Model Compounds Of Polymers Research Articles

Facile Synthesis of Liquid Crystal Dimers Bridged with a Phosphonic Group.

Liquid crystal (LC) dimers with well-defined composition and structure arouse broad attentions for their exhibiting LC properties beyond conventional low molar mass mesogens and serving as fascinating model compounds for LC polymers. Here in this work, a series of LC dimers bridged with a phosphonic group have been synthesized through a facile free radical mediated addition reaction between hypophosphorous acid and vinyl terminated cyanobiphenyl mesogens with variant length alkyl spacers. In addition, two esterified derivatives and a group of mono-addition homologues with a terminal phosphonic acid group have also been prepared for comparison study. All the newly synthesized compounds exhibit monotropic nematic (N) phase with typical schlieren textures except for the LC dimer with the longest eleven-methylene spacer, which surprisingly shows twist-bend nematic (NTB ) phase directly from the isotropic state upon cooling. Moreover, the thermal transition properties such as the nematic-isotropic transition temperatures and associated entropy changes of the series LC dimers display a modest odd-even effect. Furthermore, both the LC dimers and the mono-addition homologues in N phase are quite easy to achieve homeotropic alignment upon annealing thanks to the supramolecular interactions between the introduced phosphonic acid group and the hydroxylated glass surface. This work thus provides a novel synthesis strategy for a class of LC materials bridged with a phosphonic acid group prone to further functionalization, which may serve as promising vertical alignment agents and pave the way for developing a new kind of functionalized LC materials of NTB phase.

Selective Metal‐Complexation on Polymeric Templates and Their Investigation via Isothermal Titration Calorimetry

AbstractSelective complexation of metal ions represents a powerful tool for the development of versatile supramolecular architectures. While research in the field of molecular devices and machinery is sophisticated, the selective formation of metal complexes is not prevalent in polymer chemistry. Thus, the implementation of orthogonal binding concepts into a polymeric matrix is presented. In this context, an end‐functionalized poly(N‐isopropylacrylamide) (PNIPAm) carrying zinc‐porphyrin (ZnTPP) as well as a terpyridine (tpy) ligand side by side is utilized. With these binding sites, the polymer can simultaneously interact with a pyridine moiety via a ZnTPP interaction and a terpyridine unit by the formation of a bis‐terpyridine complex. The complexation behavior of this polymer and different model compounds is intensively investigated by isothermal titration calorimetry. The obtained results indicate that the reported orthogonality of these two systems is successfully transferred into a functional polymeric architecture.

Reactivity of an air-stable dihydrobenzoimidazole n-dopant with organic semiconductor molecules

Summary 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole, N-DMBI-H, is widely used as an air-stable n-dopant for organic semiconductors. Here, its reactivity is investigated with a variety of imide- and amide-containing semiconductor molecules that have reduction potentials in the range −0.54 to −1.10 V versus ferrocene. Reaction rates correlate poorly with these potentials. The more reactive of the imides form the corresponding radical anions cleanly, but kinetic isotope studies using N-DMBI-D indicate that the reaction proceeds via an initial hydride- or hydrogen-transfer step. For an amide- and ester-rigidified bis(styryl)benzene derivative the hydride-reduced product is stable under an inert atmosphere and can be observed directly; the radical anion can only be obtained in sub-stoichiometric yield and under certain reaction conditions. On the other hand, (N-DMBI)2 rapidly reduces all the imides and amides examined to the corresponding radical anions. The implications of these findings for dopant selection and use are discussed.

Labile Dissolved Organic Matter Compound Characteristics Select for Divergence in Marine Bacterial Activity and Transcription.

