Zongguang Wang

Preparation and properties of organo‐soluble polyimides based on 4,4′‐diamino‐3,3‐dimethyldiphenylmethane and conventional dianhydrides

4,4′-Diamino-3,3′-dimethyldiphenylmethane was used to prepare polyimides in an attempt to achieve good organo-solubility and light color. Polyimides based on this diamine and three conventional aromatic dianhydrides were prepared by solution polycondensation followed by chemical imidization. They possess good solubility in aprotonic polar organic solvents such as N-methyl 2-pyrrolidone, N,N-dimethyl acetamide, and m-cresol. Polyimide from 4,4′-diamino-3,3′-dimethyldiphenylmethane and diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride is even soluble in common solvents such as tetrahydrofuran and chloroform. Polyimides exhibit high transmittance at wavelengths above 400 nm. The glass transition temperature of polyimide from 4,4′-diamino-3,3′-dimethyldiphenylmethane and pyromellitic dianhydride is 370°C, while that from 4,4′-diamino-3,3′-dimethyldiphenylmethane and diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride is about 260°C. The initial thermal decomposition temperatures of these polyimides are 520–540°C.

Preparation and properties of high‐pretilt‐angle polyimides based on an alicyclic dianhydride and long alkyloxy side‐group‐containing diamines

A series of polyimides were prepared by a solution polycondensation reaction between 3-carboxylmethylcyclopentane-1,2,4-tricarboxylic dianhydride and 4-alkyloxybenzene-1,3-diamines in N-methyl-2-pyrrolidone and chemical imidization with triethylamine and acetic anhydride. These polyimides possess great organo-solubility, high optical transparency, and high pretilt angles. They are soluble not only in strong polar aprotic organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, m-cresol, and 1,4-butyrolactone but also in common low-boiling-point solvents such as chloroform and tetrahydrofuran, and some are even soluble in acetone. They exhibit high transparency at wavelengths greater than 320 nm. They can generate pretilt angles greater than 5°, and some can even achieve pretilt angles greater than 10°. The pretilt angle of a polyimide increases with the increasing length of the alkyloxy side group. The polyimides possess glass-transition temperatures between 180 and 230 °C and thermal decomposition temperatures (onset temperatures) of about 435 °C.

Synthesis and characterization of side-chain polyimides for second-order nonlinear optics via a post-azo-coupling reaction

A two-step, generally applicable synthetic approach for nonlinear optical (NLO) side-chain polyimides was developed. This included the preparation of a preimidized, organosoluble polyimide with benzene moiety pendant from main chains, followed by the covalent bonding of the NLO chromophores onto the polyimide backbone via a post-azo-coupling reaction. The degree of functionalization of polyimides was estimated by UV-VIS spectroscopy. The glass transition temperature (Tg) of a polyimide decreased by only 10–20°C after the functionalization, which was much smaller than the decrease in Tg when the chromophores were chemically bonded to the polyimide main chains through an ether linkage using a post-Mitsunobu condensation. The solubility and thermal stability of polyimides were also studied.

Liquid crystal alignment on periodic microstructure induced by single-beam 532 nm polarized laser illumination on poly(urethane-imide) film

Abstract After illumination by single-beam polarized pulse laser (532 nm) with energies below the ablation threshold energy, periodic microstructure was prepared on an azobenzene-containing poly(urethane-imide) (PUI) film surface. The reflective polarized IR results proved that the azobenzene group tended to be oriented perpendicular to the surface periodic microstructure. The illuminated PUI surface was used as the alignment layer of liquid crystal (LC) molecules. The experimental results indicated that the LC molecules tended to align closely along the surface microgrooves of the surface periodic microstructure. But the anchoring energy of LC molecules on the PUI film surface was smaller than that calculated based on the Berreman theory, which indicated that LC alignment on the laser-illuminated PUI film surface was controlled by the surface microgrooves and anisotropic orientation of the azobenzene group.

