Optical properties of the thin films of poly(methylpentoxysilane) homopolymers and copolymers

The optical properties of the thin films of asymmetrically substituted polysilane homopolymers and copolymers were studied. A conformational change in the organopolysilanes having (pentoxy,methyl) or (hexyl,methyl) groups was observed by polarized UV spectrometry and a wide angle X-ray diffraction. The polysilanes and polysilane copolymers having hexyl and pentoxy side chains were crystallized to form oriented films along the direction of the mechanically oriented polytetrafluoroethylene (PTFE) films. The bathochromic shifts were observed for polysilane and the polysilane copolymer having pentoxy side chains when the film thickness was small (ca. <50 nm). The influence of the thickness of the films on the spectral change was significant when the substituent was a pentoxy group, however, not when it was a hexyl group.     

Synthesis and gas transport properties of new copolymer membranes with trimethylsilyl groups

Copolymers of 3-methacryloxypropyl tris(trimethylsiloxy) silane (SiMA) with methacrylate (MMA) and copolymers trimethylsilyl methyl methacrylate (TMSMMA) with vinyl acetate (VAc) were synthesized by radical polymerization. Membranes were cast from their solutions. Gas permeability, 10-1000 Barrer, of SiMA-MMA membranes was higher than that of TMSMMA-Vac membranes because of higher concentration of trimethylsilyl groups. Both apparent activation energies for gas permeability were very small compared to those of ordinary polymeric membranes. Poly(SiMA) is rubbery and poly(TMSMMA) is glassy at an ambient temperature. Copoly(SiMA-MMA) and copoly(TMSMMA-VAc) were shown to be random copolymers by the relationship between gas permeability coefficients and the molar ratio of each monomer. A series of copolymers in this investigation was shown to be a rare case of the polymer of which gas permeability increased in spite of the larger side chain, trimethylsilyl group, being introduced in the polymer chains.     

Synthesis of 2-imino-1,3-dithiolanes containing trimethylsilylethynylthiolato groups

An efficient, eco-friendly, and simple one-pot approach for the synthesis of 2-imino-1,3-dithiolanes via reaction of allyl chloride, primary amines, carbon disulfide, and I₂ under solvent-free conditions is presented. The obtained 5-iodomethyl-2-imino-1,3-dithiolanes were converted into silyl-protected terminal alkynyl sulfides substituted 2-imino-1,3-dithiolanes by treatment with lithium 2,2,2-tris(trimethylsilyl)ethanedithioate, produced by the reaction of tris(trimethylsilyl)methyllithium (TsiLi) with CS₂.     

Polyalkoxyphosphazenes by room-temperature polymerization of an electronegative phosphoranimine monomer

A new electronegative alkovyphosphazene monomer, tris(2,2-dinitropropoxy)-N-(trimethylsilyl)phosphoranimine, has been prepared. The anionic polymerization of this monomer occurs even at room temperature, in contrast to that of previous trialkoxy-N-(trimethylsilyl)phosphoranimines, which require elevated temperatures for efficient polymerization. The new polymerizations occur via catalysis by tetra-n-butylammonium fluoride or even by adventitious moisture.     

Tris(trimethylsilyl)methyl functionalized 4‐chloromethyl styrene polymers: Effects of side chain modification on polymer structure and glass transition temperature

4‐Chloromethyl styrene was copolymerized with various molar ratio of methyl methacrylate or ethyl methacrylate by solution free radical polymerization method, at 70 ± 1°C using α,α′‐azobis(isobutyronitrile) as an initiator. Then, very highly sterically hindered tris(trimethylsilyl)methyl substituent was covalently linked to the obtained copolymers with liberation of chlorine atoms. The structure of all polymers was characterized and confirmed by FT‐IR, ¹H and ¹³C NMR spectroscopy techniques. The average molecular weight and glass transition temperature of polymers were determined using gel permeation chromatograph and differential scanning calorimeter instruments, respectively. Study of differential scanning calorimetry analyses showed that chemical modification of 4‐chloromethyl styrene copolymers with tris(trimethylsilyl)methyl substituents leads to an increase in the rigidity and glass transition temperature of polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 633–639, 2006     

