Synthesis,characterization, and thermo‐optical properties of azobenzene polyurethane containing chiral units

An optically active levoazobenzene polyurethane (PU) was synthesized and was based on the chromophore 4‐(4′‐nitrophenylazo) phenylamine, the chiral reagent L (?)‐tartaric acid, and toluene diisocyanate. The chemical structure and thermal properties were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, and differential scanning calorimetry. The PU had high number‐ and weight‐average molecular weights up to 52 300, a large glass‐transition temperature of 235.7°C, and an optical rotation of ?18.06°, The optical parameters, including the refractive index (n) and thermo‐optic coefficient (dn/dT); the dielectric constant (?) and its variation with temperature; and the thermal volume expansion coefficient and its variation with temperature of PU were obtained. The dn/dT and ? values for the polymer were in the range ?4.1200 to 3.6257 × 10^?4 °C^?1 and 2.00 ± 0.11, respectively. The dn/dT values were one order of magnitude larger than those of inorganic glasses, such as zinc silicate glass (5.5 × 10^?6 °C^?1) and borosilicate glass (4.1 × 10^?6 °C^?1), and were larger than organic materials, such as polystyrene (?1.23 × 10^?4 °C^?1) and poly(methyl methacrylate) (?1.20 × 10^?4 °C^?1). The ? values were lower than that of alicyclic polyimide and semiaromatic polyimide. The obtained PU is expected to be useful for optical switching and optical waveguide areas. The conclusion has a little significance for the development of a new digital optical switch. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ionomeric polyurethanes of pyridinium type with side azobenzene groups

New polyurethane cationomers synthesized by a two‐step substitution postreaction of urethane hydrogen atoms with nitroazobenzene groups were studied. As a starting polymer, a polyurethane based on poly(tetramethylene oxide)diol, isophorone diisocyanate, and 2,6‐bis(hydroximethyl)pyridine was used. After a preliminary metalation of the above polymer with natrium hydride, by reaction of polyurethane N‐sodate with 4‐nitro‐4′(β–iodoethylurethane)azobenzene, chromophoric groups between 2.85 and 10.53 wt % could be incorporated instead of hydrogen. Such polymers partially functionalized with azobenzene and further quaternized with methyl iodide led to the formation of pyridinium polyurethane cationomers N‐modified with nitroazo groups. The photosensible properties of the azobenzene chromophore in a polymer solution and film state indicated important differences in their photoresponse. In the polymer solution, the trans–cis photoisomerization of the chromophore is accompanied by an irreversible photobleaching effect, while under the same UV irradiation conditions, the ionomeric films exhibited an enhanced photostability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1240–1247, 2002     

Synthesis and physical properties of liquid‐crystalline copolymers with azobenzene segments

To investigate the effects of photoisomerizable azobenzene segments on the liquid‐crystalline characteristics and thermal properties of polymers, a series of liquid‐crystalline homopolymers and copolymers with azobenzene segments was synthesized. The azobenzene contents of the copolymers were estimated with elemental analysis. The photoisomerization of the azobenzene derivatives was studied with ultraviolet–visible (UV–vis) spectroscopy. The UV–vis absorption of the copolymers was found to be parallel with the content of the azobenzene segments. UV irradiation was found to cause a decrease in the copolymer transmittance around 355 nm due to the photoinduced isomerization from entgegen (E) to zusammen (Z). The phase‐transition temperatures and molecular weights of the polymers were investigated with differential scanning calorimetry and gel permeation chromatography, respectively. The variation in the phase‐transition temperature of the homopolymers before and after UV (365 nm) irradiation was investigated. The bended Z structure was found to disturb the order of the orientation of liquid crystals and to lower the phase‐transition temperature. The appearance of the polymer film was changed from opaque to clear after sufficient UV irradiation. The image recording of the polymer films was achieved after UV irradiation through a mask with pictures. The stability and reliability of the Nematic‐Isotropic phase transition of the homopolymers was evaluated with repeated cycles of 365‐nm UV irradiation and heating at 130°C. After the recycle phase transition was repeated nine times, no significant decay in the response and transmittance could be found. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Synthesis and thermal properties of polythioether‐based liquid‐crystalline polymers containing azobenzene in the side chain

