To develop novel epoxy resins having both high adhesion and excellent heat resistance, radical copolymerizations of 4-vinyloxybutyl glycidyl ether (VBGE) or 2-(2-vinyloxyethoxy)ethyl glycidyl ether (VEEGE) with N-phenylmaleimide (NPMI), in addition to copolymerization of 2-vinyloxyethyl glycidyl ether (VEGE) with NPMI, which was reported in our previous study, were carried out. The effects of flexibility of the central chain unit of epoxy-containing vinyl ethers (VEs) on the thermal, mechanical, and adhesive properties of the obtained copolymers were investigated. These radical copolymerizations using AIBN as an initiator in benzene at 60 ̊C afforded copolymers having number-average molecular weights of 91,000 to 161,000 in high yield. 1H NMR analysis showed that the structure of the obtained copolymers consisted of VBGE unit or VEEGE unit and NPMI unit. The glass transition temperature (Tg) of the copolymers depended on the composition of the copolymers and decreased as the flexibility of the pendant moiety of VE units increased. The thermal decomposition temperature (Td) of the obtained copolymers was higher than 300 ̊C, indicating their high heat resistance. Tensile shear adhesion strength and tensile strength of the cured copolymers (epoxy content: 2.52~2.63 mmol/g) obtained by curing reaction with polyfunctional aromatic amines were measured. Tensile shear adhesion strength was 1.8 to 4.6 N/mm2 and tensile strength was 21 to 28 MPa, which was found to depend on the flexibility of the pendant moieties of the VE units in the copolymer.
A potentially effective method to prepare fibers of polymer gels with chemically crosslinked structure using ultraviolet (UV)-reactive electrospinning (UV-ES) is demonstrated. The UV-ES method makes sure the polymerization (i. e., gelation) proceeds simultaneously with the spinning process through employing an UV irradiator between the nozzle and the target (fiber collector). The fiber manufacturing via UV-ES succeeded for both polymer gels of poly(N, N-dimethylacrylamide) (G(DMAA)) and poly(DMAA-stearyl acrylate-dodecyl acrylate) (G(DMAA-SA-DA)). It is found that the viscosity of gel reactions influences the fiber diameter greatly. Higher viscosity generally tends to result in an increase in diameter of fibers regardless of the electric field intensity. Depending on the spinning conditions, G(DMAA) fibers with a diameter ranging 2 nm ~ 5.5 µm, and G(DMAA-SA-DA) fibers with a diameter ranging 30~100 µm are produced. The FTIR measurement for the resultant G(DMAA) and G(DMAA-SA-DA) fibers illustrates the polymerization essentially completed while spinning the fibers. This study highlights the potential possibilities of the UV-ES method in practical fiber-manufacturing applications for polymer gels.
In order to investigate the diffusion behavior of reducing agents into hair keratin fibers, crosssectional samples of virgin white human hair treated with thioglycolic acid (TG), thiolactic acid (TL), and Lcysteine (CYS), which have a carboxyl group in their molecule, were prepared. After the treatment, the crosssectioned hair samples were dyed with methylene blue and the cross-sectional intensity spectra were measured at a wavelength of 664 nm (λmax of methylene blue) with a microspectrophotometer. The three different diffusion patterns from the three reducing agents (TG, TL, and CYS) were obtained. The diffusion pattern of TL, which appeared as a sharp boundary line by using an optical microscope showed a combination of Fickian (TG) and Non-Fickian (CYS) types. Also, the diffusion pattern of thioglycerol (TGR), cysteamine hydrochloride, butyrolactonethiol, and glyceryl monothioglycolate, which don’t have any carboxyl group in their molecule showed Fickian type characteristics. In addition, it was found that the different alkali agents influenced the diffusion behavior of TGR and TG into virgin white human hair, and especially the waving efficiency of the waved hair treated with TGR. From these experiments, it has been concluded that the diffusion patterns of the reducing agents depended on the electrostatic interaction between the human hair and the reducing agents, and the chemical structure of the reducing agents.