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

Since the methylenecyclopropane moiety is found in many biologically active natural substances, the synthesis of methylene‐ and alkylidenecyclopropanes remains a considerable challenge. In addition, an attractive feature is their surprising stability, accompanied by a high level of strain, conferring on them an otherwise unattainable chemical reactivity. The growing interest in the chemistry of these compounds has in its turn stimulated the development of alternative approaches to their skeleton, aimed at selectively introducing structural and chemical diversification. The three principal methods to synthesize these important compounds are based on the formation of the cyclopropane ring, the use of preformed cyclopropanes, and the use of preformed methylene‐ and alkylidenecyclopropanes. Abbreviations: Ac: acetyl; Ar: aryl; Bn: benzyl; Boc: tert‐butoxycarbonyl; Box: bisoxazoline; BTMSA: bis(trimethylsilyl)amide; Bu: butyl; Bz: benzoyl; C: cyclo; Cod: cyclooctadiene; Cp: cyclopentadienyl; Cy: cyclohexyl; Dba: (E,E)‐dibenzylideneacetone; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DCE: 1,2‐dichloroethane; de: diastereomeric excess; DEAD: diethyl azodicarboxylate; DMAc: N,N‐dimethylacetamide; DME: 1,2‐dimethoxyethane; DMF: dimethylformamide; DOSP: N‐p‐dodecylbenzenesulfonylprolinate; Dppb: 1,4‐bis(diphenyl)phosphinoborane; Dppe: bis(diphenylphosphino) ethene; E: electrophile; ee: enantiomeric excess; Et: ethyl; Hex: hexyl; L: ligand; LDA: lithium diisopropylamide; LG: leaving group; MCPBA: 3‐chloroperoxybenzoic acid; Me: methyl; MEM: methoxyethoxymethyl; MOM: methoxymethyl; Mp: morpholinyl; Ms: mesyl; Naph: naphthyl; NFSI: N‐fluorobenzenesulfonimide; Ns: nosyl; Nu: nucleophile; Pent: pentyl; Ph: phenyl; PMB: p‐methoxybenzoyl; Pr: propyl; Py: pyridyl; SEM: 2‐(trimethylsilyl)ethoxymethyl; TASF: tris(dimethylamino)sulfonium difluorotrimethyl silicate; TBAF: tetra‐n‐butylammonium fluoride; TBS: tert‐butyldimethylsilyl; TEA: triethylamine; Tedicyp: cis,cis,cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane; Tf: trifluoromethanesulfonyl; TFP: tris(2‐furyl)phosphine; THF: tetrahydrofuran; THP: tetrahydropyran; TMS: trimethylsilyl; Tol: tolyl; Ts: 4‐toluenesulfonyl (tosyl).     

Synthesis and characterization of poly(3‐hexylthiophene)–poly(3‐hexyloxythiophene) random copolymers with tunable band gap via Grignard metathesis polymerization

A series of 3‐substituted polythiophene copolymers having different side chain arrangements of hexyl and hexyloxy groups has been synthesized via the Grignard metathesis (GRIM) method and systematically studied. Despite differences in monomer reactivity ratios for the nickel‐catalyzed chain transfer polymerization, random sequences of hexyl‐ and hexyloxy‐substituted polythiophenes with different monomer compositions and adjustable band‐gap energies can be synthesized according to their respective comonomer feed ratio, as evidenced from NMR, UV, electrochemical measurements, and computational calculations. Structural characterization from X‐ray diffraction measurements reveals that the flexible hexyloxy side chains of the monomer significantly affect the crystallinity and molecular packing of the random copolymers. This study shows potential for synthesizing random copolymers with different monomer reactivities via the GRIM method for future optoelectronic applications. © 2014 Society of Chemical Industry     

Thioxanthone sensitized photodegradation of poly(alkyl methacrylate) films

The thioxanthone‐sensitized photodegradation of poly(alkyl methacrylate) films [alkyl = methyl, ethyl, butyl, and hexyl] was studied using near UV‐vis light. The photooxidation process continued even after the total consumption of the sensitizer, possibly due to the excitation of the ketyl groups formed during the first stages of the process. The rate of oxidation, as well as the formation of hydroxy, peroxy, and ketyl groups was faster for polymers with larger ester groups. The decrease of the molecular weight of the degradated polymers was also larger for the hexyl substituted polymer. The side‐chain size effect was attributed to the larger amount of secondary hydrogens available for abstraction by the triplet state of thioxanthone, present in the larger ester groups. The lower glass transition temperature of the hexyl substituted polymer allows a better diffusion of oxygen to the deeper layers of the films that also contributes to the faster photodegradation rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High Throughput Analysis of Chiral Compounds Using Capillary Electrochromatography (CEC) and CEC-Mass Spectrometry with Cellulose Based Stationary Phases