BACKGROUND: Owing to the unusual structural rearrangement of polychloromethylthiirane (PCMT) at room temperature, it has not been used as the main‐chain backbone of side‐chain liquid‐crystalline polymers (SLCPs). However, it has been observed that PCMT has a relatively stable and clear structure under special conditions. Therefore, we attempted to synthesize SLCPs using PCMT as main‐chain backbone and investigated their thermal behavior. RESULTS: New polymers, poly[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2,3‐epithiopropane], in which the number of methylene units in the alkyl group is 4, 5 or 6, were prepared by means of reactions of corresponding (4‐methoxyazobenzene‐4′‐oxy)alkylthiols with PCMT. The structures of these compounds were confirmed using elemental analysis and ¹H NMR spectroscopy. The substitution ratios of the copolymers with 4, 5 and 6 methylene units in the alkyl group were 56, 75 and 80%, respectively. Differential scanning calorimetry measurements and polarized optical microscopy observations showed that the resulting copolymers exhibited thermotropic liquid‐crystalline mesomorphism with nematic phase except for the copolymer with a 56% substitution ratio. The decomposition temperature of all the synthesized copolymers was near 195 °C. CONCLUSION: This investigation has demonstrated that PCMT polymerized for 8 h has the ability to act as a suitable main‐chain backbone for SLCPs. Moreover, SLCPs could be obtained only by the reaction of PCMT with thiolate salt containing mesogenic groups. The substitution ratios increased with increasing number of methylene groups in the spacer. Copyright © 2009 Society of Chemical Industry     

The physical properties of aqueous cationic–nonionic polyurethane with poly(ethylene glycol methyl ether) side chain and its blend with aqueous cationic polyurethane

The cationic–nonionic dispersing centers with different chain lengths of poly ethylene glycol methyl ether (N‐PDEA 750, N‐PDEA 2000) were prepared from N‐diethanol amine (NDEA), isophorone diisocyanate (IPDI), and poly(ethylene glycol methyl ether) (PEO M_w = 750 and 2000), whereas aqueous cationic–nonionic polyurethane (N‐PDEA PU) with different side chain lengths were prepared by N‐PDEA 750 (or N‐PDEA 2000), 4,4‐methylene bis(isocyantocyclohexane) (H₁₂MDI), polytetramethylene glycol (PTMG 2000), ethylene diamine (EDA), and glycolic acid (GA) as cationic–nonionic dispersing center, hard segment, soft segment, chain extender, and quarternizing agent, respectively. The thermal and mechanical properties of PU casting film were then discussed. We also used N‐methyldiethyolamine (N‐MDEA) without PEO as cationic dispersing center to synthesize aqueous cationic PU (N‐MDEA PU). The PU blends were blending N‐PDEA 750 PU and N‐MDEA PU by different weight ratios and the physical properties of casting films and coated fabric of PU and PU blends were investigated. Regarding the thermal properties, we have found out that the cationic–nonionic PU (N‐PDEA 750 PU, N‐PDEA 2000 PU) has lower T_gs, T_ms, T_mH, and ΔH_H than N‐MDEA PU, apart from ΔH_s. The N‐PDEA 2000 PU with longer side‐chain PEO has lower T_gs, higher T_ms and ΔHs than N‐PDEA 750 PU. As for mechanical property, N‐PDEA PU has lower tensile strength of casting film compared with N‐MDEA PU. Regarding the comparison of side chain length of PEO, N‐PDEA 2000 PU with longer side chain has higher tensile strength than N‐PDEA 750 PU with shorter side chain length. In addition, N‐PDEA 2000 PU group that shows hard property in stress–strain curve, whereas N‐PDEA 750 PU shows soft property. The tensile strength of PU blends decreases as the content of N‐PDEA 750 PU increases. When the low‐blend ratio of N‐PDEA 750 PU (e.g., 5%), the tensile strength of casting film only shows less influence that can improve the elongation effectively. In terms of coating‐treated fabrics, cationic–nonionic PU‐coated fabrics show lower waterproof capacity (WP) than those treated by cationic PU. However, the water vapor permeability (WVP) and antiyellowing of the N‐PDEA 750 PU coated fabrics are significantly better than the one treated by cationic polyurethane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2963–2974, 2006     

