Thickness‐dependent swelling of molecular layer‐by‐layer polyamide nanomembranes

The thickness‐dependent water vapor swelling of molecular layer‐by‐layer polyamide films is studied via specular X‐ray reflectivity. The maximum swelling ratio of these ultrathin films scale inversely with thickness but more importantly show a dual‐mode sorption behavior characterized by Langmuir‐like sorption at low relative humidity and network swelling at high relative humidity. The thickness‐dependent network parameters are extracted using a proposed model that builds on Painter‐Shenoy network swelling model while taking into account the glass‐like characteristic below a critical swelling ratio, which also scales inversely with thickness. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 412–417     

Synthesis and thermal crosslinking of oxazolidine‐functionalized polyurethanes

A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (M_w ～ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007     

Crosslinkable poly(p‐phenylenevinylene) derivative

To simplify the fabrication of multilayer light‐emitting diodes, we prepared a p‐phenylenevinylene‐based polymer capped with crosslinkable styrene through a Wittig reaction. Insoluble poly(p‐phenylenevinylene) derivative (PPVD) films were prepared by a thermal treatment. The photoluminescence and ultraviolet–visible (UV–vis) absorbance of crosslinked films and noncrosslinked films were studied. We also studied the solvent resistance of crosslinked PPV films with UV–vis absorption spectra and atomic force microscopy. Double‐layer devices using crosslinked PPVD as an emitting layer, 2‐(4‐tert‐butylphenyl)‐5‐phenyl‐1,3,4‐oxadiazole (PBD) in poly(methyl methacrylate) as an electron‐transporting layer, and calcium as a cathode were fabricated. A maximum luminance efficiency of 0.70 cd/A and a maximum brightness of 740 cd/m² at 16 V were demonstrated. A 12‐fold improvement in the luminance efficiency with respect to that of single‐layer devices was realized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2124–2129, 2004     

Multiple levels hydrophobic modification of polymeric substrates by UV‐grafting polymerization with TFEMA as monomer

The hydrophobic solid surface modification with fluorine‐containing monomers has received tremendous attention because of its unique structure and excellent property. However, these hydrophobic films normally suffer from two major problems: one is weak interface interaction between fluoropolymers and substrates, and the other is the high cost of fluorine‐containing monomers. Herein, with the aim of feasible industrial application, a facile in situ UV photo‐grafting method is reported, which could ensure the formation of chemical bonds between fluoropolymer‐grafted layer and substrate with a low cost commercial 2,2,2‐trifluoroethyl methacrylate (TFEMA) as monomer. With low‐density polyethylene (LDPE) film as a model substrate, four kinds of poly‐TFEMA‐grafted layer are fabricated on LDPE films with different surface morphologies: polymer brush, polymer network, crosslinked nanoparticles, and a micro‐ and nanoscale hierarchical structure. The experimental results showed that the water contact angles (CAs) of the LDPE films grafted with polymer brush, polymer network, and crosslinked nanoparticles were (103 ± 2)°, (95 ± 2)°, and (122 ± 2)°, respectively, which were much higher than that of LDPE film. The introduction of micro‐ and nanoscale hierarchical structures can dramatically improve the surface roughness, which will further enhance the film hydrophobicity, and the water CA can reach as high as (140 ± 1)°. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1059–1067     

Photoreactive main‐chain liquid‐crystalline polyesters: Synthesis,characterization, and photochemistry

Three series of semiflexible and rigid main‐chain polyesters containing photoreactive mesogenic units derived from p‐phenylenediacrylic acid (PDA) and cinnamic acid have been synthesized by high‐temperature polycondensation. The thermal and mesomorphic properties of the polymers have been determined. The photochemical behavior of polymer P‐[1]‐T, which contains a PDA unit, has been studied both in solution and in films. In solution, [2+2] photocycloaddition, E/Z photoisomerization, and photo‐Fries rearrangement can take place. In contrast, the dominant process in spin‐coated films is the [2+2] photocycloaddition reaction, which causes crosslinking of the polymer. In films, the photochemistry and induction of anisotropy are strongly influenced by the aggregation of the PDA phenylester unit. A dichroism of about 0.2 has been induced in films by irradiation with linearly polarized UV light, and thus the capability of these films to induce optical anisotropy and align liquid crystals has been demonstrated. Liquid‐crystalline cells have been made with polarized irradiated films of P‐[1]‐T as aligning layers. A commercial liquid‐crystalline mixture has been used for this study, and a similar liquid‐crystalline order determined by polarized Fourier transform infrared to a commercial cell with rubbed polyimide as an aligning layer has been detected. Because of crosslinking of the irradiated P‐[1]‐T photoaligning layer, the photoinduced anisotropy is stable at high temperatures, and the liquid‐crystalline molecules are insoluble in the irradiated polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4907–4921, 2005     