To fulfill the ever-growing demand for rapid chiral analysis, this research presents an approach for high throughput enantiomeric separations and sensitive detection of model chiral analytes using capillary electrochromatography (CEC) with UV and MS detection. This was achieved utilizing a short 7 cm CEC columns packed with cellulose tris (3,5-dimethyl-phenylcarbamate) (CDMPC) or sulfonated cellulose tris (3,5-dimethylphenylcarbamate) (CDMPC-SO₃) chiral stationary phases (CSPs) applying outlet side injections in CEC-UV. The separation performance was compared between CDMPC and CDMPC-SO₃ CSPs for rapid enantio-separation in CEC-UV mode. In addition, using a high sensitivity UV-flow cell in combination with outlet side injections, the S/N and hence the limit of detection of the chiral drug could be improved. The 7-cm packed column was also used with traditional inlet injections for CEC coupled to a low-cost single-quadrupole MS. While outlet side injection was not possible in CEC-MS due to instrumentation constraints, the combined use of a short 7 cm column packed with CDMPC-SO₃ CSP provided several fold higher throughput. Both CEC-UV and CEC-MS with short packed bed has the potential for a simple, sensitive and cost-effective method for enantiomeric drug profiling in biological samples.     

Synthesis and characterization of photo‐crosslinkable polyfluorene with acrylate side‐chains

A photo‐crosslinkable polymer, poly[2,7‐(9,9‐dioctylfluorene)‐co‐2,7‐(9‐hexyl‐9‐(2‐acrylate ethyl)‐9H‐fluorene)] (P3), was synthesized and the photo‐crosslinkable acrylate groups were introduced into the side‐chains of the polyfluorene derivative after its polymerization. This method avoids the possible crosslinkage of the crosslinkable groups on the monomers during polymerization in the traditional synthesis route by the polymerization of the monomers with the crosslinkable side‐chains. The soluble and processable polymer P3 could be crosslinked via the acrylate groups in its side‐chains upon exposure to UV light in nitrogen atmosphere. The crosslinking was confirmed by IR spectroscopy: the IR peak of C?C bond at 1635 cm^?1 decreased and that of the vinyl C? H bond at 742 cm^?1 disappeared after the UV exposure. The absorption spectra of P3 remain unchanged after crosslinking, but a longer wavelength emission at 517 nm appeared in the photoluminescent and electroluminescent spectra of the crosslinked P3, which could be attributed to the formation of keto defects during the photo crosslinking. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2336–2342, 2006     

Improved and Practical Synthesis of [2,4,5‐Tris(trimethylsilyl)‐ phenyl](phenyl)iodonium Triflate and Utilization as a 1,4‐Benzdiyne Synthon

An efficient and improved method for preparing [2,4,5‐tris(trimethylsilyl)phenyl](phenyl)iodonium triflate as a 1,4‐benzdiyne synthon was developed by using phenyiodonium diacetate/boron triflouride⋅diethyl etherate [PhI(OAc)₂/BF₃⋅OEt₂] reagent. The iodonium triflate generated 3,4‐bis(trimethylsilyl)benzyne quantitatively to give cycloadducts with tetraphenylcyclopentadienone, furan and anthracene in high yields. These cycloadducts bearing two trimethylsilyl groups were transformed into the corresponding aryne precursors, which underwent subsequent cycloaddition reactions to afford polycyclic aromatic compounds such as 1,4‐dihydro‐1,4‐epoxyanthracene, naphthotriazole, triptycene, and anthratriazole derivatives in good to high yields. The total reactions are formally considered as double cycloaddition reactions of 1,4‐benzdiyne. This practical and useful formal benzdiyne strategy is described.

     

Novel hybrid sol-gel coatings for corrosion protection of AZ31B magnesium alloy

This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol-gel coating approach.Hybrid organic-inorganic sols were synthesized by copolymerization of epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol-gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005 M NaCl solution for 2 weeks. The sol-gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg-O-P chemical bonds.The structure and the thickness of the sol-gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol-gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol-gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling.     