Poly(aryl ether ketone)s with bromomethyl groups: Synthesis and quaternary amination

A series of bromomethylated poly(arylene ether ketone)s (PAEKs) with different contents of bromine tethered to the benzyl groups were successfully synthesized and characterized in this work. For this purpose, poly(arylene ether ketone) with 3,3′,5,5′‐tetramethyl‐4,4′‐dihydroxybipheny moiety (PAEK‐TM) was prepared by the aromatic nucleophilic polycondensation, and then the PAEK‐TM has benzylic methyl groups that were converted to bromomethyl groups by a radical reaction using N‐bromosuccinimide. Then, the bromomethylbenzyl groups in the membrane was converted to quaternary ammonium moieties in TMPAEK‐NOH. ¹H‐NMR measurements were used to characterize and confirm the structures of the resulting PAEK‐x‐BrTM and TMPAEK‐NBr derivatives (x refers to the molar percentage of bromine introduced per repeating units). TGA analysis showed that PAEK‐x‐BrTM exhibited a very low‐decomposition temperature at about 200°C corresponding to the C Br bond cleavage. The hydroxide conductivity of TMPAEK‐NOH membrane was 8 mS cm⁻¹ at room temperature, while the water uptake of TMPAEK‐NOH membrane was 22.3% at 20°C and 32.6% at 60°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Incorporation of azobenzene chromophore into poly(amide‐imide)

Poly(amide‐imide)s (PAI) bearing azobenzene chromophore groups were prepared by allowing a hydroxyl‐containing azobenzene dye (Disperse Red 1) to react with and reactive‐terminated PAI with weight–average molecular weights ranging from ～ 1.2 to 2.0 × 10⁴ g/mol. Such PAI were prepared by the condensation of trimellitic anhydride (TMA) and 4,4′‐methylene diphenyl diisocyanate (MDI). The final polymers presented a deep red color, with an absorption maxima in N,N‐dimethylformamide (DMF) solution at 490 nm, close to the azobenzene reactant used (Disperse Red 1) and molecular weights slightly higher than the pristine polymer, showing that the azo chromophore incorporation reaction does not lead to side reactions. The azofunctionalized polymer presented a high T_g value (170°C) that could be increased by a thermal curing process to 240°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 841–847, 2007     

Synthesis and application of hyperbranched poly(urethane‐urea) finishing agent with amino groups

The isocyanate‐terminated linear polyurethane prepolymer (LPPU) was successfully synthesized via step‐by‐step polymerization, with isophorone disocyanate (IPDI) and polytetramethylene ether glycol (PTMG, M_n = 2000 g/mol) used as raw materials, dibutyltin dilaurate (DBTDL) as the catalyst, 1,4‐butanediol (BDO) as the chain extender and anhydrous ethanol (EtOH) as the blocking agent. Then the hyperbranched poly (urethane‐urea) (HBPU) containing amino groups was synthesized by grafting LPPU on amino‐terminated hyperbranched polymers (NH₂‐HBP). The molecular structure of LPPU and HBPU were characterized by means of FT‐IR and ¹H‐NMR. It was founded that LPPU and HBPU were successfully synthesized as anticipated. The thermal stability and crystalline morphology of LPPU and HBPU were characterized and analyzed by TG and XRD. Additionally, it was also found that, after addition of 10% HBPU, the water absorption rate, water vapor transmission rate, and water vapor permeability increased markedly by 162.02%, 400.00%, 260.00%, respectively. The tensile strength of membrane decreased by 24.57% and the elongation at break increased by 26.92%. Compared with the leather finished by commercial PU finishing agent, the leather finished by HBPU presented better properties. The water vapor permeability of the leather finished by increased by 13.0%, and the dry‐ and wet‐rub resistances and the physical and mechanical performances were excellent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44139.     

