Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid‐Crystalline‐Based Medium

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self‐assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD₃OD, [D₆]DMSO, and D₂O. The preparation of the OPA‐based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.     

Reversible crosslinking and decrosslinking of polymers containing alcohol moiety using an acyclic bifunctional vicinal triketone

In this article, we report reversible crosslinking and decrosslinking systems of commercially available alcoholic polymers, using a bifunctional vicinal triketone (bistriketone) as a crosslinking reagent. A small amount of the bistriketone (0.2 equiv of the tricarbonyl moiety relative to the OH group of the polymer) was added to a solution of poly(2‐hydroxyethyl methacrylate) (PHEMA) in dimethyl sulfoxide (DMSO). After 4 days, the networked polymer was obtained as a yellow‐colored gel in 97% yield. Conversely, the resulting gel could be decrosslinked by treatment with MeOH for 4 days to recover the original PHEMA in 94% yield as well as the bistriketone in 54% yield. The network formation and dissociation behaviors were investigated in detail by ¹H NMR and size exclusion chromatography experiments. Similarly to PHEMA, reversible crosslinking and decrosslinking of poly(vinyl alcohol) were achieved by addition of the bistriketone and by treatment of the resulting gel with H₂O/DMSO (1/9, v/v), respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 921–928     

An Alignment Medium for Measuring Residual Dipolar Couplings in Pure DMSO: Liquid Crystals from Graphene Oxide Grafted with Polymer Brushes

Residual dipolar couplings (RDCs) have attracted attention in light of their great impact on the structural elucidation of organic molecules. However, the effectiveness of RDC measurements is limited by the shortage of alignment media compatible with widely used organic solvents, such as DMSO. Herein, we present the first liquid crystal (LC) based alignment medium that is compatible with pure DMSO, thus enabling RDC measurements of polar and intermediate polarity molecules. The liquid crystals were obtained by grafting polymer brushes onto graphene oxide (GO) using free radical polymerization. The resulting new medium offers several advantages, such as absence of background signals, narrow line shapes, and tunable alignment. Importantly, this medium is compatible with π‐conjugated molecules. Moreover, sonication‐induced fragmentation can reduce the size of GO sheets. The resulting anisotropic medium has moderate alignment strength, which is a prerequisite for an accurate RDC measurement.     

Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid-Crystalline-Based Medium

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self-assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD₃OD, [D₆]DMSO, and D₂O. The preparation of the OPA-based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.     

Poly(aryl ether) Dendrons with Monopyrrolotetrathiafulvalene Unit‐Based Organogels exhibiting Gel‐Induced Enhanced Emission (GIEE)

A series of poly(aryl ether) dendrons with a monopyrrolo‐tetrathiafulvalene unit linked through an acyl hydrazone linkage were designed and synthesized as low molecular mass organogelators (LMOGs). Two of the dendrons could gelate the aromatic solvents and some solvent mixtures, but the others could not gel all solvents tested except for n‐pentanol. A subtle change on the molecular structure produces a great influence on the gelation behavior. Note that the dendrons could form the stable gel in the DMSO/water mixture without thermal treatment and could also form the binary gel with fullerene (C₆₀) in toluene. The formed gels undergo a reversible gel–sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. A number of experiments (SEM, FTIR spectroscopy, ¹H NMR spectroscopy, and UV/Vis absorption spectroscopy, and XRD) revealed that these dendritic molecules self‐assembled into elastically interpenetrating one‐dimensional fibrillar aggregates and maintain rectangular molecular‐packing mode in organogels. The hydrogen bonding, π–π, and donor–acceptor interactions were found to be the main driving forces for formation of the gels. Moreover, the gel system exhibited gel‐induced enhanced emission (GIEE) property in the visible region in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by introduction of C₆₀.     