Bacteria play a key role in the planetary carbon cycle partly because they rapidly assimilate labile dissolved organic matter (DOM) in the ocean. However, knowledge of the molecular mechanisms at work when bacterioplankton metabolize distinct components of the DOM pool is still limited. We, therefore, conducted seawater culture enrichment experiments with ecologically relevant DOM, combining both polymer and monomer model compounds for distinct compound classes. This included carbohydrates (polysaccharides vs. monosaccharides), proteins (polypeptides vs. amino acids), and nucleic acids (DNA vs. nucleotides). We noted pronounced changes in bacterial growth, activity, and transcription related to DOM characteristics. Transcriptional responses differed between compound classes, with distinct gene sets (“core genes”) distinguishing carbohydrates, proteins, and nucleic acids. Moreover, we found a strong divergence in functional transcription at the level of particular monomers and polymers (i.e., the condensation state), primarily in the carbohydrates and protein compound classes. These specific responses included a variety of cellular and metabolic processes that were mediated by distinct bacterial taxa, suggesting pronounced functional partitioning of organic matter. Collectively, our findings show that two important facets of DOM, compound class and condensation state, shape bacterial gene expression, and ultimately select for distinct bacterial (functional) groups. This emphasizes the interdependency of marine bacteria and labile carbon compounds for regulating the transformation of DOM in surface waters.

Effects of Hydrothermal Reaction of Sulfuric Acid Lignin from Cryptomeria japonica for Industrial Utilization

Sulfuric acid lignin (SAL), one of the major biorefinery industry residues from the acid saccharification process on lignocellulosic materials for bio-fuel generation, is becoming a major problem for the sustainable development of the bio-refinery industry. Meanwhile, the recalcitrant and highly complex structure of SAL makes it insoluble in water and other organic solvents, resulting in a low reactivity. This study investigated the effects of hydrothermal reactions on SAL to enhance its solubility and reactivity. A hydrothermal reaction was first conducted on SAL from Cryptomeria japonica to obtain a completely water-soluble lignin. Fourier transform infrared spectroscopy, gel permeation chromatography, gas chromatography, and nuclear magnetic resonance (NMR) analyses revealed that the hydrothermal reaction of the SAL caused depolymerisation, demethylation, and the introduction of phenolic hydroxyls. Furthermore, another experiment was conducted on synthesizing a lignin polymer model compound (DHP) with 13C-labelled on the aromatic ring, followed by hydrothermal reaction and acetylation. Detailed structural information of DHP under hydrothermal reaction was obtained by solid-state cross polarization magic angle spinning NMR analysis. Reactivity of the hydrothermally treated SAL was enhanced by the hydrothermal reaction through the reversed increasing of the phenolic hydroxyl/aliphatic hydroxyl ratio in the condensed lignin units.

Theoretical studies on bond dissociation enthalpies for model compounds of typical plastic polymers

The polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), bisphenol A polycarbcconate (PC) comprise above 80% of plastic polymers. The bond dissociation enthalpies for model compounds of the six typical plastic polymers were calculated by using density functional theory methods, and the possible degradation mechanisms of these plastic polymers were proposed. The degradation of PE and PP is mainly main-chain random scission mechanism; the PS degradation is mainly zipper scission and main-chain random scission mechanism; the PVC degradation is mainly branched-chain scission mechanism; the PET and PC decompose mainly through C-O homolytic cleavage, C-C homolytic cleavage and concerted reaction.

Synthesis and mesomorphic behavior of symmetrical chiral liquid crystal dimers incorporating ester linked biphenyl- naphthyl cores and terminal vinyl group

ABSTRACTA series of symmetrical chiral, liquid crystal dimeric molecules possessing ester- linked, biphenyl-naphthyl cores with varied spacer lengths and terminal vinyl groups have been synthesized using Naproxen as the synthetic precursor. The synthesized symmetrical chiral dimers were characterized by 1H NMR spectroscopy, and their liquid crystalline behavior was confirmed by DSC and HOPM studies. Structural effects on the mesomorphic and physicochemical properties were investigated in terms of variation of chiral chain length. The synthesized dimeric compounds exhibited SmX*, SmC*, SmA*, N*, BPI*, and BPII* mesophase sequences. An odd-even effect was observed in the dimers and the duration of the mesophase decreased with increasing spacer length. The synthesized vinyl substituted liquid crystalline dimers are particularly useful in understanding liquid crystal polymorphism and act as model compounds for liquid crystal polymers.

