Triplet‐sensitized irradiation of a main‐chain liquid crystalline poly(aryl cinnamate) in three different phases

Visible light irradiation of thin films of a main‐chain liquid crystalline poly(aryl cinnamate) using ketocoumarins as triplet sensitizers leads to photochemical crosslinking and UV‐vis and FTIR spectroscopic changes associated with saturation of the cinnamate double bond, most likely by 2 + 2 photocycloaddition. The triplet sensitizers are themselves photolabile and are lost by photochemical reactions during the sensitization process. A new ketocoumarin sensitizer with decyloxy substituents and a reduced tendency to phase separate from the polymer is reported. A simple calculation of the sensitization stoichiometry shows that a single molecule of this ketocoumarin sensitizes the destruction of approximately 90 cinnamate chromophores in the “as cast” films below T_g and about 300 chromophores in the more‐ordered glassy nematic films and in “as cast” films of poly(vinyl cinnamate). Triplet sensitization of fluid nematic films leads, upon initial irradiation, to UV‐vis hyperchromism that is attributed to disruption of chromophore aggregation and, possibly, to disruption of the nematic mesophase as photoproducts begin to form. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 134–144, 2001     

Covalently attached self‐assembly of ultrathin films from hydroxy‐containing porphyrin and diazoresin

Ultrathin films from 5,10,15,20‐tetrakis(4‐hydroxyphenyl) porphyrin (HPP) and diazoresin (DR) via a H bonding interaction were fabricated with the self‐assembly technique. Under UV irradiation, the H bonds between the layers will convert to covalent bonds following the decomposition of the diazonium group of DR. The stability of the film against the polar solvent and electrolyte aqueous solution increases a lot because of the formation of the covalent crosslinking structure. Thus, the photoelectric conversion property of DR/HPP film can be measured directly with a normal photoelectric chemical cell with potassium chloride as the electrolyte. The maximum of the anodic photocurrent was measured as 1.7 μ Å for an eight bilayer DR/HPP film deposited on an indium–tin oxide glass electrode. The action spectrum of the photocurrent generation indicated that the HPP contained in the film is responsible for the generation of the observed photocurrent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3103–3108, 2003     

Preparation of a chemically amplified photosensitive polyimide based on norbornene‐end‐capped poly(amic acid ethoxymethylester)

A positive‐working chemically amplified photosensitive polyimide (PSPI) developable with basic aqueous solutions was obtained from poly(amic acid ethoxymethylester) (PAAE) as a polyimide precursor and diphenyliodonium 5‐hydroxynaphthalene‐1‐sulfonate (DINS) as a photoacid generator. The norbornene‐end‐capped PAAE based on 4,4′‐oxydiphthalic anhydride and 4,4′‐oxydianiline exhibited high transparency at 365 nm. The protection ratio of the ethoxymethyl groups was optimized to maximize the difference between the dissolution rates of the exposed and unexposed areas. The acid generated from DINS in the UV‐exposed region effectively deprotected the ethoxymethyl groups of PAAE by a chemical amplification mechanism. A 10‐μm‐thick film of the PSPI precursor system containing 16 wt % DINS exhibited a sensitivity (D^o) of 1100 mJ cm^?2 when developed with a 2.38 wt % aqueous tetramethyl ammonium hydroxide solution at room temperature. A fine, positive, 5‐μm line‐and‐space pattern was fabricated in a 15‐μm‐thick film with 1500 mJ cm^?2 of UV exposure. This resolution is excellent in comparison with those previously reported for chemically amplified PSPIs, and such a film can thus be used as a buffer coating in semiconductor packaging. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5520–5528, 2005     

Surface‐confined photopolymerization of single‐ and mixed‐monomer systems to tailor the wettability of poly(L‐lactide) film

The major objective of this research was to modify the surface characteristics of poly(L ‐lactide) (PLA) by grafting a combination of hydrophilic polymers to produce a continuum of hydrophilicity. The PLA film was solvent cast, and the film surfaces were activated by ultra violet (UV) irradiation. A single monomer or combination of two monomers, selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm), were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR‐FTIR spectroscopy and contact angle goniometry. Results showed that AAm dominated the hydrophilicity of the film surface when copolymerized with VAc or AA, while the water contact angles for PLA films grafted with poly(vinyl acetate‐co‐acrylic acid) varied more gradually with feed composition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6534‐6543, 2006     

