We prepared a new polyphthalaldehyde (PPA) macromonomer by introducing a polymerizable methacryloyl group at the terminal of PPA main-chain. Resulting macromonomer was copolymerized with butyl acrylate to obtain pressure-sensitive adhesives (PSAs). We also compared the behavior of the copolymers with those of polymer blends of poly(butyl acrylate) and linear PPA polymers to clarify the role of polymerization. Higher peel strengths were observed for copolymers than those of corresponding polymer blends. As an increase in irradiation time, the strength generally decreased, although once increased for the copolymer films at the early stage. These results suggest that the introduction and the depolymerization of PPA side-chains caused drastic changes in adhesive properties.

Liquid-crystalline materials with precise molecular orientation patterns have attracted much attention due to their potential application to diffractive waveplates by utilizing their optical anisotropy. However, even by the most sophisticated photoalignment processes, the control of large-area molecular orientation patterns remains a challenge due to the need of a fine spatial control of polarization state of incident light or light interference. Recently, we have developed a photoalignment method based on a novel concept of scanning wave photopolymerization (SWaP) that enables us to control arbitrary two-dimensional orientation patterns without polarized light. Here, we demonstrate the fabrication of LC polymer films with a cycloidal molecular orientation over a large area by SWaP with a digital light processor, and investigate their unique optical property of the resultant film as a cycloidal diffractive waveplate. SWaP could be an excellent method to provide a new pathway for designing high-performance optical devices.

Stereolithography 3D printers mainly use acrylic or epoxy monomers, or a mixture of these monomers. High-definition and smooth modeling is possible; however, the product is vulnerable to impact. These products are generally photopolymerized by irradiation with light of a single wavelength to obtain a cured product. In this study, radical polymerization and cationic polymerization were polymerized stepwise using initiators with different absorption wavelengths for acrylic and epoxy monomers, and stepwise irradiation with the corresponding light. The impact resistance was compared between a product cured by irradiation with only a single wavelength and the cured product obtained by stepwise irradiation.

In the acrylic and epoxy monomers copolymerization system, a hybrid crosslinking agent (CLA) with an acrylic group and an epoxy group at both ends of one molecule was added to a resin and cured photochemically. The hybrid CLA formed a crosslinked network between acrylic and epoxy polymer chains. The effect of this hybrid CLA on the mechanical strength of the resin was investigated. The results indicated that excellent impact resistance, acrylic monomer conversion rate, and heat resistance were obtained by the addition of a certain amount of the hybrid CLA to the resin. Furthermore, changes to the structure of the central skeleton of the hybrid CLA resulted in changes to the mechanical properties of the cured resin. When the internal structure of the cured resin with the hybrid CLA was observed using scanning electron microscopy, the structural texture indicated the formation of an interpenetrating polymer network (IPN)-like structure. This IPN structure could have a role in the improvement of the mechanical strength of the cured polymer.

The polythiocyanurates with high molecular weights were successfully prepared by the phase-transfer catalyzed polycondensation of triazinedithiol with activated dibromides. These polymers were soluble in tetrahydrofuran (THF) and N-methyl-2-pyrrolidone (NMP), and readily afforded colorless and transparent cast films. The films of polythiocyanurates exhibited good thermal stabilities such as thermal decomposition temperatures of 320 ˚C in air. A relatively high glass transition temperatures of the polymers were in the range of 112-143 ˚C. The optical transmittance of the films was as high as 80% at 400 nm. The films exhibited high refractive index of 1.73 at d line, which is attributed to the triazine rings and sulfur atoms, and Abbe's number of around 18. Furthermore, the films showed the low birefringence of 0.0007-0.0022 at d-line. The obtained polymers are promising candidates for thermoplastic optical lens application.

Copolymers of polysilane and allyl methacrylate were prepared using the polysilane as a photoradical initiator. The polysilane block and allyl group were retained even after photopolymerization. The σ-conjugation of polysilane block in the copolymer allowed it to exhibit light absorption in the ultraviolet region. Subsequently, an ene-thiol reaction between the copolymer and mercapto-containing molecule was carried out by photocuring a thin film of the mixture. The photoreaction formed –CH–CH₂–S– bonding between the organic component and a silica component that was formed by photolysis of the polysilane block in the copolymer. Therefore, the polysilane-allyl methacrylate copolymer successfully provided a silicon-rich organic–inorganic hybrid material.