Functionalization of surface‐grafted polymethylhydrosiloxane thin films with alkyl side chains

Thin films of crosslinked polymethylhydrosiloxane (PMHS) have been grafted on silica using the sol–gel process allowing further functionalization by effective quantitative hydrosilylation of SiH groups by olefins within the network. Postfunctionalization gives the polysiloxane network with n‐alkyl side chains. The PMHS coating was prepared by room temperature polycondensation of a mixture of methyldiethoxysilane HSiMe(OEt)₂ monomer and triethoxysilane HSi(OEt)₃ (TH) as crosslinker. The surface‐attached films are chemically stable and covalently bonded to the silica surface. Subsequently, films were functionalized without delamination. We showed by FTIR spectroscopy how the crosslinking ratio and the molecular size of the alkenes precursors influence the extent of the hydrosilylation reaction of SiH groups in the PMHS network. We have determined that quasi‐full olefin addition catalyzed by a platinum complex occurred within soft networks of less than 5% TH with 1‐alkenes CH₂?CH(CH₂)_n‐2CH₃ of various alkyl chain lengths (n = 5, 11, 17). Powders of PMHS gel were also modified with 1‐alkenes by hydrosilylation. The SiH groups within the soft gel (5% crosslinked) were fully functionalized as shown by ²⁹Si and ¹H solid‐state NMR. The structure of functionalized polysiloxane with n‐octadecyl and n‐dodecyl side chains was studied by FTIR, wide angle X‐ray diffraction, and DSC showing crystallization of the long n‐alkyl chains in the network. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3546–3562, 2008     

New photo‐induced thiol‐ene crosslinked films based on linear methacrylate copolymer polythiols

Thiol‐ene radical addition by photolysis is a highly efficient click reaction of sufhydryl groups with reactive enes that has been extensively explored as a promising means to construct multifunctional materials. Here, photo‐induced thiol‐ene crosslinked films composed of linear methacrylate copolymer polythiols (MCPsh) are reported. Well‐defined MCPsh copolymers were prepared by thiol‐responsive cleavage of pendant disulfide linkages positioned in the corresponding methacrylate copolymers with narrow molecular weight distribution which were synthesized by a controlled radical polymerization method. With a commercially available multifunctional acrylate as a model ene, photo‐induced thiol‐ene radical polyaddition of these polythiols is competitive to free‐radical homopolymerization of acrylates, yielding crosslinked films exhibiting rapid cure, uniform network, and enhanced mechanical properties; these properties are required for high performance coating materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2860–2868.     

Solvent‐free synthesis of polyacrylamide by frontal polymerization

Polymerization and characterization of polyacrylamide prepared by frontal polymerization are described. Frontally polymerized polyacrylamide is imidized and crosslinked during polymerization. Imide formation was determined by elemental analysis. The addition of commercial polyacrylamide or barium carbonate to the monomer (acrylamide) and initiator (potassium persulfate) decreased the reaction temperature from 235 °C to < 100 °C, thereby reducing imide formation. The commercial polyacrylamide‐diluted product, frontally polymerized polyacrylamide‐diluted product, and the barium carbonate‐diluted product were characterized by IR, TGA, and elemental analysis. Molecular weights of barium carbonate‐diluted samples were determined by light scattering and found to be on the order of one million. Conversion of the barium carbonate‐diluted product was determined to be 76 ± 6%, independent of the amount of diluent over the range 0.8:1–1.5:1. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1129–1135, 2000     

Effect of aqueous and organic solutions on the performance of polyamide thin‐film‐composite nanofiltration membranes

Polyamide/polyacrylonitrile thin‐film‐composite (TFC) nanofiltration (NF) membranes for the separation of oleic acid dissolved in organic solvents (methanol and acetone) were interfacially prepared by the reaction of trimesoyl chloride in an organic phase with an aqueous phase containing piperazine and m‐phenylene diamine. The interfacial reaction was confirmed by an investigation of the attenuated total reflection infrared spectrum. The surface morphology of the polyamide TFC membranes was examined with scanning electron microscopy. The hydrophilic properties of the membrane surfaces were conjectured on the basis of the ζ potential and contact angle. The effects of the monomer concentrations of the monomer blends (aliphatic and aromatic diamines) and drying times on various aspects of membrane performance, such as the solvents (water, alcohols, ketones, and hexane), permeation rates, and organic solute [poly(ethylene glycol) 200 and oleic acid] rejection rates, were investigated. All the membranes showed good solvent resistance. The polar solvent flux for water and methanol was higher than that for a nonpolar solvent (hexane). The membranes gave good rejection rates of oleic acid dissolved in methanol and acetone. The NF membranes were compared with various commercial membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2151–2163, 2002     