Living cationic polymerization of a coumarin‐substituted vinyl ether and reversible photoinduced crosslinking of the resulting homopolymers and amphiphilic block copolymers

Living cationic polymerization of 4‐methyl‐7‐(2‐vinyloxyethoxy)coumarin (CMVE) was achieved using SnCl₄ in the presence of nBu₄NBr as an added salt at 0 °C. The number‐average molecular weight of the resulting polymers increased in direct proportion to the monomer conversion while retaining relatively low polydispersity. Structural analysis revealed that the resulting polymers carried pendant coumarinyl moieties. These coumarinyl moieties were crosslinked by irradiation with UV light at λ_max = 366 nm, and the crosslinked sites were then cleaved by irradiation with UV light at λ_max = 254 nm. The crosslinking behaviors of the polymers were studied by UV and FTIR spectroscopic measurement. PolyCMVE was soluble in dichloromethane but was found to be insoluble upon UV light irradiation. We also synthesized amphiphilic block polymers bearing coumarinyl moieties by living cationic copolymerization with an amphiphilic vinyl ether. The resulting block polymers were soluble in an aqueous medium and also formed micelle‐like aggregates. Upon UV irradiation of aqueous solutions above the critical micelle concentration, an efficient crosslinking reaction occurred. Photoinduced structural changes of these polymer aggregates in the solution state were further investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Modulating structural stability and acid sensitivity of photosensitive polymer micelles simply via one‐batch UV irradiation

This article describes the photosensitive polymer micelles whose structural stability and acid sensitivity can be widely tuned simply via one‐batch UV irradiation. To this end, the well‐defined poly(5‐ethyl‐5‐methacryloyloxy‐methyl‐2‐styryl‐[1,3]dioxane)‐block‐poly[poly(ethylene glycol) methacrylate] (PEMSD‐b‐PPEGMA) copolymers were synthesized via RAFT polymerization under mild visible light radiation at 30 °C. The results demonstrated that the irradiation of the homogeneous acetone solution with UV light only induced Z‐isomerization of their cinnamyl groups, while irradiating PEMSD chains in the bulky micellar cores only induced dimerization. Moreover, the micelles of previously Z‐isomerized copolymer could be effectively stabilized without changing their acid sensitivity on irradiating for shortly 3 min, while UV irradiation for 30 min could remarkably improve the acid stability of these micelles. These novel properties are of potential applications in controlled drug delivery. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and positive‐imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one‐pot polycondensation of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5‐diaminobenzoic acid (DABz) and bis[4‐(3‐aminophenoxy)phenyl]sulfone (m‐BAPS) in the presence of a γ‐valerolactone/pyridine catalyst system using N‐methyl‐2‐pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive‐tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10‐μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 934–946, 2001     

Synthesis of star‐shaped poly(n‐butyl acrylate) oligomers with coumarin end groups and their networks for a UV‐tunable viscoelastic material

Solvent‐free isothermal tuning of viscoelasticity of polymer materials is important for an emerging photochemical molding technology and photoreversible adhesives. In this study we designed a four‐armed star‐shaped poly(butyl acrylate, BA) oligomer having four coumarin end groups. The irradiation of UV at the wavelength of 365 nm (UV₃₆₅) to the viscous poly(BA) oligomer under a solvent‐free condition produced a solid network material along with the progress of dimerization reaction with coumarin end groups. The subsequent irradiation of UV at the wavelength of 254 nm (UV₂₅₄) caused dimer dissociation reaction to attain change in the mixing degree of star and network architectures in the material. Moreover, viscoelasticity of the network material was tunable by repetitive UV₃₆₅ and UV₂₅₄ irradiations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 9–15     

Design of photoresists with reduced environmental impact. II. Water‐soluble resists based on photocrosslinking of poly(2‐isopropenyl‐2‐oxazoline)