Chain Length Dependence of the Photovoltaic Properties of Monodisperse Donor–Acceptor Oligomers as Model Compounds of Polydisperse Low Band Gap Polymers

Well‐defined conjugated oligomers (Sn) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings (S1) are synthesized by a bottom‐up approach. UV–Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO–LUMO gap (ΔE) to values slightly smaller than that of the parent polymer (P1). Plots of ΔE and of the band gap of films (E g) versus the reciprocal chain length show that ΔE and E g converge towards a limit corresponding to an effective conjugation length (ECL) of 7–8 S1 units. UV–Vis absorption and photoluminescence data of solutions and solid films show that chain extension enhances the propensity to inter‐chain aggregation. This conclusion is confirmed by GIXD analyses which reveal that the edge‐on orientation of short‐chain systems evolves toward a face‐on orientation as chain length increases while the π‐stacking distance decreases beyond 7 units. The results obtained on solution‐processed BHJ solar cells show a progressive improvement of power conversion efficiency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/polydispersity and chain aggregation.

Chemical degradation of fluorosulfonamide fuel cell membrane polymer model compounds

The durability of a polymer electrolyte fuel cell membrane, along with high proton conductivity and mechanical performance is critical to the success of these energy conversion devices. Extending our work in perfluorinated membrane stability, aromatic trifluoromethyl sulfonamide model compounds were prepared, and their oxidative degradation was examined. The chemical structures for the models were based on mono-, di- and tri-perfluorinated sulfonamide modified phenyl rings. Durability of the model compounds was evaluated by exposure to hydroxyl radicals generated using Fenton reagent and UV irradiation of hydrogen peroxide. LC–MS results for the mono-substituted model compound indicate greater stability to radical oxidation than the di-substituted species; loss of perfluorinated fonamide side chains appears to be an important pathway, along with dimerization and aromatic ring hydroxylation. The tri-substituted model compound also shows loss of side chains, with the mono-substituted compound being a major oxidation product, along with a limited amount of hydroxylation and dimerization of the starting material.

Conjugated Polymers: Evaluating DFT Methods for More Accurate Orbital Energy Modeling

Density functional theory (DFT) calculations are useful to model orbital energies of conjugated polymers, yet discrepancy between theory and experiment exist. Here we evaluate a series of relatively straightforward calculation methods using the standard Gaussian 09 software package. Five calculations were performed on 22 different conjugated polymer model compounds at the B3LYP and CAM-B3LYP levels of theory and results compared with experiment. Chain length saturation occurs at approximately 6 and 4 repeat units for homo- and donor–acceptor type conjugated polymers, respectively. The frontier orbital energies are better approximated using B3LYP than CAM-B3LYP, and the HOMO energy can be reasonably correlated with experiment [mean signed error (MSE) = 0.22 eV]. The LUMO energies, however are poorly correlated (MSE = 0.59 eV), and we show that the molecular orbital energy of the triplet state gives a much better estimate of the experimentally determined LUMO level (MSE = −0.13 eV).

Oligofluorenes as Polymeric Model Compounds for Providing Insight into the Triplets of Ketone and Ketylimine Derivatives

A series of oligofluorenes ranging between one and three repeating units were prepared as structurally well-defined representative models of polyfluorenes. The photophysics of the oligofluorene models were investigated both by laser flash photolysis and steady-state fluorescence. The effects of the ketone and ketylimine functional groups in the 9-position on the photophysical properties, notably the triplet quantum yield (Φ(TT)) by intersystem crossing and the absolute fluorescence quantum yields (Φ(fl)), were investigated. The singlet depletion method was used to determine both the Φ(TT) and molar absorption coefficients of the observed triplets (ε(TT)). Meanwhile, the absolute Φ(fl) were determined using an integrating sphere. It was found that both the ketone and ketylimine substituents and the degree of oligomerization contributed to quenching the oligofluorene fluorescence. For example, the Φ(fl) was quenched 5-fold with the ketylimine and ketone substituents for the bifluorenyl derivatives compared to their corresponding 9,9-dihexyl bifluorenyl counterparts. Meanwhile, the Φ(fl) quenching increased 14 times with the trifluorenyl ketone and ketylimine derivatives. Measured Φ(TT) values ranged between 22 and 43% for the difluorenyl derivatives with ε(TT) on the order of 13 000 cm(-1) M(-1). The Φ(TT) decreased to <10% concomitant with doubling of the ε(TT) when the degree of oligomerization was increased to 3. A new fluorescence emission at 545 nm formed at low temperatures for the ketone and ketylimine oligofluorene derivatives. The emission intensity was dependent on the temperature, and it disappeared at room temperature.