Synthesis of Starburst Oligoanilino[60]fullerene and Poly(Dimethylsiloxane) Triblock Copolymers

Abstract

A new synthetic approach for the fabrication of core‐shell like conducting elastomers was described. The approach utilized the facile intermolecular self‐assembly of poly(dimethylsiloxane) (PDMS) in DMSO leading to formation of a core particle, while soluble oligoaniline (A _x ) segments dispersed in the solution phase resembling a shell overlayer for building the morphology. This morphology was demonstrated by bis[penta(tetraanilinofullereno)] bis(aminopropyl)poly(dimethylsiloxane) [PDMS‐(F5A₄)₂] triblock co‐oligomers synthesized using a functionalized C₆₀ derivative as a linker. Observation of ¹H NMR spectroscopic responses on the PDMS particle formation in DMSO‐d ₆ is consistent with the proposed core‐shell geometry with oligoaniline moieties located at the shell overlayer.     

Synthesis and properties of cationic polyelectrolyte with regioregular polyalkylthiophene backbone and ionic‐liquid like side groups

High‐regioregular poly{3‐[6‐(1‐methylimidazolium‐3‐yl)hexyl]thiophene‐2,5‐diyl bromide}, PMHT‐Br, has been prepared by reaction of high‐regioregular (above 92%) poly[3‐(6‐bromohexyl)thiophene‐2,5‐diyl] with 1‐methylimidazole. PMHT‐Br is soluble in water and water miscible solvents such as methanol, DMSO and shows solvatochromism; λ_max (nm): 423 (H₂O); 435 (MeOH); 452 (DMSO). Increased absorption band broadening observed for aqueous solution as well as NMR spectra in D₂O suggests a micelle‐like structure of PMHT‐Br molecules in these solutions: poly(3‐hexylthiophene) core and 1‐methylimidazolium bromide shell. Despite the disturbing effect of ionic groups, the solid‐state PMHT‐Br shows absorption maximum at 520 nm, the band edge at 660 nm (ca. 1.9 eV), and fluorescence emission with maximum at 635 nm, in a good agreement with the polymer regioregularity. Fluorescence emission maxima: λ_em (nm): 598 (H₂O); 562 (MeOH); 574 (DMSO), occur in a vicinity of corresponding adsorption band edges. Plot of electrical conductivity of PMHT‐Br (measured under the dynamic vacuum conditions, 5 × 10^?5 Pa) versus 1/T shows a break at about 70 °C same as the temperature dependence of λ_max of the solid PMHT‐Br. These breaks indicate an increase in the mobility of polymer segments and ions within PMHT‐Br; however, a thermal analysis did not provide solid evidence for it. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3073–3081, 2010     

Solution,thermal and optical properties of new poly(pyridinium salt)s derived from conjugated quinoline diamines

Several new poly(pyridinium salt)s with quinoline diamine moieties in their backbones with tosylate and triflimide counterion were prepared by either a ring‐transmutation polymerization reaction with bis(pyrylium tosylate) with a series of isomeric quinoline diamines in dimethyl sulfoxide (DMSO) for 48 h at 130–140 °C or a metathesis reaction of the tosylate polymers with lithium triflimide in DMSO at about 60 °C. Their chemical structures were confirmed by FTIR, ¹H and ¹³C NMR spectroscopy, and elemental analysis. Their number‐average molecular weights (M_n) were in the range of 18,000–58,000, and their polydispersities were in the range of 1.12–1.53 as determined by gel permeation chromatography. They had thermal stability in the temperature range of 353–455 °C and glass‐transition temperatures >240 °C. They had good solubility in common organic solvents and were characterized with polarizing optical microscopy (POM) studies for their lyotropic liquid‐crystalline properties. Their light‐emission properties were examined by spectrofluorometry in both the solution and film states. Their quantum yields were also determined. Additionally, their morphologies in the thin‐film states and melt‐drawn fibers were examined with POM, scanning electron microscopy, and transmission electron microscopy techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

One‐Step Synthesis of Multiphase Block Copolymers via Simultaneus Free Radical and Ring Opening Polymerization Using Poly(ethylene oxide) Possessing Azo Group

Multiphase block copolymers having the structure of poly(?‐caprolacton‐b‐etyhlene glycol‐b‐styrene‐b‐ethylene glycol‐b‐?‐caprolacton) were synthesized from poly(ethylene oxide) possesing azo group in the main chain by the combination of free radical polymerization (FRP) of styrene (S) and ring opening polymerization (ROP) of ?‐caprolacton (?‐CL) in one‐step. The block copolymers were characterized ¹H‐NMR and FT‐IR spectroscopy and gel permeation chromatography (GPC). ¹H‐NMR and FT‐IR spectroscopy and GPC studies of the obtained polymers indicate that multiphase block copolymers easily formed as a result of combination FRP and ROP in one‐step.     

