Supramolecular structures of poly(γ-benzyl-L-glutamate) self-assembled on mica surface

This article reports the results of structural studies of poly (γ-benzyl-L -glutamate) (PBLG) layers self-assembled from dilute solutions in organic solvents on mica surface. Polarized dynamic light scattering and atomic force microscopy were used to study polymer properties in solutions and on the surface. The hierarchy of self-assembly from PBLG solutions in different solvents was investigated as a function of polymer concentration and solvent polarity. We show that the surface–polymer interaction is suppressed in polar solvents that is interpreted in terms of suppressed charge–dipole interaction. The transformation of the PBLG surface structure occurs upon addition of different amounts of trifluoroacetic acid to polymer solution in dioxane. Rigid-rod PBLG molecules experience rod–globular transition while assembling on nonmodified mica from the very dilute solutions. A scheme is proposed describing different stages of PBLG fibrogenesis on a charged surface. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1567–1577, 1998     

Thermoreversible gelation of helical polypeptide/single‐walled carbon nanotubes and their solid‐state structures

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate)s (PBLGs) having well‐defined polymer molecular weight (M_n = 7.5–21.1 kg·mol^?1) and molecular weight distribution (PDI = 1.05–1.20) by a graft‐to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG‐functionalized SWCNTs (PBLG‐SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (ΔH_m) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG‐SWCNTs. Small‐angle X‐ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG‐SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG‐SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG‐SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Rheology of concentrated solutions of helical polypeptides

Rheological studies were carried out on concentrated m-cresol solutions of two helical synthetic polypeptides; poly-γ-benzyl-L -glutamate (PBLG; molecular weight, 150,000) and poly-?-carbobenzyloxy-L -lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01–16,000 sec^?1 to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1–400 and 0.1–63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m-cresol solutions at room temperature constitutes evidence that the inverse coil-helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial ratio, due to helix flexibility.     

Carboxylic acid functionalization of nylon 6 by radiation grafting and conversion to zinc salts: Effects on physical properties

 Functionalization of polymers by grafting monomeric species on to the backbone of molecular chains with the use of γ-radiation has been used extensively. In this work methacrylic acid was grafted onto a commercial grade of polycaproamide (Nylon 6) by preirradiating the polymer granules to 15 kGy at a rate of 1.0 kGy per hour and subsequently immersing these in a 10% aqueous solution of methacrylic acid in the presence of small quantities of FeSO₄ as homopolymerization inhibitor. The polymer was subsequently neutralized by mixing it with zinc acetylacetonate in a laboratory scale melt mixing device. The acid-grafting polymer modification resulted in an increase in glass transition temperature, while the addition of zinc acetylacetonate gave rise to two transitions: The lower transition corresponds to a miscible mixture of free polyamide and acid-grafted polymer, both plasticized with undecomposed zinc compound, while the upper transition corresponds to the zinc salt of the acid grafted polyamide. Through rheological measurements it was shown that both the acid-grafted polymer and the derived zinc salt have a branched structure, possibly containing also some crosslinked domains. Large improvements in solvent resistance were observed for both type of polymer modifications. Received: 13 December 1996 Accepted: 10 February 1997     

Dielectric relaxation in concentrated solutions of poly(γ-benzyl-L-glutamate)

Measurements of dielectric constant and loss, broad-line nuclear magnetic resonance, and differential thermal analysis of concentrated solutions of poly(γ-benzyl-L -glutamate) (PBLG) were carried out to determine the effects of intermolecular interactions on the mobility of the side group and the solvent (dichloromethane or dioxane). Only one dielectric loss peak due to the cooperative motion of the side group and the solvent was found. The activation energy of this relaxation process varied from 3 to 47 kcal/mole with increasing concentration of PBLG from 20 to 100% by weight accompanied with steep increases at about 40 and 80%. This result is explained as due to entanglement of neighboring side groups. In NMR, narrowing of the line was observed near the temperature where the dielectric loss was observed. The glass transition was also observed by differential thermal analysis. From these results it was concluded that the relaxation observed in PBLG solution and in pure PBLG have the nature of primary or α relaxations.     