The performance of water‐ and solvent‐cast, two‐component photoresist films containing poly(2‐isopropenyl‐2‐oxazoline) or poly(2‐isopropenyl‐2‐oxazoline‐co‐styrene) with a photoacid generator has been investigated. These materials afford negative‐tone images after deep‐UV exposure and development in a suitable medium (water or toluene). Resist solutions prepared from polymers containing at least 80 mol % 2‐isopropenyl‐2‐oxazoline may be cast from and developed in pure water. Features of higher quality can be obtained when the resist is cast from 2‐methoxyethanol, probably because side reactions such as partial hydrolysis of the pendant oxazoline rings in aqueous environments are avoided. It was possible to resolve micrometer scale patterns using ca. 200 mJ/cm² of irradiation at 254 nm, followed by heating 2 min at 130°C and development in water alone. Image quality and etch resistance were improved using copolymers containing up to 20 mol % of styrene repeat units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1225–1236, 1999     

Molecular orientation of a ZnS‐nanocrystal‐modified M13 virus on a silicon substrate

The surface structure and cast film formation process of a ZnS‐nanocrystal‐modified M13 bacteriophage (ZnS–M13) were investigated. A ZnS–M13 film oriented under the influence of a capillary force was obtained on both single‐crystal and polycrystalline substrates. The film formation process was investigated with atomic force microscopy and scanning electron microscopy. The surface images showed that the degree of orientation of the molecular long axes greatly depended on the direction of force and the concentration of aqueous solutions. Controlling the aqueous solution concentration yielded a highly oriented ZnS–M13 film on an indium tin oxide plate. The ability to control the orientation of virus‐based films may lead to new types of hybrid materials in which the components are organized on several length scales. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 629–635, 2004     

Negative‐working photoresist based on a first‐generation dendrimer consisting of 4,4‐diphenylpentyloxy units

A first‐generation dendrimer ( 2 ), containing phenol groups in the exterior for solubilization in aqueous alkaline solutions, was evaluated as a new negative‐working, alkaline‐developable photoresist material. A negative‐working photoresist based on 2 , 4,4′‐methylenebis[2,6‐bis(hydroxymethyl)phenol] as a crosslinker, and diphenyliodonium 9,10‐dimethoxyanthracene‐2‐sulfonate as a photoacid generator was demonstrated. This resist gave a clear negative pattern through postbaking at 90 °C after exposure to UV light, which was followed by development with a 2.38% aqueous tetramethyl ammonium hydroxide solution at room temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1210–1215, 2005     

Photo‐induced association behavior of poly(sodium acrylate) bearing a small amount of malachite green

The photo‐induced association and dissociation of poly(sodium acrylate) containing a small amount of photoresponsive malachite green (MG) in aqueous solution were studied. It is known that MG dissociates into ion pairs under UV irradiation to produce the green triphenylmethyl cation. The cation thermally recombines with its counter anion to regenerate the colorless neutral compound. The random copolymer of acrylic acid with 0.05 mol % of MG monomer [P(A/MG0.05)] was soluble in aqueous 0.01 M NaCl at pH 12 as a unimer due to electrostatic repulsion between carboxylate pendent groups when the MG moieties were in the neutral form. On the other hand, these MG groups were converted to the cationic form on UV irradiation, leading to polymer aggregation driven by electrostatic interactions between the cationic MG and anionic carboxylate pendent groups. These aggregates could be dissociated by heating in the dark, as the cationic MG reverted to its neutral form, eliminating these attractive electrostatic interactions. The association and dissociation of the copolymer was monitored by dynamic light scattering (DLS). When the salt concentration in aqueous solutions of P(A/MG0.05) was increased from 0.01 to 0.5 M at pH 12, no aggregation was observed on UV irradiation because of ionic screening of the aforementioned electrostatic interactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Comb‐like polymers pendanted with elastin‐like peptides showing sharp and tunable thermoresponsiveness through dynamic covalent chemistry

Comb‐like polymers carrying two elastin‐like polypeptide (ELP) pendants in each repeat unit were synthesized. The densely attached peptide chains afford these polymers with sharp thermally induced phase transitions, and their lower critical solution temperature (LCST) can be varied with molecular weights, solution pH and salt concentrations. Through amino terminals in ELP pendants, oligoethylene glycol (OEG)‐based dendrons cored with aldehyde were attached to the polymers through dynamic covalent imines. By virtue of dynamic characteristics of these novel dendronized polymers, their LCSTs can be tuned significantly by dendron coverage to shift from that dominated by ELPs to that dominated by OEG dendrons. Furthermore, dendron coverage can be enhanced obviously by the thermally induced phase transitions or greatly by freezing the polymer aqueous solutions. The work provides a convenient methodology to improve thermoresponsiveness of ELPs through polymer topology and to switch their properties through dynamic covalent chemistry. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3379–3387     

