Wen-Jang Kuo

Microstructural and morphological characteristics of PS–SiO2 nanocomposites

Abstract A series of organic–inorganic hybrid materials have been prepared by copolymerizing styrene and alkoxysilane-methacrylate via the sol–gel process. The alkoxysilane-containing copolymer precursors were synthesized by free-radical copolymerization of styrene with an alkoxysilane-containing monomer, methacrylic acid 3-(trimethoxysilyl)propyl ester (MAMSE), at several feeds. The copolymer precursors were then hydrolyzed and condensed to generate PS–SiO 2 hybrid sol–gel materials. The hybrid copolymers possess excellent optical transparency and a nanoscale microphase separation. The copolymer precursors and their hybrid copolymers were characterized by FT-IR spectra, 1 H NMR spectra, DSC, and TGA thermograms. Chemical structural effect on the morphology and thermal properties was investigated with SEM, mapping photographs, and high-resolution solid state 13 C and 29 Si NMR spectra. It was found that compatibility between copolymer and silica mainly comes from incorporating the polymer with silica covalently. Moreover, MAMSE could be hydrolyzed to methacrylic acid and ester-interchanged to silyl methacrylate during heat treatment. This also enhances the compatibility between the copolymer and silica. The thermal properties of the PS–SiO 2 hybrid copolymers are improved as silica content increase. However, the presence of silyl ester groups, which were formed during heat treatment, would reduce the thermal stability of the hybrid copolymers.

Novel phosphorus-containing dicyclopentadiene-modified phenolic resins for flame-retardancy applications

2-[4-(2-hydroxyphenyl)tricyclo[5.2.1.02,6]dec-8-yl]phenol (HPTCDP) were prepared from dicyclopentadiene (DCPD) and phenol via Friedel-Crafts alkylation. DCPD-containing phenolic resin (DPR) was also synthesized by incorporating the DCPD-containing monomer HPTCDP with formaldehyde. DPR was further modified by grafting the phosphate group. The phosphorylation was confirmed by a Fourier transform infrared, 31P-NMR spectroscopy, and an element analysis. The phosphorus content in the DPR could be successfully tailored to give values of 3.46 to 7.79 wt % by varying the feeding ratios of the phosphorus group. The thermal stabilities of the phosphorus-containing polymers were identified by differential scanning calorimeter and thermogravimetric analysis. The glass transition temperature values were decreased as the content of phosphorus increased. High char yield 39–47 wt % in thermogravimetric analysis evaluation and limiting oxygen index values of 27 to 34 were found for all the phosphorylated phenolic resins. Such properties make these polymers highly promising for flame-retardant applications.

Polymers for Electro‐Optical Modulation

Second‐order nonlinear optical (NLO) properties of polymeric materials have been attracting a lot of attention, especially for such potential applications as fast waveguides electrooptic (EO) modulation and frequency‐doubling devices. For these photonic applications, the performance of the NLO materials has to be optimized. This requires not only a fundamental knowledge of inter‐relationship between their chemical and NLO properties, but new technologies competitive or superior to existing ones as well. This review focuses on the synthesis of NLO polymers including chromophore design, and the comparison among comprehensive EO polymer systems. Moreover, characterization and device fabrication of electro‐optical polymer planar waveguides are also reported in this review.

Chemical modification of dicyclopentadiene-based epoxy resins to improve compatibility and thermal properties

A series of siloxane-containing epoxy resins was obtained by curing dicyclopentadiene-containing epoxy DG with the silicon-containing curing agents TS, DS, and AS. Curing behavior was studied using DSC, and the activation energies of the DG curing reaction with curing agents TA, DS, and AS were found to be 59, 80, and 157 KJ/mol. Meanwhile, the curing reaction of DG with diamines was found to be a first-order reaction using Arrhenius plots. In addition, thermal stability and the weight loss behavior of the cured polymers were studied via TGA. The silicon-containing resins displayed higher weight loss temperatures and higher char yields than the silicon-free resin. The activation energies of degradation ranged from 108 to 206 KJ/mol. The morphology of the cured pieces were investigated using SEM. The DG/TS and DG/DS are more compatible between the epoxy and the curing agents than DG/AS. The limited oxygen index (LOI) values of 31 to 34 for the DG-based resin confirmed the effectiveness of silicon-containing epoxy resins as flame retardants.