Photo‐crosslinked fluorinated thin films from azido‐functionalized random copolymers

Random copolymers of styrene, p‐azidomethylstyrene and 1H,1H,2H,2H‐perfluorodecyl methacrylate were prepared in two steps involving nitroxide‐mediated radical copolymerization and azidation reaction and further characterized by ¹H and ¹⁹F NMR, size exclusion chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Ultrathin films of these azidomethyl‐functionalized fluorinated random copolymers, with thicknesses ranging from 20 to 100 nm, were spin coated onto Si substrates and then crosslinked by ultraviolet irradiation resulting in smooth and insoluble crosslinked fluorinated polymer mats. The surface properties of the supported thin films were investigated by X‐ray photoelectron spectroscopy and water contact angle measurements. These tailored photo‐crosslinked coatings afford a versatile control and homogenization of the wetting properties of different organic and inorganic substrates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3888–3895, 2010     

Proline‐based polymeric monoliths: Synthesis,characterization, and applications as organocatalysts in aldol reaction

Proline‐based polymer monoliths were synthesized via green protocol using lipase‐catalyzed esterification of methacrylic acid and 4‐hydroxyproline. Prolinyl methacrylate thus prepared was polymerized in situ as crosslinked monolith. The monolith was characterized by various techniques such as Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and nitrogen analysis and used as catalyst in aldol reactions. The swelling behavior of the monolith was also studied as function of various external parameters like pH and temperature. The monoliths synthesized with 1% crosslinker was selected as candidate monolith for use as catalyst in aldol reaction, which was studied as a function of time, temperature, substrate structure, and amount of water:EtOH. The catalysts exhibited high efficiency in the cross aldol reaction, especially with the aromatic substrates having electron withdrawing substituent, and also good activity retention was observed when recycleability was studied up to five cycles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1007–1015, 2010     

Concerted reactions of aldehyde groups during polymerization of an aldehyde‐functional benzoxazine

Polymerization reactions of a new aldehyde‐functional benzoxazine (4HBA‐a) were investigated in detail. The curing behavior of 4HBA‐a was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) methods. The results indicate that the disappearance of the aldehyde group from 4HBA‐a and the ring‐opening reaction of 4HBA‐a occur simultaneously. Gases evolved during the curing process of 4HBA‐a were analyzed by thermogravimetric analyzer interfaced with FTIR spectra. The elimination of CO₂ is attributed to the oxidation and decarboxylation of the aldehyde groups. In addition, the crosslink sites of the aldehyde groups in the polymer structure are confirmed by model reactions. A possible reactive position should be sited in ortho position of phenol rather than ortho and/or para positions of N‐phenyl ring. Finally, the crosslinked structures of polymerized 4HBA‐a have been proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry

Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO₂/N₂ selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557     

Synthesis of a new class of triphenylamine‐containing poly(ether‐imide)s for electrochromic applications

A novel triphenylamine (TPA)‐containing bis(ether anhydride) monomer, namely 4,4′‐bis(3,4‐dicarboxyphenoxy)triphenylamine dianhydride, was synthesized and reacted with various aromatic diamines leading to a series of new poly(ether‐imide)s (PEI). Most of these PEIs were soluble in organic solvents and could be easily solution cast into flexible and strong films. The polymer films exhibited good thermal stability with glass‐transition temperatures in the range 211–299 °C. The polymer films exhibited reversible electrochemical processes and stable color changes (from transparent to navy blue) with high coloration efficiency and contrast ratio upon electro‐oxidation. During the electrochemical oxidation process, a crosslinked polymer structure was developed due to the coupling reaction between the TPA radical cation moieties in the polymer chains. These polymers can be used to fabricate electrochromic devices with high coloration efficiency, high redox stability, and fast response time. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 825–838     

Photopatternable substrate‐independent poly(glycidyl methacrylate‐ran‐2‐(acryloyloxy) ethyl 2‐methylacrylate) polymer films for immobilization of biomolecules

