl₃, peaks due to o-PA appeared. On irradiation of PPA films, peaks appeared around 1775 cm^-1 in IR spectra, suggesting the formation of phthalide which could be derived from photo-transformation of o-PA. These spectral changes clearly indicated the proceeding of photo-depolymerization of PPAs. In order to analyze the mechanical property changes of PPA films on irradiation, nanoindentation technique was attempted. It was found that reduced modulus of PPAs decreased on irradiation, which supported the photo-depolymerization as observed in spectral analyses.

We have developed photocrosslinked films containing a blend of dinaphthylfluorene having episulfide moieties and photobase generators by UV irradiation. The photogenerated amine from the photobase generators catalyzed the crosslinking reaction of the episulfide moieties. The photocrosslinking properties of the blends were significantly affected by the irradiation and baking conditions. We have successfully fabricated films with high refractive indices (1.714 at 589 nm) and a high thermal stability (5% weight loss temperature: 304 ℃).

Acrylate-based photosensitive resins for digital light processing (DLP) 3D printing generally suffer from large volumetric shrinkage, insufficient functionality conversion and heterogeneous networks. Based on thiol-ene click chemistry, we developed a series of thiol-ene-acrylate ternary formulations and systematically studied the effects of each composition on the photopolymerization kinetics and thermomechanical properties. The ternary systems exhibit very low viscosity (< 0.15 Pa·s) and sufficient thermal storage stability. The mechanical properties of the networks can be adjusted by simply altering the components ratio. With optimal parameters, the thiol-ene-acrylate ternary system can be applied to DLP 3D printing to fabricate delicate objects.

Macroscopic and precise alignment control of functional molecules can provide increased functionality and enhanced device performance. However, even the most powerful current method has some limitations, such as the need for polarized light and photoresponsive dye molecules. We reported an alignment process based on a new concept of scanning wave photopolymerization (SWaP) that achieves an arbitrary alignment pattern by spatiotemporal light-triggered molecular diffusion. Here, we investigate the effect of crosslinker on molecular alignment by SWaP. We found that the controlled concentration gradient of polymer added with the optimal amount of crosslinker improved the degree of alignment of the liquid-crystalline polymers. SWaP could be employed as a simple and versatile fabrication process for preparing highly functional materials and devices that require alignment control.

Bulk polytetrafluoroethylene (PTFE) can be modified via X-ray irradiation. The X-rays, which have a continuous spectrum from 3 to 8 keV, penetrate deep into the PTFE substrate and induce a scission in the polymer main chain, -C-C-. In previous research, the optical properties of a PTFE sample were successfully modified; UV and visible transmittance drastically increased in the irradiated area of the substrates. In this study, the characterization of the chemical structure of the samples was carried out using Raman and FTIR spectroscopies. The results suggest the formation of CF₃ branches, which are not intrinsic to PTFE. In previous works, it has been reported that a similar modification was achieved using electron beam irradiation of several-MeV in molten PTFE, or by α-irradiation onto a PTFE substrate, where the modification depth was of tens of micrometers. On the contrary, we have succeeded the similar modification by using the X-rays.

The oxidative polymerization of thymol was performed using a copper chloride(I) catalyst with a bulky 2-(p-tolyl)pyridine ligand in toluene under oxygen atmosphere; the reaction produced linear poly(thymol) (PPE_Th) with a number average molecular weight (M_n) and its distribution (M_w/M_n) of 43,000 and 1.6, respectively. The resulting polymer consists of an almost perfect C–O linkage with good solubility, such as in toluene, chloroform, tetrahydrofuran, and N-methylpyrrolidone, when the polymerization was conducted below 40 ℃. The resulting PPE_Th is an amorphous polymer with glass transition temperature (T_g) and 5 wt% loss temperature in nitrogen (T_d5) of 130 ℃ and 402 ℃, respectively. The transparent pale-yellow film was obtained by solvent casting method.