Supramolecular polymer/metal salt complexes containing quadruple hydrogen bonding units

A supramolecular material containing quadruple hydrogen bonding sites was prepared by reacting the amines of methyl isocytosine and the epoxy groups of poly (ethylene glycol diglycidyl ether). This supramolecular polymer was complexed with metal salt, that is potassium iodide, to produce polymer electrolytes, and their physical properties, specific interactions, and conductivity behavior were investigated. The ionic conductivity of polymer electrolytes continuously increased with increasing salt concentration up to 0.4 of salt weight fraction, presenting usually high solubility limit of salt in the supramolecular polymer. Wide angle X‐ray scattering data also presented that the metal salt was completely dissolved in the supramolecular polymer up to 0.4 of salt weight fraction. Upon the introduction of metal salt, the mechanical properties of the supramolecular polymer were significantly enhanced by around 10 times and the glass transition temperature of the polymer increased by about 50 °C, as revealed by complex melt viscosities and differential scanning calorimetry. These unusual behaviors of salt solubility and mechanical properties for supramolecular polymer/metal salt complexes were attributed to the strong, additional metal ion coordination to hydrogen bonding sites as well as ether oxygens of polymer matrix, as supported by FTIR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3181–3188, 2007     

Synthesis of ω‐sulfonated polystyrene via reversible addition fragmentation chain transfer polymerization and postpolymerization modification

The synthesis of chain‐end sulfonated polystyrene [PS (ω‐sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymerization modification was investigated by two methods. In the first method, the polymer was converted to a thiol‐terminated polymer by aminolysis. This polymer was then sulfonated by oxidation of the thiol end‐group with m‐chloroperoxybenzoic acid (m‐CPBA) to produce a sulfonic acid end‐group. In the second method, the RAFT‐polymerized polymer was directly sulfonated by oxidation with m‐CPBA. After purification by column chromatography, ω‐sulfonated PS was obtained by both methods with greater than 95% end‐group functionality as measured by titration. The sulfonic acid end‐group could be neutralized with various ammonium or imidazolium counter ions through acid–base or ionic metathesis reactions. The effect of the ionic end‐groups on the glass transition temperature of the PS was found to be consistent with what is known for PS ionomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(γ‐benzyl‐L‐glutamate)‐functionalized single‐walled carbon nanotubes from surface‐initiated ring‐opening polymerizations of N‐carboxylanhydride

Single‐walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ‐benzyl‐L ‐glutamate) (PBLG) by ring‐opening polymerizations of γ‐benzyl‐L ‐glutamic acid‐based N‐carboxylanhydrides (NCA‐BLG) using amino‐functionalized SWCNTs (SWCNT‐NH₂) as initiators. The SWCNT functionalization has been verified by FTIR spectroscopy and transmission electron microscopy. The FTIR study reveals that surface‐attached PBLGs adopt random‐coil conformations in contrast to the physically absorbed or bulk PBLGs, which exhibit α‐helical conformations. Raman spectroscopic analysis reveals a significant alteration of the electronic structure of SWCNTs as a result of PBLG functionalization. The PBLG‐functionalized SWCNTs (SWCNT‐PBLG) exhibit enhanced solubility in DMF. Stable DMF solutions of SWCNT‐PBLG/PBLG with a maximum SWCNTs concentration of 259 mg L^?1 can be readily obtained. SWCNT‐PBLG/PBLG solid composites have been characterized by differential scanning calorimetry, thermogravimetric analysis, wide/small‐angle X‐ray scattering (W/SAXS), scanning electron microscopy, and polarized optical microscopy for their thermal or morphological properties. Microfibers containing SWCNT‐PBLG and PBLG can also be prepared via electrospinning. WAXS characterization reveals that SWCNTs are evenly distributed among PBLG rods in solution and in the solid state where PBLGs form a short‐range nematic phase interspersed with amorphous domains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2340–2350, 2010     

Synthesis and Characterization of H‐bonded Side‐Chain Liquid‐Crystalline Polysiloxanes