Magnetic Field Effect on Chemical Compositions of Magnetic Aerosol Particles Synthesized Photochemically from a Gaseous Mixture of Iron Pentacarbonyl and Trimethylsilyl Azide

Under intense UV light irradiation with an Nd:YAG laser at 355 nm, a gaseous mixture of iron pentacarbonyl (Fe(CO)₅) and trimethylsilyl azide (TMSAz) produced aerosol magnetic particles with diameters of 50–100 nm. Two photon absorption of TMSAz and Fe(CO)₅ took place efficiently to produce trimethylsilyl nitrene and iron carbonyls (Fe(CO) _n n = 1–4). In cases where a partial pressure of TMSAz was high, nucleation reactions of aerosol particles proceeded via chemical reactions between trimethylsilyl nitrene and two iron carbonyls, resulting in bridging between two iron carbonyls by silyl nitrene. In cases where a partial pressure of TMSAz was low, the nucleation reactions proceeded via chemical reactions between two iron carbonyls, resulting in the formation of di-iron carbonyls with bridging >C?O group. Both of these nucleation reactions took place concurrently during aerosol particle formation. From FT-IR spectral change of sedimentary particles produced under an external magnetic field of up to 5 T, it was found that application of an external magnetic field accelerated the latter chemical reaction to result in the appearance of bridging ν(>C?O) band in FT-IR spectrum of the magnetic particles.

Copyright 2013 American Association for Aerosol Research     

Enhanced conductance properties of UV laser/RTA annealed Al-doped ZnO thin films

Thin films comprising 0.5 mol% aluminum-doped zinc oxide (AZO) were prepared on glass substrates by a spin-coating method for transparent conducting oxide (TCO) applications. UV laser was selected for the annealing of AZO thin films, due to the well matched energy bandgap between UV laser and AZO films. After the rapid thermal annealing (RTA) process, post UV laser annealing was carried out by varying the scan speed of the laser beam, and the effects of laser annealing on the structural, morphological, electrical, and optical properties were analyzed. The results indicated that UV laser annealing based on various scan speeds affects the microstructure, sheet resistance, and optical transmittance of the AZO thin films, compared with those of the only RTA processed thin films. X-ray diffraction (XRD) analysis showed that all films that preferentially grew normally on the substrate had a (002) peak. The optical transmittance spectra of the laser/RTA annealed AZO thin films exhibited greater than 83% transmittance in the visible region. Also, the sheet resistance (1.61 kΩ/sq) indicated that optimized UV laser annealing after the RTA process improves film conductance.     

Optical‐limiting properties of poly(arylene ethynylenes) containing thiophene ring

Poly(arylene ethynylenes) containing thiophene ring were synthesized in good yield. In synthesis, pyridine was added to accelerate reaction owing to its phase transfer effect on CuI. The optical‐limiting properties of the prepared polymers were investigated with a Q‐switched Nd : YAG laser at 532 nm with 10‐ns pulse width. The experiments showed that the order of the optical‐limiting response of the polymers is poly(3‐hexyl‐2,5‐thienyleneethylene) (P3) > poly(2,5‐dihexyloxy‐1,4‐benzyleneethylene‐3‐hexyl‐2,5‐thienyleneethylene) (P2) > poly(9‐hexyl‐3,6‐carbazoleethylene‐3‐hexyl‐2,5‐thienyleneethylene) (P1). It can be understood well by the comparison of their conjugation length and D‐A structure. In addition, the results indicated that introducing the electron‐rich aromatic ring into the polymer backbone to enhance the D‐A structure would be an effective way to improve its optical‐limiting property. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 131–135, 2004     

Poly(p-phenylene) graft copolymers with polytetrahydrofuran/polystyrene side chains

1,4-Dibromo-2,5-bis(bromomethyl)benzene was used as a bifunctional initiator in cationic ring opening polymerization (CROP) of tetrahydrofuran. The resulting macromonomer, with a central 2,5-dibromobenzene ring, was reacted in combination with 2,5-dihexylbenzene-1,4-diboronic acid by a Suzuki coupling, in the presence of Pd(PPh₃)₄ as catalyst, leading to a poly(p-phenylene) (PPP) with alternating polytetrahydrofuran (PTHF) and hexyl side chains. A polystyrene (PSt) based macromonomer with a central benzene ring bearing cyclic boronic acid propanediol diester groups, synthesized by atom transfer radical polymerization (ATRP), was also used as partner for PTHF in the cross-coupling reaction. A PPP with alternating PSt and PTHF side chains was obtained. PTHF macromonomer was also homopolymerized by a Yamamoto reaction. The resulting PPPs have high solubility in common organic solvents at room temperature. The new polymers were characterized by GPC, ¹H NMR, ¹³C NMR, IR and UV analysis. Thermal behavior of the precursor PTHF macromonomer and the final polyphenylenes were investigated by TGA and DSC analyses and compared.     