Synthesis and characterization of side‐chain liquid‐crystalline polyacrylates containing azobenzene moieties

Syntheses of novel liquid‐crystalline polymers containing azobenzene moieties were performed by a convenient route with an acrylate backbone. The azobenzenes were key intermediates of the monomers, and side‐chain liquid‐crystalline polymers were prepared, that is, poly[α‐{4‐[(4‐acetylphenyl)azo]phenoxy}alkyloxy]acrylates, for which the spacer length was 3 or 11 methylene units. In addition, poly[3‐{4‐[(3,5‐dimethylphenyl)azo]phenoxy}propyloxy]acrylate was prepared with a spacer length of 3 methylene units. The structures of the precursors, monomers, and polymers were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The polymers were obtained by conventional free‐radical polymerization with 2,2′‐azobisisobutyronitrile as an initiator. The phase‐transition temperatures of the polymers were studied with differential scanning calorimetry, and the phase structures were evaluated with a polarizing optical microscopy technique. The results showed that two of the monomers and their corresponding polymers exhibited nematic liquid‐crystalline behavior, and one of the monomers and its corresponding polymer showed smectic liquid‐crystalline behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2653–2661, 2002     

Photosensitive poly(urethane acylsemicarbazide)s with azobenzene chromophores in the main chain

Poly(urethane acylsemicarbazide)s were synthesized with a two‐step process: (1) the in situ generation of diisocyanate through the thermal decomposition of an azobenzene‐containing precursor diazide and a reaction with ester/ether polyols to form an isocyanate‐terminated prepolymer and (2) chain extension in N,N‐dimethylacetamide with aliphatic or aromatic dihydrazides. Films cast from N,N‐dimethylacetamide solutions were characterized with attenuated total reflection/Fourier transform infrared spectroscopy, and the thermal properties were studied with thermogravimetric analysis and differential scanning calorimetry. The effects of the hard‐segment content and chain extenders on the static and dynamic mechanical properties were investigated. The photoresponsive behavior of the polymers and the effects of variations in the chromophore concentration and chemical composition on the kinetics of photoisomerization were investigated with ultraviolet–visible spectroscopy, which revealed that the rates were independent of the chromophore concentration. The photomechanical behavior, assessed with creep‐recovery measurements, proved that the systems underwent photochemical isomerization upon irradiation with ultraviolet light. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 444–454, 2004     

Poly(arylazophosphonates): New Arylazophosphonate‐Containing Polyurethanes and Polyesters for Laser Ablation Structuring

In this article we report the preparation of new arylazophosphonate‐containing polymers, poly(arylazophosphonates), via polycondensation reactions of bifunctional hydroxy functionalized arylazophosphonate‐containing monomers with isocyanate or acid chloride comonomers. The polyurethanes and polyesters were characterized by common methods such as ¹H, ¹³C, ³¹P NMR, FTIR, UV/visible spectroscopy, DSC, and GPC measurements. In addition, a number of polymer structuring experiments (macro and micro experiments) by means of laser ablation with a XeCl excimer laser were performed. In macro experiments, pulse number and fluence were investigated systematically and their influence on the ablation depth was discovered. In micro experiments, structures of high quality were obtained which possess clear contours without any debris on the polymer surface. Structures in the sub micron range were created by applying a phase mask. These high quality results indicate that the poly(arylazophosphonates) are well suited materials for laser ablation structuring with XeCl excimer lasers (e.g. for microstructuring or microlithography).

SEM image of sub micro structures of polymer APU 5 generated in experiments using a phase mask (line width: 0.3–0.5 μm, trench width: 0.3–0.5 μm, fluence: 3 J/cm²).     

Synthesis and properties of sulfonated poly(siloxane imide)s bearing dimethyl siloxane oligomers for fuel cell applications

A series of sulfonated poly(siloxane imide)s (SPSIs) were synthesized from 4,4′‐ketone dinaphthalene 1,1′,8,8′‐tetracarboxylic dianhydride (KDNTDA), a dimethyl siloxane oligomer‐based diamine, and a sulfonated diamine. The reduced viscosities ranged from 1.0 to 3.5 dL/g at 35°C in the triethylamine (TEA) salt form. The SPSIs showed anisotropic membrane swelling with larger swelling in thickness than in plane. They displayed reasonably high proton conductivity, thermal stability and good mechanical properties. The KDNTDA‐based SPSIs showed good solubility in common aprotic solvents not only in TEA salt form but also in proton form. The ¹H‐NMR results indicated that the molar content of the dimethyl siloxane oligomer in the SPSIs was 50–80% of that in the feed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and thermal properties of randomly branched poly(butylene isophthalate) containing sodium sulfonate groups