Smectic Liquid‐crystalline (LC) polysiloxanes P1～P7 were prepared using cholesteryl 6‐undec‐10‐enoyloxy‐naphthalene‐2‐carboxylate and cholesteryl 3‐sulfo‐4‐undec‐10‐enoyloxy‐benzoate in a one‐step reaction with sulfonic acid group contents ranging between 0 and wt 4.39%. With an increase of sulfonic acid groups, the glass transition temperature rose slightly; while the temperature of clear point decreased. As sulfonic groups increased, H‐bonding interaction strengthened, resulting in an increase of glass transition temperature. On the other hand, aggregates of H‐bond derived from sulfonic acids would destroy the homogeneous rigid moieties and the high‐ordered structure, resulting in a temperature of clear point decreased. In X‐ray measurement, all the polymers displayed sharp strong peaks around 2θ≈2.6° and broad peaks around 2θ ≈16.6°. The broad peaks at wide‐angle are similar, but there is great different at low angles. For the polymer without sulfonic acid, the only one strong peak at low angle indicates high‐ordered lamellar structure due to homogeneous rigid moieties. For the polymers containing more sulfonic acid, two sharp peaks appeared at low angles, and the intensities of these two peaks varied. With increase of sulfonic acid groups in the polymer systems, the hydrogen‐bonding aggregates in domains would divide the homogeneous rigid mesogens into two kinds of nanophases, that is, one containing non H‐bond mesogens and another involving H‐bonding aggregated mesogens. These two different nanophases result in different lamellar spacings.     

Surfactant effect on the lower critical solution temperature of poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups

 The surfactant effect on the lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups was examined in terms of molecular interactions between the polyphosphazenes and surfactants including various anionic, cationic, and nonionic surfactants in aqueous solution. Most of the anionic and cationic surfactants increased the LCST of the polymers: the LCST increased more sharply with increasing length and hydrophobicity of the hydrophobic part of the surfactant molecule. The ΔLCSTs (T _0.03M− T _0M), the change in the LCST by addition of 0 and 0.03 M sodium dodecyl sulfate (SDS), were found to be 7.0 and 14.5 °C for the polymers bearing ethyl esters of glycine and aspartic acid, respectively. The LCST increase of poly(organophosphazene) having a more hydrophobic aspartic acid ethyl ester was 2 times larger compared with that of the polymer having glycine ethyl ester as a side group. The binding behavior of SDS to the polymer bearing glycine ethyl ester as a hydrophobic group was explained from the results of titration of the polymer solutions containing SDS with tetrapropylammonium bromide. Graphic models for the molecular interactions of polymer/surfactant and polymer/surfactant/salt in aqueous solutions were proposed. Received: 17 February 2000/Accepted: 25 April 2000     

Controlled Nanopores in Thin Films of Nonstoichiometrically Supramolecularly Assembled Graft Copolymers

Herein, nanometer‐scale morphologies of graft‐copolymer‐like supramolecular thin films, composed of sulfonic acid terminated polystyrene (SPS) and poly(2‐vinylpyridine) (P2VP), and their application to antireflection coatings were investigated. The intermolecular complexes of SPS and P2VP, formed through nonstoichiometric multiple hydrogen bonding between the sulfonic acid group of SPS and the nitrogen atom in pyridine unit of P2VP, occurring in film deposition allowed for the formation of spherical micelles (with SPS and P2VP as the corona and core, respectively) in the thin film. Interestingly, the domain size of the micelles was tunable from approximately 20 to 90 nm on average by controlling either the blend ratio of components or the concentration of polymer solution. Furthermore, nanoporous thin films could be easily prepared by removing the core of micelle‐based nanostructures by using a simple solvent etching process, leaving sulfonic acid groups on the surface of nanopores, which can be utilized as potential functional sites. Those resultant nanoporous thin films were conveniently employed as an antireflection layer on a glass substrate, giving a maximum 97.8 % transmittance in the visible wavelength range.     

Synthesis of a novel tetracationic acidic organic salt based on DABCO and its applications as catalyst in the Knoevenagel condensation reactions in water

Synthesis of a novel tetracationic acidic organic salt based on DABCO containing two sulfonic acid groups in the skeleton and four hydrogensulfate groups as counterion is described. Its catalytic efficiency in the Knoevenagel condensation of aldehydes with active cyclic methylene compounds in water is investigated. While 2,2'-(phenylmethylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) derivatives were obtained in 40–98% isolated yields in the reaction of aldehydes with dimedone, the corresponding Knoevenagel adducts were provided in 85–95% yields using 1,3-dimethylbarbituric acid. In addition, a DABCO-based polycationic organic salt polymer was prepared and characterized for the first time.     

