In order to overcome the defects of opacity, high gas permeability, poor heat and solvent oil resistance of methyl silicone rubber, optically transparent trifluoropropyl phenyl silicone rubber was prepared by introducing trifluoropropyl and phenyl to organic silicone molecules. Then organic polysilazane (OPSZ) was coated on the trifluoropropyl phenyl silicone rubber surface with tetramethylhexamethylenediamine as a catalyst and a dense coating with low gas permeability was achieved. This process realized low-temperature curing and siliceous transition. At the same time, optical performance, mechanical properties, oxygen permeation flux, and anti-sulfuration were measured. The results showed that the fluorine-containing phenyl silicone rubber had good optical transparency, tensile strength, elongation at break, tear strength, oil resistance and heat resistance. The OPSZ coating surface was continuous, uniform, dense and free of cracks and voids; meanwhile, the coating section was dense, uniform, seamless, without cracks. The interface between the coating and the silicone rubber exhibited good adhesion. Light transmission was over 92% between 400 and 800 nm. When the coating thickness was more than 12 μm, the oxygen permeation flux remained unchanged, lamps had good anti-sulfuration ability, and luminous flux was maintained at over 99.8%. when the mass fraction of tetramethyl hexamethylene diamine (w) was over 5%, siliceous transition was achieved under room temperature and 50% relative humidity for 24 h.

A series of polyester polyols were synthesized using 1,6-hexanediol (HDO), 1,4-cyclohexanedimethanol (1,4-CHDM) and trimethylol propane (TMP), alone or in combination with 1,4-cyclohexanedicarboxylic acid and adipic acid. The polyester polyols were reacted with isocyanate trimers to form polyurethane (PU) coatings. Physical properties of the polyesters such as hydroxyl value, acid value, molecular weight, viscosity, and glass transition temperature (Tg) had been determined, and the IR spectroscopic analyses of polyesters/PU were reported. The properties (impact resistance, film flexibility, hardness, optical transmittance, chemical resistance, water absorption, thermostability, and phase separation) of the PU coatings so prepared were characterized. The viscosities of polyester polyols were dependent on the structure of the alcohols. Polyester polyol containing only linear aliphatic diol (HDO) was a transparent liquid at room temperature. The viscosity was increased by raising the molar ratio of 1,4-CHDM and/or TMP. All PU coatings had excellent flexibility, impact resistance, and hardness. The coatings derived from diol CHDM had the highest hardness, and the PU derived from diol HDO had the lowest hardness. The chemical resistance and water absorption improved with greater molar ratios of 1,4-CHDM or TMP. Results of differential scanning calorimetry and wide-angle X-ray diffraction indicated that there was no obvious crystallinity in the PU networks. Dynamic mechanical analysis (DMA) results revealed that both CHDM and TMP can increase the Tg of PU, and the crosslinking density improved with increased molar ratio of TMP. Atomic force microscope (AFM) and DMA analysis revealed that the PU coatings had no obvious microphase separation, which enabled them to have excellent properties, and the different composition in polyols did not have significant influence on transmittance in the visible region. Results of thermogravimetric measurements indicated that all the PU coatings had good thermal stability.

A series of polyester polyols were synthesized by polycondensation reaction using adipic acid (AA), 1,4-cyclohexanedicarboxylic acid (1,4-CHDA), and 1,6-hexanediol (HDO), 1,4-cyclohexanedimethanol (1,4-CHDM) and trimethylol propane (TMP), in which the molar ratio of the reactants AA/1,4-CHDA was varied. These series of polyols were reacted with isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI), alone or in combination, to form polyurethane (PU) coatings.The physicochemical properties (chemical structure, hydroxyl value, acid value, and molecular weight) of the polyols so synthesized and the mechanical and optical properties (impact resistance, film flexibility, optical transmittance and phase separation) of the PU coatings so prepared were characterized with FTIR spectroscopy, wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and atomic force microscopy (AFM).The results of this study show that the AA/1,4-CHDA molar ratio, the isocyanate used, and the NCO/OH ratio all have a significant impact on the properties of the PU coatings. While AA/1,4-CHDA molar ratio does not seem to affect the film flexibility and optical transmittance of the PU coatings, it has a significant effect on the impact resistance of the coatings. Impact resistance of the PU coatings increases as the AA/1,4-CHDA molar ratio decreases (i.e. more 1,4-CHDA used). PU coatings based on IPDI and combination of IPDI and HDI exhibit higher impact resistance and optical transmittance than HDI-based coatings. While changing NCO/OH ratio has only a slight impact on the optical transmittance and little effect on film flexibility, impact resistance of the PU coatings first increase, then decline with an increase in NCO/OH ratio.Highlights► Synthesized a series of polyester polyols. ► Researched the effect of crystallization on the transparency of polyurethane. ► Studied the components of soft and hard segment on the properties of polyurethane. ► Investigated the water resistance and phase separation of polyurethane.

UV-curable polyurethane acrylates (UVPUA) were prepared, and Fourier transform infrared (FTIR) was used to monitor the synthesis process and cured films. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the microstructure of UVPUA films have also been studied. With soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segments decreases, and microphase separation of UVPUA becomes better. Soft segment crystallization appears with its molecular weight exceeding 2000, when its value reaches 4000, an even more obvious melting peak in differential scanning calorimetry (DSC) curve was observed. Congregation of hard segment domains and the improvement of phase separation were due to symmetry and regularity of isocyanate, while rigid benzene ring was beneficial to crystallize and increase the glass transition temperature (Tg). The increased crosslink density with increasing the function degree of diluent resulted in better phase separation, on the contrary, increasing the reactive diluent content led to the opposite because of a phase reversion. Microphase separation lower during quenching and annealing due to post-curing of 1,6-hexa-nediol diacrylate (HDDA) at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.

UV-curable polyurethane acrylates (UVPUA) were prepared, and Fourier transform infrared (FTIR) was used to monitor the synthesis process and cured films. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the microstructure of UVPUA films have also been studied. With soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segments decreases, and microphase separation of UVPUA becomes better. Soft segment crystallization appears with its molecular weight exceeding 2000, when its value reaches 4000, an even more obvious melting peak in differential scanning calorimetry (DSC) curve was observed. Congregation of hard segment domains and the improvement of phase separation were due to symmetry and regularity of isocyanate, while rigid benzene ring was beneficial to crystallize and increase the glass transition temperature (Tg). The increased crosslink density with increasing the function degree of diluent resulted in better phase separation, on the contrary, increasing the reactive diluent content led to the opposite because of a phase reversion. Microphase separation lower during quenching and annealing due to post-curing of 1,6-hexa-nediol diacrylate (HDDA) at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.