Randomly branched poly(butylene isophthalate) samples containing sodium sulfonate groups were prepared from dimethyl isophthalate, 3,5‐bis(carbomethoxycarbonyl) benzene sulfonate, tris(hydroxyethyl) isocyanurate, and 1,4‐butanediol, according to the well‐known two‐stage polycondensation procedure. The polymers, containing various amounts of branching units and ionic groups, demonstrated to be soluble in the most common organic solvents, an evidence that gelation was not reached under the polymerization conditions adopted. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. The sulfonate as well as the branching units had only a limited effect on the thermal stability, which slightly decreased with respect to pure poly(butylene isophthalate). The analysis carried out using DSC technique showed that the T_m of the copolymers decreased with increasing counit content, differently from T_g, which, on the contrary, increased. Baur's equation was found to describe well the T_m‐composition data. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1374–1379, 2006     

Reaction study of water‐borne polyurethanes based on isophorone diisocyanate,dimethylol propionic acid,and poly(hexane neopentyl adipate glycol)

The reaction of isophorone diisocyanate (IPDI) with poly(hexane neopentyl adipate glycol) (HNA) and dimethylol propionic acid (DMPA) was researched through an analysis of the contents of the NCO groups of the prepolymers through which water‐borne polyurethanes (PUs) could be formed. The reaction activity of DMPA with IPDI was studied and compared to that of HNA on the basis of an investigation into the effects of the temperature and catalyst on the prepolymerization and the viscosity of the prepolymers. The results showed that the reaction of IPDI with DMPA was much slower than the reaction of HNA, and so DMPA was concluded to be a relatively inert nucleophilic reagent for attacking IPDI. A temperature of 80°C was suitable, with dibutyl tin dilaurate as a catalyst, for producing prepolymers from IPDI and mixtures of HNA and DMPA, whereas 60°C without catalysis was enough to complete the reaction of IPDI with HNA. This study may be helpful in understanding the prepolymerization of water‐borne PUs and in manufacturing them. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 161–164, 2004     

Influence of azobenzene units on imidization kinetic of novel poly(ester amic acid)s and polymers properties before and after cyclodehydration

In this article, the imidization reaction kinetic of novel poly(ester amic acid)s with azobenzene units as side groups was studied by dynamic experiments by means of differential scanning calorimetry. Polymers differ in the number of chromophore moieties in their repeating unit and position in which azobenzene group is attached to the polymer chain. The kinetic parameters of poly(ester amic acid)s conversion to poly(ester imide)s was compared with data calculated for parent polymer, that is, without azobenzene groups. For the first time to our knowledge, the imidization kinetic of polymers with side azobenzene groups was studied. Kinetic parameters, such as the activation energy and frequency factor were estimated with the by Ozawa model [(E(O) and A(O)), respectively] and Kissinger model [(E(K) and A(K), respectively]. The values of activation energy determined with both models were in the range 167.1–198.3 kJ/mol. The lowest activation energy of imidization reaction exhibited polymer in which azobenzene units were placed between amide linkages. Polymers were characterized by FTIR, ¹H‐NMR, X‐ray, and UV–vis methods. The glass transition temperature of resultant poly(ester imide)s was in the range of 217–237°C. The presence of chromophore units slightly decreased T_g and significantly improved their solubility and optical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

New multifunctional sulfonamide-containing azobenzene chromophores: Synthesis and photochromic properties

The work presents synthesis and characterization of novel sulfadimethoxine and sulfabenzamide azo derivatives as well as the kinetic study of their trans-cis-trans isomerization. Spectral properties and kinetic constants were determined for the chromophores dispersed in poly(methyl methacrylate-co-butyl methacrylate) deposited on glass substrates in form of transparent, thin films. The maximum absorption bands were observed within wavelength in range of 446-457 nm for N-disubstituted aminoazobenzene derivatives and 361-362 nm for phenolic chromophores. For the phenolic azo derivatives of sulfadimethoxine and sulfabenzamide the photoisomerization induced with UV light followed the first order kinetics, while for other compounds the process combined of two parallel reactions with different rate constants was observed. The rate constants of thermal relaxation in the dark were usually few times smaller than those determined for photoinduced trans-cis isomerization. The change of real part of refractive index upon illumination determined by ellipsometry was within the range of 0.0043-0.0138.     