Aromatic polyimides PI-3e-PMDA and PI-3e-m (m = 0-4) with 3 ether linkages per monomer unit were prepared from bis[4-(4-aminophenoxy)phenyl] ether (1) and various tetracarboxylic dianhydrides, pyromellitic dianhydride (PMDA), 3,3’4,4’- biphenyltertacarboxylic dianhydride (DA-0), 3,3’’4,4’’-p-terphenyltertacarboxylic dianhydride (DA-1), 3,3’’’4,4’’’-p-quarterphenyltertacarboxylic dianhydride (DA-2), 3,3’’’’4,4’’’’-p-quinquephenyltertacarboxylic dianhydride (DA-3), and 3,3’’’’’4,4’’’’’-p-sexiphenyltertacarboxylic dianhydride (DA-4), by a conventional two-step procedure that included ring-opening polymerization in NMP and subsequent thermal cyclic dehydration. The polyimides were characterized by wide angle X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetry (TG), and dynamic mechanical analysis (DMA), and compared on the basis of the number (m) of phenylene units. PI-3e-PMDA and PI-3e-m (m = 0-4) had glass transition temperatures (Tg) at 280 ℃ and 210-230 ℃, respectively, and T_g values were not dependent on m. The storage modulus (E’) of PI-3e-m decreased at about 200 ℃, after which a rubbery plateau resion was seen, followed by a further decrease at about 330 ℃. The DMA results for the annealed PI-3e-PMDA and PI-3e-m (m = 0-4) were also compared and discussed on the basis of m.

Gas permeable mixed matrix membranes (MMMs) based on a polymer of intrinsic microporosity (PIM-1) was studied focusing on the effect of the expansion of nano-space formed by surface modification on non-porous silica nanoparticles on gas permeability. The silica nanoparticles modified with different generations dendritic moieties were successfully synthesized and characterized by FT-IR and TGA measurements. The CO₂ permeability of the MMMs significantly increased with an increase of loading of the particles and addition of the particles with high modification ratio was more effective in improving gas permeability. The expansion of nano-space formed by the surface modification on silica nanoparticles would improve gas diffusion coefficient in MMMs. This was supported by the correlation between the diffusion coefficient in the MMMs and the peaks observed by ¹²⁹Xe NMR spectroscopy.

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes have been investigated for the applications to all-solid-state lithium ion batteries. However, the lithium ion conductivities of the present electrolyte membranes are insufficient for practical applications. In our previous study, composite membranes composed of PEO-grafted polyimide (PI-g-PEO) nanofibers showed good electrolyte characteristics. In this study, a series of PI-g-PEO with various PEO lengths and grafting ratios were synthesized and converted to nanofibers. The nanofiber frameworks (NfFs) with high PEO weight fractions showed much higher ion conductivity than the corresponding membranes. The NfF composite membrane was fabricated by composing the best NfF and the PEO/Li matrix electrolyte. The NfF composite membrane showed high ion conductivity at low temperatures and good secondary battery performances.

Polyimide (PI) nanoparticles are known as precursors of non-precious metal cathode catalysts, which are expected to be the alternatives for platinum-based catalysts for the globalization of polymer electrolyte fuel cells. Our research group previously reported the synthesis of PI nanoparticles with diameters of approximately 60 nm by the precipitation polymerization of pyromellitic dianhydride and 1,3,5-tris(4-aminophenyl)benzene. This study focuses on the synthesis of PI nanoparticles with even smaller size by stabilizing the polymer/solvent interface. In addition to the same monomers as the previous study, dodecylamine was added to the polymerization system as an end-capping agent, and PI nanoparticles with diameters less than 50 nm have been successfully obtained.

We fabricated the pH-responsible polymer nano-film possessing carbamate groups, which were easily decomposed in acidic condition, in the linker moieties. In pH 7.4 phosphate buffer saline the number average diameter of pH-responsible polymer nano-film was about 350 nm and its size distribution had almost unchanged for 3 days. In pH 5.0 acetate buffer solution the scattering intensity of polymer nano-film in DLS measurement gradually decreased and it was difficult to measure the particle diameter of polymer nano-film after 15 h due to the lower scattering intensity. It was suggested that most of the polymer nano-film might be decomposed until 15 h.

Electrospray apparatus, using ionic liquid (1-ethyl-3-methylimidazolium acetate) as a counter electrode, was developed and investigated by the spray current measurement. The current–voltage characteristics were studied using conductive ionic liquid and non-conductive silicone oil. The capturing and neutralizing of ejected droplets on the ionic liquid counter electrode were confirmed by the spray current monitoring. In addition, the electrospray apparatus was evaluated using the empirical formula of current flow characteristics. The obtained exponent value of n_iq = 0.517 in the electrospray apparatus using the ionic liquid counter electrode was consistent with the exponent value n of ~0.5, which is reported by the standard electrospray set up using a metal counter electrode. The electrospray techniques using ionic liquid as a counter electrode may provide environmentally sustainable processes for the production and functionalization of nanoparticles.