离聚物共混体系在溶液中分子间缔合的粘度研究

研究了磺化聚苯乙烯离聚体／聚（苯乙烯 ４ 乙烯吡啶）共混体系、磺化聚苯醚离聚体／聚（苯乙烯 ４ 乙烯吡啶）共混体系和磺化聚苯醚离聚体／胺化聚苯醚共混体系在氯仿／甲醇混合溶剂中的粘度行为，结果表明，和它们分别对应的不含离子基的共混物相比，这三个共混体系都表现出较高的比浓粘度．这是由于体系中的酸基及其盐和含氮碱基的引入，在共混组分间产生了强烈的离子相互作用，从而导致分子间的缔合，使比浓粘度提高．并讨论了溶剂体系、功能基种类及共混组分的主链结构等因素对这种分子间缔合作用的影响．     

Response of protonic acid‐doped poly(o‐anisidine)/poly(vinyl alcohol) composites to relative humidity and role of dopant anions

Various protonated poly(o‐anisidine) (PoAN)/poly(vinyl alcohol) (PVA) composites were prepared with different types of acids: sulfuric (SA), p‐toluene sulfonic (TSA), camphor sulfonic (CSA), and p‐dodecylbenzene sulfonic (DBSA). In the visible spectrum of each composite in dimethyl sulfoxide, three absorption peaks were observed at 440, 620, and 860 nm. The peaks at 440 and 860 nm, which were enhanced with the increasing content of acid‐doped PoAN in the PVA matrix, were attributed to the radical cation and localized polaron generated in the conducting polymer. However, the peak at 620 nm was ascribed to the emeraldine base (EB) form of PoAN; that is, a portion of the acid was detached from the conducting polymer to form EB‐PoAN and free acid. The linear dependence of the logarithmic electrical conductivity on the variation of humidity, which was observed for all the composites, was caused by the salt–base transition of the conducting polymer, that is, by the movement of free acid between the active sites of the conducting polymer and the strongly bound water existing in PVA, which in turn depended directly on the environmental humidity. The response time of the composites to humidity was shortened with a decrease in the size of the dopant anions: DBSA > CSA > TSA > SA. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4343–4352, 2000     

Synthesis and properties of novel benzimidazole‐containing sulfonated polyethersulfones for fuel cell applications

A novel series of benzimidazole‐containing sulfonated poly(arylene sulfones)s with controllable amount of basic 2,6‐bis(benzimidazol‐2‐yl)pyridine (BIP) and sulfonic acid groups have been prepared by the copolycondensation of a new BIP‐containing arylene difluoride monomer (DFSBIP) with a sulfonated arylene difluoride (DSDFS) and 4,4′‐biphenol (BP). All the resulting polymers have high molecular weights, good thermal stability, and can form uniform and tough membranes by simple solution casting. Because of the strong acid–base interaction between BIP and sulfonic acid groups, ionic crosslinking networks forms that resulted in polymer membranes with good dimensional stability in water even at high temperature (e.g., 100 °C). The ion exchange capacity (IEC) of the polymer membranes was investigated through a new simple pH‐determination method. A comparison between the experimental IEC values with the calculated ones based on the polymer structures indicated that each BIP unit interacted with one sulfonic acid group. Thus, by controlling the relative content of BIP units and sulfonate groups in the polymers, the intra‐ and intermolecular acid–base interactions could be readily optimized so as to achieve polymers with high IEC values, high proton conductivities as well as low swelling ratios, demonstrating good potential for proton exchange membrane applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1920–1929, 2009     

Phase transition in dilute solution of poly(γ-benzyl-L-glutamate) in dichloromethane at a low temperature

The dielectric constant of solutions of poly(γ-benzyl-L -glutamate) (PBLG) in dichloromethane shows a jump near 195°K, irrespective of frequency. Therefore, the discontinuity is not a dispersion phenomenon but a phase transition in the thermodynamic sense. The transition temperature is independent of the concentration in the range from 0.01 to 10% by weight, but it increases linearly with the logarithm of the molecular weight of PBLG. The height of the jump depends strongly on frequency, concentration, and molecular weight. The viscosity also changes abruptly at 195°K. These results suggest that the PBLG molecule forms a cluster like a liquid crystal or is in a random coil state below the transition point.     