Photopolymerization is an environmentally-friendly, non-destructive, safe and solvent-free method. Moreover it guarantees low energy consumption. Therefore the photopolymerization is used in many scientific disciplines, including dentistry for production photocurable dental materials. In this work, the new photoinitiating systems based on camphoroquinone (CQ) and iodonium salts with tosyl anion for initiation of photopolymerization of the acrylates monomers bisphenol A - glycidyl methacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA) was studied. As a reference, camphorquinone (CQ) and ethyl 4-(dimethylamino)benzoate (EDB) photoinitiating system was used.

Triggered by the notable evolution of organic-inorganic metal halide perovskite solar cells (PSCs) with three-dimensional (3D) ABX₃ (A: organic/inorganic cation, B: metal cation, X: halogen anion) structures, Ruddlesden-Popper two-dimensional (2D) pseudo perovskites given by A_n+1B_nX_3n+1 (n = 1, 2, …) are also becoming a material of interest, as they exhibit improved stability against moisture and oxygen. Controlling the crystallographic orientation of these 2D layers plays a key role in the power conversion efficiency (PCE) of PSCs and their environmental tolerance. Here, we report the effect of top thermal annealing (TTA) on the PSC photoconductivity and performance, where TTA is a process that exposes heat from the top side (rather than the bottom (substrate) side in normal annealing) to form the perovskite layer after anti-solvent treatment. The anisotropic photoconductivity in the in-plane and out-of-plane directions was evaluated, which suggested a vertical gradient of 2D/3D phases with a 3D-rich component on the surface.

Semiconductor quantum dot (QD) sensitization is one of the most attractive structures to employ QDs for photovoltaic application. The function of QD sensitized solar cells (QDSSC) is controlled by the interfacial charge transfer dynamics. Here we employ transient absorption spectroscopy (TAS) to assess charge transfer dynamics at CdS QD/TiO₂ interface, and correlate their dynamics with their solar cell performance. An electron injection occurs from CdS QD conduction band to TiO₂ on ultrafast time scales, and the time constant decreases from ~10 ps to 1 ps, as the QD size decreases from 4 nm to 1.6 nm. Also, the charge recombination lifetime at the QD/TiO₂ interface increases, as the QD size increases. An absorbed photon to current conversion efficiency (APCE) of the QDSSC increases, as the QD size increases. Therefore, we conclude that the APCE of the CdS QDSSC is controlled by the interfacial charge recombination dynamics competing with dynamics of the hole transfer from the QD valence band to the reduced electrolyte. The optimum CdS QD size is close to or larger than 4 nm, as long as the light harvesting efficiency of the CdS QD sensitized film is sufficiently high.

In the 2-step method of CH₃NH₃PbI₃, the CH₃NH₃PbI₃ layer is converted using methylammonium iodide (MAI) after coating a PbI₂ layer. Although the use of dimethyl sulfoxide (DMSO) is reported to enhance the crystal quality of perovskite layer, we could not achieve the similar result. We studied the relationship between the layer properties of PbI₂ and the DMSO content in solvent. In addition, we checked the layer properties of perovskite layer and the photovoltaic performance of the cells with the above perovskite active layers. We found the immerse process of PbI₂ in 2-propanol influences the reconstruction of PbI₂ morphology and the diffusion process of MAI depends on the PbI₂ morphology.

Fine-tuning physical properties by structural modification is important for developing organic semiconducting materials. In this work, we designed and synthesized new electron-accepting compounds containing naphtho[1,2-c:7,8-c']bis([1,2,5]thiadiazole (vNTz) or naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole (NTz) groups as electron-accepting units; these units are structural isomers. The vNTz-based compounds have an arch-shaped molecular backbone with C_2v symmetry, whereas the NTz-based compound forms an S-shaped molecular backbone with C_2h symmetry. Property measurements showed unique behavior originating from the vNTz core. An organic solar cell comprising the vNTz-based compound and poly(3-hexylthiopehene) showed a power conversion efficiency of 2.06%. This result demonstrates the potential of vNTz as an electron-accepting unit in organic semiconducting materials.