Effects of crosslinking time and amount of sulfophthalic acid on properties of the sulfonated poly(vinyl alcohol) membrane

A proton‐exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) via a sulfonation. The sulfonation was carried out by using sulfophthalic acid (sPTA) as a sulfonating agent. The sulfonated PVA membranes, with a variety of degrees of substitutions, were obtained by varying the crosslinking time and the amount of sulfonating agents. The chemical structure and thermal stability of the sulfonated PVA were characterized by using FTIR and thermogravimetric analysis techniques, respectively. The ion‐exchange capacity (IEC) and water uptake of the sulfonated membranes was evaluated by titration and gravimetry techniques, respectively. It was found that the IEC of the membrane increased with the amount of sPTA. Water uptakes of the membranes could either decrease or remain unchanged with the crosslinking time, depending on the amount of the sulfonating agent used. Methanol permeability values of the membranes treated with 10% sPTA were relatively low, comparing with that of the Nafion 115 membrane. Proton conductivity values of the sulfonated PVA membranes ranged between 0.024 and 0.035 S/cm and they did not remarkably change with the crosslinking time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1931–1936, 2006     

Poly(propylene) composite with hybrid nanofiller: Dynamic properties

Mechanical, impact, and relaxation properties of in situ synthesized carbon nanotubes‐polyaniline (CNT‐PANi) hybrid nanoparticle‐filled poly(propylene) (PP) composites with or without an amphiphilic dispersing agent were investigated using tensile testing, notched Charpy impact testing, and dynamical mechanical testing methods. The reference material was MWCNT filled PP composite. Ethyl gallate (EG) was the dispersing agent which realizes high conductivity in PP composites with hybrid filler. Measured properties showed quite similar behavior of CNT‐PANi hybrid and neat CNT filled composites. Addition of 20% EG in PP did not cause essential differences compared to the neat PP. When the dispersing agent was added in filler containing PP composites, remarkable effects were observed, especially in PP‐hybrid composites. Mechanically, these materials had improved tensile properties, but they were brittle compared to the materials without dispersing agent. Dynamic mechanical analysis showed improvement in storage modulus, and in loss modulus the α transition was well observable. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of liquid crystalline networks doped with azobenzene molecules and their photochemical grating formation behavior

Liquid crystalline (LC) networks with macroscopically uniaxial molecular orientation were prepared by photopolymerization of mixtures of LC mono‐ and diacrylates and a donor–acceptor azobenzene compound in a homogeneous glass cell at the nematic phase, and their photoresponsive properties were investigated. The transparency of the LC networks decreased with a decrease in the crosslinking density with LC diacrylate. The LC networks crosslinked with a few mol percent of LC diacrylate showed an enantiotropic phase transition from an anisotropic phase to an isotropic phase as well as high transparency. Formation and removal of the grating were investigated by irradiating two writing beams with an argon ion laser. Grating less than 1.0 μm could be achieved, and the response time of formation and removal of the grating were in a range of a few tens of microseconds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 943–951, 2003     

Photocontrol of the refractive index of poly(methyl methacrylate) with a nitrone additive

Hydroxy‐substituted aromatic nitrone derivatives were used for the photochemical control of the refractive index of poly(methyl methacrylate) (PMMA) films. Upon irradiation with 366‐nm light in solution, these derivatives underwent rearrangement reactions, which eventually produced N,N‐diarylformamide derivatives in quantitative yields. Similar photoreactions of the aromatic nitrones in the PMMA films lowered the refractive index of the films by as much as 0.014. The magnitude of the observed refractive‐index change was enough for hydroxy‐substituted nitrones to be used as additives for the fabrication of graded‐index‐type polymer optical fibers. In addition, the refractive index of the PMMA films remained almost constant at any conversion of the starting nitrone derivatives for at least 70 days at room temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2517–2520, 2004