Syntheses and characterizations of poly[2‐(dimethylamino)ethyl methacrylate]–poly(propylene oxide)–poly[2‐(dimethylamino)ethyl methacrylate] ABA triblock copolymers

A novel, near‐monodisperse, well‐defined ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(propylene oxide)‐b‐poly[2‐(dimethylamino)ethyl methacrylate], was synthesized via oxyanion‐initiated polymerization. The initiator was a telechelic‐type potassium alcoholate prepared from poly(propylene glycol) and KH in dry tetrahydrofuran. The copolymers produced were characterized by Fourier transform infrared, ¹H NMR, and gel permeation chromatography (GPC). GPC and ¹H NMR analyses showed that the products obtained were the desired copolymers, with narrow molecular weight distributions (ca. 1.09–1.11) very close to that of the original poly(propylene glycol). ¹H NMR, surface tension measurements, and dynamic light scattering all indicated that the triblock copolymer led to interesting aqueous solution behaviors, including temperature‐induced micellization and very high surface activity. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 624–631, 2002; DOI 10.1002/pola.10144     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

Solution,thermal and optical properties of novel poly(pyridinium salt)s derived from conjugated pyridine diamines

Several novel poly(pyridinium salt)s with heterocyclic pyridine moieties in their backbones with tosylate and triflimide counterions were prepared by either ring‐transmutation polymerization reaction of phenylated‐bis(pyrylium tosylate) with isomeric pyridine diamines of 4‐phenyl‐2,6‐bis(4‐aminophenyl)pyridine in dimethyl sulfoxide (DMSO) for 48 h at 130–140 °C or by metathesis reaction of the respective tosylate polymers with lithium triflimide in DMSO at about 60 °C. Their chemical structures were characterized by FTIR, ¹H, ¹³C NMR spectroscopy, and elemental analysis. Their number‐average molecular weights (M_n) were in the range of 8,000–51,000 and their polydispersities in the range of 1.18–2.13 as determined by gel permeation chromatography. They had excellent thermal stabilities of 340–458 °C and high glass transition temperatures >200 °C. As they showed good solubilities in common organic solvents, their solution properties were also characterized for their lyotropic liquid‐crystalline properties with polarizing optical microscopy (POM) studies. Their photoluminescent properties were examined by using a spectrofluorometer in both solution and solid states. Their quantum yields were rather low, which were in the range of 1.3–2.0%. Additionally, hand‐drawn fibers from the melts were examined to determine their morphologies with a number of microscopic techniques including POM, scanning electron microscopy, and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Graft copolymerization of 2‐methacryloyloxyethyl phosphorylcholine to cellulose in homogeneous media using atom transfer radical polymerization for providing new hemocompatible coating materials

To develop new hemopurification systems based on cellulose membrane, we synthesized a graft copolymer of cellulose with poly(2‐methacryloyloxyethyl phosphorylcholine) (MPC) by a metal‐catalyzed atom transfer radical polymerization process in homogeneous media. First, cellulose was dissolved in a DMAc/LiCl solution system, and it reacted with 2‐bromoisobutyloyl bromide to produce macroinitiator (cell‐BiB). Then, MPC was polymerized to the cellulose backbone in a homogeneous DMSO/methanol mixture solution in the presence of cell‐BiB. Characterization with FT‐IR, NMR, and GPC measurements showed that there obtained a graft copolymer of cellulose backbone and poly(MPC) side chains (cell‐PMPC) with well‐defined structure, indicating a controlled/“living” radical polymerization. The proteins adsorption studies showed that cellulose membranes modified by the as‐prepared cell‐PMPC owns good protein adsorption resistance. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3306–3313, 2008     

The application of copper(II) deactivator on the single‐electron transfer living radical polymerization of tert‐butyl acrylate