A crystalline acrylic-type polymerizable monomer of Nalidixic acid (NA) was synthesized by linking NA molecule to acrylic acid (AA) via acid-anhydride conjugate. Then, the monomer was polymerized in solid state by vibratory mixing with plasma-irradiated lactose powders as postprocessing-free initiators. The characterization of the resulting polymeric prodrug powders by ESR, XRPD and FT-IR analysis confirmed their synthesis successfully. The in vitro hydrolysis study of the polymeric prodrugs was carried out in three different buffer solutions at 37 ℃. The results indicated that the acid-anhydride conjugate of the polymeric prodrugs was relatively stable to acid-catalyzed hydrolysis, and the NA release was in sustained manner with no burst and enhanced in basic media, in which ca. 4%, 35% and 80% of NA was released in 12 h at pH 1.2, pH 6.8 and pH 8.5, respectively. The obtained results suggested that the studied systems could be potential antibacterial polymeric prodrugs to minimize drug-stomach exposure and to use for colonic-targeting drug delivery formulation.

We investigated the formulations of acrylates containing a diene as an additive. The mixtures of acrylate monomers, photoinitiators, and an additive were placed in an aluminum pan. The samples were irradiated by a medium pressure mercury lamp without a filter or by a 365-nm light through a band-pass filter. The effect of the initiators, irradiation wavelength, atmosphere, and additive on the conversion of the acryl unit was investigated by photo-DSC measurements. We found that the additive, 1,3-bis[(3-methyl-2-buten-1-yl)oxy]propan-2-ol (DPNG), was the most effective additive for suppressed oxygen inhibition. In addition, the suppressed oxygen inhibition was observed even in thin films of acrylates containing DPNG by in-situ FT-IR measurements.

A microwrinkle surface made of UV-curable resin is known to reduce the regular reflection or glare of light because the wrinkle structure diffuses the incident light. However, the regular reflection cannot be reduced completely because the back side of the film or substrate reflects light as well. To achieve greater reduction in regular reflection, we developed a double-sided nanowrinkle film prepared on a water surface. A mixture of dipentaerythritol penta-/hexa-acrylate (DPHA), 1,6-bis(acryloyloxy)hexane, and 1-hydroxycyclohexyl phenyl ketone (HCK, photoinitiator) was spread on a water surface containing an inhibitor (Cupferron), and exposed to UV light. The photopolymerization reaction shrank the liquid film, and solidification occurred simultaneously in the core of the liquid film. However, the top and bottom interfaces contacted air and water, respectively, and the oxygen in air and the inhibitor in water retarded photopolymerization. The difference in photopolymerization rates results in a mismatch of shrinking speed between the core and each interface, and forms a double-sided wrinkle film. The size of the wrinkles within 0.7 μm of air interface was obtained by changing the concentration of DPHA. The double-sided wrinkle film reduced the regular reflection of laser light (λ = 520 nm) more than the single-sided nanowrinkle film.

Stent-like complicated cylindrical structures were made with pipes of stainless-steel SUS 304 using new lithography and wet chemical etching. In the new lithography, patterns on a flat reticle were printed on a pipe coated with a resist film by synchronously scanning the reticle linearly and rotating the pipe around the axis, and limiting the momentary exposure area on the top ridge of the pipe by placing an oblong slit on the reticle in parallel to the pipe axis. The patterned pipe was wetly etched in an aqueous solution of ferric chloride using the resist patterns as etching masks. Because the etching was progressed equally in all the directions from the resist pattern edges, masked parts under the resist patterns were also gradually etched from the pattern edges and undercut during the pipe was penetrated through the wall. Caused by the undercut, obtained mesh widths became narrower than the resist pattern widths. However, a stent-like mesh structure with widths of 108±12.4 (3σ) µm was decently fabricated by appropriately controlling the resist pattern width and the etching time. To attain higher accuracy in the future, cross section profiles of the mesh and relationship between resist pattern widths and mesh widths were discussed in detail.