Synthesis of isoelectronic polyazomethine and poly(arylene vinylene) by a palladium‐catalyzed Suzuki coupling method

Two fully conjugated copolymers containing 2,7‐(9,9‐dioctyl) fluorene and 3,6‐(N‐hexyl‐9H‐carbazole) disubstituted rings and arylene vinylene or azomethine units in the main chain were synthesized through a palladium‐catalyzed Suzuki coupling method of 2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐dioctyl fluorene with 1,4‐bis(6‐bromo‐N‐hexyl‐9H‐carbazole‐3‐yl vinyl) benzene or N,N‐bis(6‐bromo‐N‐hexyl‐9H‐carbazole‐3‐yl methylidene) 1,4‐phenylenediamine. Bisbromine arylene vinylene and arylenazomethine monomers were synthesized by condensation of 3‐formyl‐N‐hexyl‐6‐bromo carbazole with tetraethyl‐p‐xylylene diphosphonate or 1,4‐phenylenediamine. Copolymers were characterized by FTIR, ¹H‐NMR, DSC, UV‐visible and photoluminescence methods. Copyright © 2005 Society of Chemical Industry     

Preparation at the water–oil interface of Janus composite nanoparticles and their photoelectric properties

A series of Janus composite poly(3‐hexyl thiophene)‐b‐poly(3‐thiophenehexanethiol)–gold nanoparticles were synthesized by self‐assembly at the water–oil interface, and their photoelectric performance was investigated. The results show that the precise Janus composite nanostructure could be controlled by the adjustment of the reaction temperature and stirring time. The UV–visible measurement revealed that the absorption maximum had an appreciable redshift, and the photoluminescence (PL) spectra indicated that the PL intensity of poly(3‐hexyl thiophene)‐b‐poly[3‐(6‐thiolhexyl thiophene)] decreased upon the addition of gold nanoparticles. In addition, compared to a common composite of poly(3‐hexyl thiophene), the conductivity properties of the Janus composite nanostructure increased remarkably. Therefore, the Janus composite nanoparticles have the potential for applications in photovoltaic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45107.     

Modification of Nafion Membranes by Impregnation with Ionic Liquids

Nafion 117 membranes were impregnated with various imidazolium (1‐hexyl‐3‐methyl‐imidazolium/HMI, 1‐butyl‐3‐methyl‐imidazolium/BMI) and pyrrolidinium (1‐butyl‐1‐methyl‐pyrrolidinium/BMPyr) based ionic liquids bearing hydrophobic (tris(pentafluoroethyl)trifluorophosphate/FAP, bis(trifluoromethylsulfonyl)imide/BTSI, hexafluorophosphate/PF₆) and more hydrophilic (tetrafluoroborate/BF₄) anions. The modified membranes were characterized in terms of uptake behavior, washing out of the ionic liquids by water, swelling in humidified environment, thermal stability, mechanical properties, ion exchange capacity and ion conductivity. Upon this treatment, the ionic liquids' cations partially replace the protons of the sulfonic acid groups in Nafion. While the ionic liquids act as potent plasticizers in the polymer matrix, thermal stability of these systems remains unchanged and swelling by water of the dried ionomer membranes is reduced. Ion conductivities at 120 °C under dry conditions have been found to be up to 100 times higher than for dry Nafion 117. In particular, modification of Nafion by ionic liquids bearing the bulky hydrophobic FAP anion seems promising.     

Simultaneous construction of polymer backbone and side chains by terpolymerization. Synthesis of polyethers with the allyl side chains from dialdehydes, alkylene bis(trimethylsilyl) ethers, and allyltrimethylsilane

Polyethers with allyl side chains were synthesized by the simultaneous acid-catalyzed reaction of dialdehydes (1), alkylene bis(trimethylsilyl) ethers (2), and allyltrimethylsilane (3). The reactions of 1, 2 and 3 were carried out in the presence of 10 mol% of triphenylmethyl (trityl) perchlorate at −55°C to yield polyethers having allyl groups in the side chains. When the dialdehyde having the ester moieties as 1, ethylene bis(trimethylsilyl) ether and 1,4-bis(trimethylsiloxy)cyclohexane as 2 were used, high molecular weight polymers were obtained. In the polymerizations at ambient temperature, the polymer was precipitated during the reaction because of crosslinking between the aromatic rings via a trityl perchlorate assisted Friedel-Crafts reaction. The soluble polyether with the allyl side chains reacted with 1,2-ethanedithiol in the presence of a radical initiator in benzene at 60°C to yield a crosslinked polymer quantitatively within 1 h. This polymer synthesis is unusual in that it concurrently constructs both the polymer backbone and the functional side chains from three monomers.