Herein, we study hole transport properties in various conjugated conducting polymers blended with polystyrene (PS) as an insulating polymer. By analyzing macroscopic current density–voltage characteristics, we found that the mobility is improved for the conjugated conducting polymers diluted in the PS matrix that exhibit a redshift in absorption spectra. This is probably ascribed to more ordered polymer chains caused by the addition of PS. We believe that such a dilution of polymer chains would be versatile strategies to enhancing charge transport properties, which will offer a breakthrough towards highly efficient wearable optoelectronic devices based on the conjugated polymers.

Color stabilities of experimental composite resins based on Bis-EFMA (a novel bisphenol A [BPA]-free monomer system) with 3M ESPE FiltekTM Z250 (FZ) and experimental composite resins based on bisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) were compared. Bis-EFMA was synthesized via the reaction between 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene and 2-(methacryloyloxy)ethyl isocyanate. Experimental Bis-EFMA-, Bis-GMA-, and UMDA-based composites were prepared (20% of each of Bis-EFMA, Bis-GMA, UDMA, or triethylene glycol dimethacrylate (TEGDMA) and 60% glass filler). Eighty composite resin materials were produced (n=5). The initial color values of composites on the first day, first week, and after the first month after immersion into black tea, coffee, cola, and water solutions were measured using a spectrophotometer (VITA Easyshade® V; Zahnfabrik, Bad Säckingen, Germany) against a white background. UDMA- and Bis-EFMA-based composite resins exhibited significantly less ΔE and ΔL compared to Bis-GMA based composite resins (p < 0.05). No significant difference was found between FZ and other composites (p > 0.05). Tea and coffee caused significant changes in total color, light value, red–green, and blue–green coordinate values changes (ΔE, ΔL, Δa, and Δb, respectively) compared to water and cola (p < 0.05). At one month compared to one week and one day, ΔE, ΔL, Δa, and Δb were significantly different (p < 0.05). Bis-EFMA has the potential to be used in commercial dental composites as a substitute for Bis-GMA in terms of better color stability.

Four N-phenyl substituted carbazole oxime ester photoinitiators were synthesized and their structure-activity relationship were systematically investigated. These photoinitiators have a broad absorption in the range of 300-400 nm and the tail absorption extends above 400 nm. Under 405 nm LED light irradiation, the oxime esters undergo photodecarboxylation and generate active free radicals to induce polymerization of acrylates. The tert-butyl substituted aldehyde-oxime ester Ph-N-CZ-2 with terminal methyl group exhibit the best photoinitiation performance among the four N-substituted carbazole oxime esters.

Electrical and optical properties in reverse mode polymer stabilized liquid crystal (LC) cells have been investigated. We have proposed a light scattering model between LC domains with different domain sizes to describe low driving voltage. The LC reorientation in large and small domains was numerically investigated by fitting to the measured relative permittivity of the cell as a function of applied voltage. Transmittance considering the light scattering between two size LC domains was estimated in addition to the scattering due to a refractive index mismatching between LC and the polymer matrix. By fitting the theoretical curve to the experimental data, we found that the light scattering between LC domains was dominant for the low driving voltage of the reverse mode LC cell.

This in vivo research aimed to compare the biocompatibility of five different Universal adhesives (UAs) in short and long periods. 108 polyethylene tubes filled with five UAs [Group 1: All Bond Universal (ABU), Group 2: Prime Bond Elect Universal (PBU), Group 3: Single Bond Universal (SBU), Group 4: Clearfil Universal Bond Quick (CUB), Group 5: Futurabond U (FBU)] or Group 6: empty (control group)] were implanted into the dorsal connective tissue of 36 rats. Groups 1, 2 and 3 were implanted in 18 rats, the other groups Groups 4, 5 and 6 were implanted in 18 rats. Then, the rats were sacrificed after time intervals 7, 30 and 90 days (n=12). Biopsy samples were examined in terms of inflammatory reaction, necrosis, macrophage infiltrate, giant cell and fibrous capsule criteria. When the UAs groups and control group were compared on the 7th, 30th and 90th days, significant statistical differences were found only on the 7th day in terms of fibrous capsule and macrophage infiltrate (p<0.05). In addition, statistical significant differences were found upon within the control group in terms of inflammation, necrosis, giant cell, fibrous capsule and macrophage infiltrate criteria on the 7th, 30th and 90th days (p<0.05). The all UAs that we used in our study have showed good biocompatibility in the subcutaneous tissues of the rats, and we think that they could be used clinically with resin-based restorative materials in all restorative treatments including deep dentine caries restorations.