Synthesis and macroscopic second-order nonlinear optical properties of poly(ether imide)s containing a novel two-dimensional carbazole chromophore with nitro acceptors

Taking advantage of the multifunctional characteristics of carbazole along with rational molecular design, a two-dimensional carbazole chromophore with strong nitro acceptors was synthesized by a facile synthetic route. A first molecular hyperpolarizability of 163 × 10−30 esu was acquired through solvatochromic methods. By doping of the chromophores into an organosoluble poly(ether imide), a series of guest–host NLO polymers were acquired. A high doping level up to 20 wt% was obtained without observing aggregation of NLO chromophores. The compatibility between chromophore and poly(ether imide) was also investigated by SEM and extraction experiments. In terms of compatibility, the molecular weight distribution of the polymer plays an important role. The second harmonic coefficients (d33) for the NLO-active poly(ether imide)s range from 7 to 23 pm V−1 depending on the doping level. The effect of two-dimensional structure on the NLO temporal stability was investigated by tracing the second harmonic coefficient as a function of time. Moreover, the relaxation behavior of the NLO systems was further examined by dielectric analysis. Large rotational cone volumes give the two-dimensional chromophore excellent orientational stability when the temperature approaches the glass transition temperature observed from DEA.

Enhanced Temporal Stability of an NLO Polyurethane via a Two-Dimensional Chromophore

A new NLO active polyurethane (T g = 145°C) based on a two dimensional NLO chromophore has been investigated. Two ends of this lambda-shaped chromophore can be directly bound to the main chain of polyurethane. After poling, fast relaxation of the effective second harmonic (SH) coefficient was observed at temperatures higher than 122°C. Morcover, excellent temporal stability at 100°C was obtamed despite the operating temperature being very close to the last relaxation temperature. This is due to the fact that embedding the ligid lambda-shaped chromophores into the polymer backbone effectively restricts molecular motion at temperatures close to T g .

Preparation and characterization of all organic NLO sol-gel materials based on amino azobenzene dyes

A series or NLO active chromophores based an amino azobenzene dyes have been synthesized by diazotization reaction. All organic NLO-active materials were obtained by introducing the chromophores into (hydroxymethyl)-benzoguanamine (HMBG) systems by a sol-gel process. All the sol-gel materials exhibit excellent optical transparency. Morphology, thermal and optical preperties of these polymers have been characterized. These NLO-active polymers can be classified into reactive systems and guest-host systems. In the reactive systems, the chromophores were condensed with HMBG in the sol-gel process. In the guest-host systems, the nonreactive chromophores were simply doped into HMBG matrix. A second harmonic coefficient, d 33 , of 23.2 pm/V has been obtained. Moreover, a systematic investigation of variation of chromophore chemical structures on NLO properties, has been investigated. Covalent bonding effect between chromophore and benzoguanamine as well as steric effect are shown to greatly enhance the temporal stability for these NLO-active sol-gel systems.

Orderly Arranged NLO Materials Based on Chromophore-Containing Dendrons on Exfoliated Layered Templates

Three chromophore-containing dendrons were intercalated into montmorillonite layered silicates via an ion-exchange process. Enlarged d spacings ranging from 50 to 126 A were achieved for these novel organoclays. After the organoclays were blended with a polyimide, the steric bulkiness of the dendrons and the interaction between dendron and polyimide resulted in an ordered morphology. The orderly arranged nanocomposites were characterized by a UV-visible spectrophotometer, a variable-temperature infrared spectrometer, and electro-optical modulation. The dendrons in layered silicates were capable of undergoing a critical conformational change into an ordered structure, indicated by the drastic changes of interlayer distances at certain packing densities. Electro-optical coefficients increased sharply from 0 to 6 pm/V while the conformational change occurred. Furthermore, the addition of a polyimide capable of interaction-induced orientation was found to exert an enhancing effect on the degree of the noncentrosymmetric alignment.

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.

All Organic NLO Sol‐Gel Material Containing a One‐Dimensional Carbazole Chromophore

A NLO-active polymer has been developed via combining chromophoric photorefractive characteristics and film optical quality of melamine network. A carbazole-containing NLO-phore can be acquired via a facile synthetic route, namely Knoevenagel condensation. Guest-host prepolymer was obtained by doping the chromophores into benzoguanamine matrix. After poling and curing process, a NLO-active organic sol-gel material with large second-order nonlinearity and excellent optical quality film has been achieved. Thermal stability of the polymer was analyzed via DSC and TGA. UV-vis spectra and second harmonic generation measurement were utilized to characterize the linear and nonlinear optical properties. Reorientation dynamic stability was used to study temperature dependence of NLO signal. The d 33 and d 31 values for the polymer are 19 pm/V and 9 pm/V, respectively. Long-term NLO stability was investigated by measuring effective second harmonic (SH) coefficient as a function of time. The effective SH coefficient retained 47% of its original value and leveled off after 10 h of thermal ageing at 80°C.