Yu Sui

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.

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.

Identification of the alignment of azobenzene molecules induced by all-optical poling in polymer film

The alignment of azobenzene molecules in DR19-PUI film induced by all-optical poling is identified. When the writing beams of frequencies ω and 2ω are both linearly polarized with their polarization directions parallel to each other, azobenzene molecules tend to reorient to perpendicular direction (i.e. direction perpendicular to the polarization of writing beams). At the end of the writing process more molecules orient in perpendicular direction than those in parallel direction (i.e. direction parallel to the polarization of writing beams). The alignment of molecules in parallel or perpendicular direction is, respectively, characteristic of noncentrosymmetry or centrosymmetry. It is the alignment of molecules in parallel direction that results in the second-order nonlinearity in the poled film.

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.