Liquid crystalline dendrimers containing photoactive cinnamate units

Cinnamate‐containing dendrimers have been prepared by peripheral functionalization of the amine groups of a poly(propyleneimine) dendrimer with 4‐methoxycinnamate‐ or 4‐(N,N‐dimethylamino)cinnamate‐derived units and/or 4‐cyanobiphenyl units in different proportions. The synthesis, full characterization in solution, thermal properties and optical properties of the novel monomers, homodendrimers and codendrimers are reported. The composition of the molecular structure of the codendrimers has been elucidated by matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). These liquid crystalline dendrimers display lamellar SmA mesophases. The codendrimers have been tailored in such a way that the photoactive units and the liquid crystal units absorb in different regions in order to allow better control over the processes induced by light. Linearly polarized UV light irradiation studies performed on thin films of the cinnamate codendrimers show that they are photoresponsive. A photoinduced anisotropy is generated with increasing exposure time, but in‐plane amplification of anisotropy by thermal annealing in the mesophase was not observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A new oxidation state of aniline pentamer observed in water‐soluble electroactive oligoaniline‐chitosan polymer

A novel water‐soluble electroactive polymer, aniline pentamer crosslinked chitosan (Pentamer‐c‐Chi), was prepared by condensation polymerization of the terminal carboxyl groups in aniline pentamer with the amino side groups in chitosan in aqueous solution. The carboxyl groups were activated by N‐hydroxysuccinimide (NHS) and N,N′‐dicyclohexylcarbodiimide (DCC). The electrochemical behavior of anilinepentamer in this kind of crosslinked polymer was studied in acidic aqueous solution by means of cyclic voltammetry (CV), UV–vis, and electron spin resonance (ESR) spectroscopy. There were three reversible redox peaks in the CV of Pentamer‐c‐Chi. A new emeraldine oxidization state in the form of radical cations was proposed, which was associated with the new absorption band at 370 nm in the UV–vis spectra. The ESR of the aqueous solution of Pentamer‐c‐Chi showed a single Lorentzian shaped signal, which suggested the existence of radical cations. The new redox state was pH dependent and appeared only at pH < 3. The stability of radical cations could be attributed to the hydrogen bonds between radical cations, water, and chitosan. Morphological structure of the Pentamer‐c‐Chi can be adjusted by varying the content of aniline pentamer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1124–1135, 2008     

Synthesis,Characterization, and thermoresponsive properties of Helical Polypeptides Derivatized from Poly(γ−4‐(3‐chloropropoxycarbonyl)benzyl‐L‐glutamate)

A series of side‐chain‐functionalized α‐helical polypeptides, i.e., poly(γ‐4‐(3‐chloropropoxycarbonyl)benzyl‐_L‐glutamate) (6) have been prepared from n‐butylamine initiated ring‐opening polymerization (ROP) of γ‐4‐(3‐chloropropoxycarbonyl)benzyl‐_L‐glutamic acid‐based N‐carboxyanhydride. Polypeptides bearing oligo‐ethylene‐glycol (OEG) groups or 1‐butylimidazolium salts were prepared from 6 via copper‐mediated [2+3] alkyne‐azide 1,3‐dipolar cycloaddition or nuleophilic substitution, respectively. CD and FTIR analysis revealed that the polymers adopt α‐helical conformations both in solution and the solid state. Polymers bearing OEG (m = 3) side‐chains showed reversible LCST‐type phase transition behaviors in water while polymers bearing 1‐butylimidazolium and I^? counter‐anions exhibited reversible UCST‐type transitions in water. Variable‐temperature UV‐vis analysis revealed that the phase transition temperatures (T_pts) were dependent on the main‐chain length and polymeric concentration. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2469–2480     

Synthesis of photocrosslinkable hyperbranched polyesters and their film properties