We report the synthesis and characterization of a photocrosslinkable copolymer containing reactive epoxy groups for binding biomolecules. The epoxide‐containing copolymer poly(glycidyl methacrylate‐ran‐2‐(acryloyloxy) ethyl 2‐methylacrylate) offers distinct advantages such as ease of application to various substrates, enhanced stability of the bound oligonucleotide, low autofluorescence, and the ability to be photopatterned allowing localization of the linkers. The copolymer uses pendant acryloyl groups to control the crosslinking without sacrificing the epoxide groups. The films were characterized using ellipsometry, atomic force microscopy, and fluorescence microscopy. The films on glass, silicon wafer, and stainless steel showed no appreciable degradation in water, tetrahydrofuran, and acetone for ～4 months. The surface topography for a given thickness of crosslinked film was dictated by the deposition conditions. A 16mer oligonucleotide was immobilized on the thin films. A linear relationship between the film thickness and amount of oligonucleotide immobilized was observed with a maximum signal‐to‐background ratio (S/B) of 225 for a 60‐nm‐thick film, a value 50% higher than the S/B for an epoxide monolayer. The crosslinked films maintained a high fluorescence signal following long aqueous washing which is appealing for biological microarrays, immobilizing proteins, and study of slow differentiating cells where stability of the scaffold is relevant. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5826–5838, 2008     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Pulsed‐laser–deposited and plasma‐polymerized polytetrafluoroethylene (PTFE)‐like thin films: A comparative study on PTFE‐specific properties

Glass‐like and structural first‐order phase transitions are investigated in polytetrafluoroethylene (PTFE) foils and PTFE‐like films prepared by pulsed‐laser deposition (PLD) and plasma polymerization (PP). A structural comparison of the investigated polymers is performed by infrared spectroscopy and dielectric dilatometry. It is shown that dielectric dilatometry (the measurement of the susceptance vs. temperature) provides a simple and elegant means for detecting volumetric transitions in thin nonpolar polymer films. In conventional PTFE foils, the known glass‐like and structural first‐order phase transitions are identified. The structure of pulsed‐laser deposited PTFE strongly depends on the target material, ranging from highly crystalline films showing only structural phase transitions to films strongly deviating from PTFE foils, with structural characteristics comparable to plasma‐polymerized fluorocarbons. The dielectric loss of the highly crystalline PLD films compares favorably with conventional PTFE foils, making the films attractive for new applications in miniature electret devices. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2115–2125, 1999     

Solid‐state amidization and imidization reactions in vapor‐deposited poly(amic acid)

The condensation polymerization of 4,4′‐oxydianiline with pyromellitic dianhydride for the formation of poly(amic acid) and the subsequent imidization for the formation of polyimides were investigated for films prepared with vapor‐deposition polymerization techniques. Fourier transform infrared spectroscopy, thermal analysis, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of films at different temperatures indicated that additional solid‐state polymerization occurred before imidization. The experiments revealed that, upon vapor deposition, poly(amic acid) oligomers formed that had a number‐average molecular weight of about 1500 Da. Between 100–130 °C, these chains underwent an additional condensation reaction and formed slightly higher molecular weight oligomers. Calorimetry measurements showed that this reaction was exothermic [enthalpy of reaction (ΔH) ～ ?30 J/g] and had an activation energy of about 120 kJ/mol. The experimental ΔH values were compared with results from ab initio molecular modeling calculations to estimate the number of amide groups formed. At higher temperatures (150–300 °C), the imidization of amide linkages occurred as an endothermic reaction (ΔH ～ +120 J/g) with an activation energy of about 130 kJ/mol. The solid‐state kinetics depended on the reaction conversion as well as the processing conditions used to deposit the films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5999–6010, 2004     

One‐pot fabrication of robust interpenetrating hydrogels via orthogonal click reactions

Interpenetrating polymer network (IPN) hydrogels have been fabricated through a facile one‐pot approach from tetra/bifunctional telechelic macromonomers with epoxy, amine, azide, and alkyne groups by orthogonal double click reactions: epoxy‐amine reaction and copper‐catalyzed azide‐alkyne cycloaddition. Both the crosslinked networks are simultaneously constructed in water from the biocompatible poly (ethylene glycol)‐based macromonomers. The crosslinking density of each network was finely tuned by the macromonomer structure, permitting control of network molecular weights between crosslinks of the final gels. Compared to corresponding single network gels, the IPN gels containing both tightly and loosely crosslinked networks exhibited superior mechanical properties with shear moduli above 15 kPa and fracture stresses over 40 MPa. The synthetic versatility of this one‐pot approach will further establish design principles for the next generation of robust hydrogel materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1459–1467