Study on the preparation and properties of copolyimides based on hexafluoroisopropylidene bis(3,4-phthalic anhydride) and 1,12-di(4-aminophenoxy)dodecane

Abstract Copolyimides were prepared from hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA), 1,12-di(4-aminophenoxy)dodecane and 4,4′-diaminodiphenylether through a solution co-polycondensation reaction followed by a chemical imidization reaction. It was observed that copolyimides prepared with any diamine molar ratio studied (1,12-di(4-aminophenoxy)dodecane/4,4′-diaminodiphenylether=7/3∽1/9) were soluble in polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol, tetrahydrofuran (THF) and chloroform, while the corresponding homopolyimides were insoluble. Wide angle X-ray diffraction (WAXD) results show a clear relationship between the crystallinity tendency and the solubility of polyimides. High crystallinity tendency leads to low organo-solubility. The glass transition temperature of a copolyimide was in good agreement with Fox’s equation for random copolymers. The long flexible chains in the backbone of copolyimides are the least thermally stable part.

Molecular orientation in laser-induced periodic microstructure on polyimide surface

The dichroism of the laser-induced periodic microstructure on a polyimide surface was studied with polarized reflectance infrared spectroscopy. The experimental results show that the polar C=O groups in the polyimide exhibit a greater tendency of orienting in the direction parallel to the microlines while the nonpolar C–C–C linkages between the two benzene rings in the diamine moiety tend to orient in a direction perpendicular to the nanolines. This result indicates that the polyimide molecule chains tend to orient in a direction perpendicular to the nanolines.

Investigation of dipole orientation in a side-chain second-order nonlinear optical poly(urethane-imide) by real-time variable temperature FT-IR spectroscopy

Abstract The orientation and relaxation of the second-order nonlinear optical (NLO) groups in a side-chain poly(urethane-imide) before and after the electric poling has been investigated with real-time variable temperature FT-IR spectroscopy by monitoring the symmetrical stretching vibration of the nitro group. In situ second harmonic generation (SHG) and ultraviolet-visible (UV–Vis) spectroscopy were also used to compare with the FT-IR results. The results obtained by these techniques are in good agreement with each other.

Side-chain second-order nonlinear optical poly(urethane-imide)/photosensitive polyimide blends with the improved dipole orientation stability by photo-crosslinking

Abstract A negative tone photosensitive polyimide (PSPI) was incorporated into a side-chain nonlinear optical poly(urethane-imide) (PUI) in an attempt to improve the dipole orientation stability of PUI. Upon UV irradiation after electric poling, the relaxation of the order parameter determined by the UV–Vis spectroscopy of the blend film was much suppressed, and the stability of dipole orientation was effectively improved. The improvement in the stability of dipole orientation results mainly from the photo-crosslinking of PSPI, which restricts the movement of the PUI molecular chains.

All-optical poling of a side-chain poly(urethane-imide) film and surface morphology studies

All-optical poling (AOP) of a new side-chain poly(urethane-imide) (PUI) film was experimentally investigated. Besides the investigation of the preparation conditions and seeding parameters (including intensities, relative phase between the seeding beams and sample temperature) of the AOP process in this system, the surface morphology of the polymer film after the AOP was also studied using atomic force microscopy. Much less surface defects were observed for the all-optical poled PUI films than the corona poled films.

Liquid Crystal Alignment on Polyimide Surface with Laser-induced Periodic Surface Microgroove

The alignment behavior of liquid crystal on polymer surface patterned by laser-induced periodic surface microgrooves was studied. The experimental results suggested that both the surface microgrooves and the orientation of surface polymer molecules played roles in determining liquid crystal alignment behavior. When the depth of the surface microgrooves was small, the anisotropic orientation of surface polymer molecules was the major factor in determining the direction of liquid crystal alignment. In contrast, when the depth of the surface microgrooves is sufficiently large, the microgroove effect will exceed the effect of molecular orientation. The transitional depth was about 12–14 nm.