Hyperbranched polyesters with terminal methacryloyl groups (HBPEAc) were synthesized by the one‐pot polyaddition of bisphenol A diglycidyl ether and trimesic acid in the presence of methacrylic acid with a number‐average molecular weights of 5100–7700 in 70–83% yields. The photoradical polymerization of HBPEAc was examined in the presence of 2‐methyl‐1‐[4‐(methylthio)phenyl]‐2‐morpholinopropan‐2‐one (Irgacure 907®) as a photoinitiator in the film state upon UV irradiation to afford the corresponding cured films quantitatively. The crosslinking densities of the cured films of HBPEAc were higher than those of the corresponding linear ones, and birefringence cannot be detected for the cured films of HBPEAc because of their random structures. Furthermore, an alkaline‐developable hyperbranched polyester containing pendant carboxyl groups (HBPEAc‐COOH) was prepared by the addition reaction of HBPEAc with cis‐1,2,3,6‐tetrahydrophthalic anhydride, and its patterning properties were examined to give the resolution of a 55‐μm‐line and 275‐μm‐space pattern by UV irradiation with 700 mJ/cm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4642–4653, 2005     

Predicting the solution morphology of a sulfonated pentablock copolymer in binary solvent mixtures

The solution morphologies of a midblock-sulfonated pentablock copolymer in miscible polar/nonpolar solvent blends were characterized as a function of solvent composition and polymer concentration using small angle X-ray scattering. Three distinct solution morphologies are observed upon changing the composition of the solvent blend. At low weight fractions of polar solvent, spherical, sulfonated-core micelles are observed, while spherical, sulfonated-corona (inverted) micelles are observed at high weight fractions of polar solvent. Polymer solution scattering is observed at intermediate concentrations of polar solvent. Additionally, the characteristic dimensions of the sulfonated-core micelles were found to change strongly upon variation of the solvent blend composition, indicating that these solutions—and correspondingly the morphology and properties of polymer membranes into which they are cast—can be tuned through simple variations in the solvent blend chemistry. We demonstrate that the solution morphologies and the characteristic micelle dimensions of these complex pentablock copolymer/binary solvent blends can be reliably predicted by considering the relative interactions of each polymer block and the solvent blend using the Hansen solubility parameters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 254–262     

A novel generation of photoactive comb‐shaped polyamides for the photoalignment of liquid crystals

A new approach to the synthesis of photoactive comb‐shaped homo‐ and copolyamides containing azobenzene, cinnamate, and coumarin side groups for photoalignment of liquid crystals was elaborated. Photooptical properties and photoorientational ability of these polymers with respect to liquid crystals were studied. It was shown that polarized UV irradiation of all spin‐coated polyamides leads to orientation of liquid crystalline molecules deposited on the polyamide thin films. The synthesized polymers containing cinnamate and coumarin side groups as well as azobenzene‐containing cyano‐ and nitro‐substituted polymers demonstrated good orientation ability in relation to liquid crystals displaying photoinduced planar orientation with high dichroism values within the range of 0.68–0.72. Contrary to the above‐mentioned polyamides, azobenzene‐containing fluorosubstituted polymers induced a homeotropic orientation of liquid crystals. It was shown that the synthesized photoactive polyamides can be considered as promising photoalignment materials for application in display technology, photonics, and other “smart” optical devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4031–4041     

Phase equilibrium studies on rod/solvent and rod/coil/solvent systems containing poly(α, L‐glutamate) having oligo(ethylene glycol) side chains

Phase equilibrium studies for semiconcentrated solutions of rodlike poly(γ‐benzyl L ‐glutamate) having oligo(ethylene glycol) as side chains (PBLG‐g‐OEG) have been investigated. The phase‐boundary concentrations in isotropic and anisotropic phases for N,N‐dimethylformamide (DMF) solution of PBLG‐g‐OEG with short side chains (PBLG2‐g‐380) are higher than those for solution of PBLG‐g‐OEG with long side chains (PBLG2‐g‐770). The lattice theory and the scaled particle theory for nematic solution, which don't distinguish the molecular architecture of the rodlike polymer, cannot explain this experimental result. Repulsive interaction between rodlike polymers by means of the attached side chains is proposed for the molecular orientation of PBLG‐g‐OEG in anisotropic state in order to describe the experimental result. Ternary phase diagrams of PBLG‐g‐OEG/poly(ethylene glycol) (PEG)/DMF show that the miscibility of rodlike PBLG‐g‐OEG and coiled PEG is most enhanced in the system of PBLG2‐g‐770, which has longest and largest amount of side chains. This experimental observation is explained by using the calculation based on the lattice theory and the repulsive interaction of side chains proposed above. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1331–1340, 2000