We demonstrate the living radical polymerization of tert‐butyl acrylate (tBA) applying the SET mechanism, employing methyl 2‐bromopropionate (MBP) as initiator in dimethyl sulfoxide (DMSO) at ambient temperature. It is observed that introducing copper bromide into the catalyst system is necessary for controlling on the SET‐LRP polymerization of tBA. In this work, we make major investigation for the effect of the different stoichiometry quantity of copper bromide on the polymerization. Experiments show that the polymerization achieves better control with increasing the stoichiometry quantity of copper(II) deactivator. The structural analysis of the resulting polymers by ¹H NMR demonstrates the successful synthesis of poly(tBA)s by SET‐LRP in DMSO. Moreover, this work is helpful to the SET‐LRP of other monomers and is expected to expand the application of SET‐LRP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2793–2797, 2010     

One‐pot synthesis of 2‐phenyl‐2‐oxazoline‐containing quasi‐diblock copoly(2‐oxazoline)s under microwave irradiation

The microwave‐assisted statistical copolymerization of 2‐phenyl‐2‐oxazoline with 2‐methyl‐2‐oxazoline or 2‐ethyl‐2‐oxazoline is discussed in this contribution. Kinetic studies of these statistical copolymerizations as well as reactivity ratio determinations were performed to investigate the monomer distribution in these copoly(2‐oxazoline)s, demonstrating the formation of quasi‐diblock copolymers. In addition, the synthesis of copolymer series with monomer concentrations ranging from 0 to 100 mol % is described. These copolymer series were characterized with ¹H NMR spectroscopy, gas chromatography, and gel permeation chromatography. Moreover, the glass‐transition temperatures and solubility of these copolymers were studied, and this revealing better mixing of poly(2‐methyl‐2‐oxazoline) (pMeOx) with poly(2‐phenyl‐2‐oxazoline) (pPhOx) than poly(2‐ethyl‐2‐oxazoline) (pEtOx) with poly(2‐phenyl‐2‐oxazoline) (pPhOx). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 416–422, 2007.     

Micelle formation and sol–gel transition behavior of comb‐like amphiphilic poly((PLGA‐b‐PEG)MA) copolymers

Comb‐like amphiphilic poly(poly((lactic acid‐co‐glycolic acid)‐block‐poly(ethylene glycol)) methacrylate (poly((PLGA‐b‐PEG)MA)) copolymers were synthesized by radical polymerization. (PLGA‐b‐PEG)MA macromonomer was prepared by ring‐opening bulk polymerization of DL ‐lactide and glycolide using purified poly(ethylene glycol) monomethacrylate (PEGMA) as an initiator. (PLGA‐b‐PEG)MA macromonomer was copolymerized with PEGMA and/or acrylic acid (AA) by radical polymerization to produce comb‐like amphiphilic block copolymers. The molecular weight and chemical structure were investigated by GPC and ¹H NMR. Poly((PLGA‐b‐PEG)MA) copolymer aqueous solutions showed gel–sol transition behavior with increasing temperature, and gel‐to‐sol transition temperature decreased as the compositions of the hydrophilic PEGMA and AA increased. The gel‐to‐sol transition temperature of the terpolymers of the poly((PLGA‐b‐PEG)MA‐co‐PEGMA‐co‐AA) also decreased when the pH was increased. The effective micelle diameter obtained from dynamic light scattering increased with increasing temperature and with increasing pH. The critical micelle concentration increased as the composition of the hydrophilic monomer component, PEGMA and AA, were increased. The spherical shape of the hyperbranched polymers in aqueous environment was observed by atomic force microscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1954–1963, 2008     

Direct Synthesis of Poly(potassium 3‐sulfopropyl methacrylate) Cylindrical Polymer Brushes via ATRP Using a Supramolecular Complex With Crown Ether

A supramolecular complex between an ionic monomer 3‐sulfopropyl methacrylate (SPMAK) and crown ether 18‐crown‐6 (18C6) has been employed to prepare a strong anionic cylindrical polyelectrolyte brush poly(potassium 3‐sulfopropyl methacrylate) (PSPMAK) by atom transfer radical polymerization (ATRP) in polar solvent dimethyl sulfoxide (DMSO). This strategy solved the problem of the solubilities of the incompatible hydrophobic poly‐initiator and hydrophilic ionic monomer. The formation of the PSPMAK brush is well proven by ¹H NMR, aqueous gel permeation chromatography (GPC), dynamic light scattering (DLS), static light scattering (SLS), atomic force microscopy (AFM), and cryogenic transmission electron microscopy (cryo‐TEM) measurements. Cleavage of the side chains and further analysis reveal that the initiating efficiency of the polymerization is as low as 0.35.