Complexation of amidated pectin with poly(itaconic acid) as a polycarboxylic polymer model compound

Complexes based on amidated pectin (AP) and poly(itaconic acid) (PIA) were prepared by casting films from solutions of AP and PIA in different ratios with the pectin amount ranging from 10% to 90% by mass. The complexes were investigated by elemental analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG). In all investigated ratios of AP/PIA glassy transparent films with a uniform structure were obtained. The results of elemental analysis confirmed the composition of the complexes, and FTIR spectroscopy has shown carboxylic and amide peak shifting, indicating complex formation between AP and PIA. Comparison of thermograms of AP/PIA films with different ratios of AP indicated that the increase of the amount of AP increases the thermal stability of the films by retarding the onset of the main degradation processes.

Self-Assembly of Oligothiophene Chromophores by m-Calix[3]amide Scaffold

m-Calix[3]amides carrying the bithiophene chromophore (BTC3A) and terthiophene chromophore (TTC3A) were synthesized by the cyclic trimerization of m-aminobenzoic acid esters for the purpose of the control and understanding of the self-assembly of oligothiophene chromophores. Polymers and model compounds were also prepared for comparison. From the (1)H NMR experiments, cyclic trimer BTC3A showed the syn/anti equilibrium in solution, and the syn/anti conformer ratio (76/24 in CDCl(3)) was influenced by the solvent character. Namely, the population of the syn conformer was lowest (70%) in THF-d(8) and was highest (86%) in CDCl(3)/CD(3)OD (1/1 in volume). On the other hand, the population of the syn conformer of cyclic trimer TTC3A was high (84%) even in CDCl(3). In a CHCl(3) solution of cyclic trimer BTC3A, the absorption maximum (342 nm) blue-shifted and the emission maximum (448 nm) red-shifted compared with those of polymer BTPA and model compound BTM. The solvent character also had an impact on the optical properties of cyclic trimer BTC3A. The red-shifted emission maximum (481 nm) of cyclic trimer BTC3A in CH(3)OH indicated the interaction between three bithiophene chromophores. The emission maxima of cyclic trimer TTC3A (486 nm) demonstrated a small red-shift from model compound TTM (477 nm), and no solvent dependency was observed, unlike cyclic trimer BTC3A.

Reaction of SO4˙− with an oligomer of poly(sodium styrene sulfonate). Probing the mechanism of damage to fuel cell membranes

Clarification of the mechanism of degradation of model compounds for polymers used in polymer electrolyte fuel cells may identify intermediates that propagate damage; such knowledge can be used to improve the lifetime of fuel cell membranes, a central issue to continued progress in fuel cell technology. In proton-exchange membranes based on poly(styrene sulfonic acid), hydroxycyclohexadienyl radicals are formed after reaction with HO˙ and thought to decay to short-lived radical cations at low pH. To clarify subsequent reactions, we generated radical cations by reaction of SO(4)˙(-) with oligomers of poly(styrene sulfonic acid) (MW ≈ 1100 Da). At 295 K, this reaction proceeds with k = (4.5 ± 0.6) × 10(8) M(-1) s(-1), both at pH 2.4 and 3.4, and yields benzyl radicals with an estimated yield of ≤60% relative to [SO(4)˙(-)]. The radical cation is too short-lived to be observed: based on a benzyl radical yield of 60%, a lower limit of k > 6.8 × 10(5) s(-1) for the intramolecular transformation of the aromatic radical cation of the oligomer to a benzyl radical is deduced. Our results show that formation of the benzyl radical, an important precursor in the breakdown of the polymer, is irreversible.