Molecular dynamics of grafted PBLG in the swollen and in the dried state

A novel technique to contact (ultra‐) thin polymer layers is presented which enables to compare the molecular dynamics in grafted films of poly(γ‐benzyl‐L ‐glutamate) (PBLG) to that of the bulk polymer by means of dielectric spectroscopy. Two relaxation processes are observed which are assigned to restricted fluctuations of the helical main chains and to the dynamic glass transition of the side chains. Furthermore, the swelling behavior of PBLG is studied.     

Rheological studies of the interactions in cellulose/ethylene diamine/salt systems

Degree of polymerization (DP) of cellulose was measured to confirm that aging time and salt concentration did not cause cellulose degradation. Dynamic rheological studies of cellulose solutions were carried out to probe the evolving interactions between cellulose and ethylene diamine (EDA)/salt solvent system. Potassium thiocyanate (KSCN) was used as the salt in these studies. Steady shear studies indicated that all solutions exhibited shear‐thinning behavior. The empirical Cox‐Merz rule did not hold true for the cellulose system with weak gel microstructure. The shear viscosities at the shear rates explored decreased with aging time. The zero‐shear viscosity, however, increased with increasing salt concentration. Oscillatory shear studies were investigated and the time temperature superposition (TTS) method was used to extend the experimental frequency range of the instrument. The results showed that the average relaxation time of the cellulose system decreased as the sample aged and increased with increasing salt concentration, indicative of dynamic interactions between cellulose and the solvent system in solution. The conformations of cellulose chains were constantly changing over time. The system gelled when the salt concentration was increased to a critical point. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2326–2334, 2008     

Structure and dielectric relaxations of antibacterial sulfonated polystyrene and silver nanocomposites

Structure and dielectric relaxations of antibacterial sulfonated polystyrene (SPS) and silver nanocomposites (SPS/Ag) were investigated via broadband dielectric spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, and wide‐angle X‐ray diffraction. SPS/Ag nanocomposites were prepared from SPS containing 2, 4, and 7 mol% of acid contents, followed by ion exchange and a reduction process. Silver nanoparticles were formed in the structural cavities of SPS films. The single glass transition temperature of the SPS copolymers was observed and increased with increasing acid contents and more enhanced with embedded silver nanoparticles because of the restriction of the polymer chain movement. The particle size of embedded silver nanoparticles was about 10 nm and well dispersed in SPS matrices. Four dielectric relaxations were observed above the glass transition temperature, and they were attributed to the fast segmental relaxation, the slow‐hindered segmental relaxation, relaxations associated with Maxwell–Wagner–Sillars interfacial polarization and electrode polarization. Weak local relaxations were observed due to the motion of sulfonated phenyl groups. Copyright © 2014 John Wiley & Sons, Ltd.     

Viscosity enhancement of complexed solutions formed through the complexation of nonionic water‐soluble polymers with chemically complementary structures in aqueous media

The intermacromolecular complexation of polymers with chemically complementary structures in aqueous media is a new approach to modifying polymer solutions, especially to enhance solution viscosity. In this study, complexed solutions formed through the hydrogen‐bonding complexation of several nonionic water‐soluble polymer pairs—poly(acrylic acid) (PAA) with polyacrylamide (PAM), PAM with poly(ethylene oxide) (PEO), PAA with poly(vinyl alcohol) (PVA), and PEO with PVA—were prepared, and the viscosity enhancement of the complexed solutions were studied with vision spectrophotometry and viscometry. The effects of the polymer concentration, polymer molecular weight, and pH value of the polymer solution on the intermacromolecular interactions were investigated through a comparison of the viscosity enhancement factor R of different complexed solutions. The results show that the viscosity of the PAA/PAM complexed solution is much higher than that of its constituents, whereas that of the PAM/PEO and the PAA/PVA complexed solutions are between the viscosities of their constituents but are higher than the theory values calculated from the blending rule of two polymer solutions. These results indicate that in the complexed solutions there exist interactions between the macromolecules with chemically complementary structures, although the interactions are quite different for the different complexed systems. It is the interactions that lead to an association of the polymers and, hence, an obvious enhancement in the solution viscosity and the resistance of the polymer solutions to shearing. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1069–1077, 2000