     

Preparation of methoxy poly(ethylene glycol)/polyester diblock copolymers and examination of the gel‐to‐sol transition

Diblock copolymers consisting of methoxy poly(ethylene glycol) (MPEG) and poly(?‐caprolactone) (PCL), poly(δ‐valerolactone) (PVL), poly(L ‐lactic acid) (PLLA), or poly(lactic‐co‐glycolic acid) (PLGA) as biodegradable polyesters were prepared to examine the phase transition of diblock copolymer solutions. MPEG–PCL and MPEG–PVL diblock copolymers and MPEG–PLLA and MPEG–PLGA diblock copolymers were synthesized by the ring‐opening polymerization of ?‐caprolactone or δ‐valerolactone in the presence of HCl · Et₂O as a monomer activator at room temperature and by the ring‐opening polymerization of L ‐lactide or a mixture of L ‐lactide and glycolide in the presence of stannous octoate at 130 °C, respectively. The synthesized diblock copolymers were characterized with ¹H NMR, IR, and gel permeation chromatography. The phase transitions for diblock copolymer aqueous solutions of various concentrations were explored according to the temperature variation. The diblock copolymer solutions exhibited the phase transition from gel to sol with increasing temperature. As the polyester block length of the diblock copolymers increased, the gel‐to‐sol transition moved to a lower concentration region. The gel‐to‐sol transition showed a dependence on the length of the polyester block segment. According to X‐ray diffraction and differential scanning calorimetry thermal studies, the gel‐to‐sol transition of the diblock copolymer solutions depended on their degrees of crystallinity because water could easily diffuse into amorphous polymers in comparison with polymers with a crystalline structure. The crystallinity markedly depended on both the distinct character and composition of the block segment. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5784–5793, 2004     

Non‐Ideal Behaviour and Solution Interactions in Binary DMSO Solutions

The structure and dynamics of hydrogen‐bonded structures are of significant importance in understanding many binary mixtures. Since self‐diffusion is very sensitive to changes in the molecular weight and shape of the diffusing species, hydrogen‐bonded associated structures in dimethylsulfoxide–methanol (DMSO–MeOH) and DMSO–ethanol (DMSO–EtOH) mixtures are investigated using nuclear magnetic resonance (NMR) diffusion experiments and molecular dynamics (MD) simulations over the entire composition range at 298 K. The self‐diffusion coefficients of DMSO–MeOH and DMSO–EtOH mixtures decrease by up to 15% and 10%, respectively, with DMSO concentration, indicating weaker association as compared to DMSO–water mixtures. The calculated heat of mixing and radial distribution functions reveal that the intermolecular structures of DMSO–MeOH and DMSO–EtOH mixtures do not change on mixing. DMSO–alcohol hydrogen‐bonded dimers are the dominant species in mixtures. Direct comparison of the simulated and experimental data afford greater insights into the structural properties of binary mixtures.     

Composite alignment media for the measurement of independent sets of NMR residual dipolar couplings

The measurement of independent sets of NMR residual dipolar couplings (RDCs) in multiple alignment media can provide a detailed view of biomolecular structure and dynamics, yet remains experimentally challenging. It is demonstrated here that independent sets of RDCs can be measured for ubiquitin using just a single alignment medium composed of aligned bacteriophage Pf1 particles embedded in a strained polyacrylamide gel matrix. Using this composite medium, molecular alignment can be modulated by varying the angle between the directors of ordering for the Pf1 and strained gel matrix, or by varying the ionic strength or concentration of the Pf1 particles. This approach offers significant advantages in that greater experimental control can be exercised over the acquisition of multi-alignment RDC data while a homogeneous chemical environment is maintained across all of the measured RDC data.