Application of TOF‐SIMS to the direct determination of syringyl to guaiacyl (S/G) ratio of lignin

AbstractThe lignin syringyl to guaiacyl (S/G) ratio, the composition of monomeric units, is an important parameter that is widely used to obtain information on the complex polymer structure of lignin present in plant cell walls. We assessed the reliability of time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) for determining the S/G ratio using monomer, dimer and polymer model compounds of lignin. In the case of the monomer and dimer, the S/G ratios were much higher than the actual molar S/G ratios. In contrast, for the aryl ether 8‐O‐4′‐linked polymers, the S/G ratios estimated were similar to the actual S/G molar ratios, suggesting that the ionization efficiencies of the characteristic ions of S and G units detected from the synthetic lignin polymer compounds were similar. The results suggest that TOF‐SIMS is useful for rapid and convenient determination of the lignin S/G ratio in plants. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Synthesis of Bis(phenazasiline) Compounds and Their Application for TFT as a Model of Phenazasiline-Containing Polymers

Abstract New bis(phenazasiline) compounds were prepared and a thin film transistor (TFT) device containing bis(phenazasiline) derivatives was fabricated. The bis(phenazasiline)s, prepared from 2-bromo-8-methylphenazasiline, were effective materials for TFT. Obtained bis(phenazasiline) derivatives were considered to be model compounds of phenazasiline-containing polymers in the prediction of TFT properties.

Chemical Degradation of Membrane Polymer Model Compounds under Simulated Fuel Cell Conditions

Peroxide radical degradation is widely accepted as one of the key mechanisms by which PEM fuel cell membranes are eroded and ultimately fail. Testing of the mechanism of such failures is difficult, given the intractable nature of typical PEM polymers, and the low levels of degradation necessary to bring about failure. By use of low molecular weight model compounds, the mechanism of chemical degradation of both perfluorinated and hydrocarbon-based membranes can be simulated. These tests tell a clear story that common organic chemical reactivity patterns are followed, both polymer backbone carboxylic acid groups and side chain ether linkages are weak in perfluoro PEM materials, and that aromatic groups can be hydroxylated, and ether groups cleaved in hydrocarbon systems.

Chemical Degradation of Membrane Polymer Model Compounds under Similated Fuel Cell Conditions

not Available.

ChemInform Abstract: NEXAFS Spectromicroscopy of Polymers: Overview and Quantitative Analysis of Polyurethane Polymers

Abstract The successful application of X-ray spectromicroscopy to chemical analysis of polymers is reviewed and a detailed application to quantitative analysis of polyurethanes is presented. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is the basis of chemical sensitive X-ray imaging, as well as qualitative and quantitative micro-spectroscopy. These capabilities are demonstrated by a review of recent work, and by presentation of new results outlining a methodology for quantitative speciation of polyurethane polymers. C 1s inner-shell excitation spectra of a series of molecular and polymeric model compounds, recorded by gas phase inelastic electron scattering (ISEELS) and solid phase NEXAFS techniques, are used to understand the spectroscopic basis for chemical analysis of polyurethanes. These model species contain the aromatic urea, aromatic urethane (carbamate) and aliphatic ether functionalities that are the main constituents of polyurethane polymers. Ab initio calculations of several of the model molecular compounds are used to support spectral assignments and give insight into the origin and relative intensities of characteristic spectral features. The model polymer spectra provide reference standards for qualitative identification and quantitative analysis of polyurethane polymers. The chemical compositions of three polyurethane test polymers with systematic variation in urea/urethane content are measured using the spectra of model toluene diisocyanate (TDI) urea, TDI-carbamate, and poly(propylene oxide) polymers as reference standards.

Thermal Analysis of Model Compounds of Polymers

Thermal Analysis of Model Compounds of Polymers