Phenyl End Groups Research Articles

Improving chitosan performance in the simultaneous adsorption of multiple polycyclic aromatic hydrocarbons by oligo(β-pinene) incorporation

The occurrence of persistent organic pollutants in aquatic bodies, namely polycyclic aromatic hydrocarbons (PAHs), has been increasingly detected. The presence of such contaminants represents a serious threat to human health due to their toxicity. Therefore, aiming to provide a novel and efficient alternative for PAHs' removal from water, the present study assesses the effect of oligo(β-pinene) blended with chitosan for the adsorption of these pollutants. Oligo(β-pinene) with phenyl end-groups was synthesized by organocatalyzed atom transfer radical polymerization (O-ATRP) and incorporated in different concentrations (6, 12, and 18 %) to chitosan films. The oligo(β-pinene) loading in the chitosan matrix impressively improved this polysaccharide adsorption capacity. The formulation containing 12 % of oligomer demonstrated a contaminant removal performance three times higher (298.82 %) than pure chitosan during only 1 h of the decontamination process. Adsorption isotherms showed an improved uptake of PAHs with the increase of the contaminants' concentration in the aqueous media due to the formation of a higher concentration gradient. Additionally, a comprehensive characterization of oligo(β-pinene)/chitosan formulation was performed to provide a better understanding of the interactions between the components of the blends. Overall, it was concluded that oligo(β-pinene)/chitosan blends can be used as a high-performance and sustainable alternative for PAHs removal.

On the road to stable, isolable [4]cumulenes: Reactivity and cyclization reactions

AbstractThe design and synthesis of persistent tetraaryl[4]cumulenes are reported. Derivatives with phenyl endgroups ([4]Ph and [4]Ph/Ar*) are susceptible to reactions during synthesis and/or purification that complicate isolation of the desired product, particularly intermolecular dimerization reactions. Incorporation of (3,5‐di‐tert‐butyl)phenyl endgroups (Ar*) provides increased stability, culminating in the stable and isolable [4]cumulene [4]Ar*. Cumulene [4]Ar* remains, however, susceptible to dimerization under pressing conditions, and [4]Ar* also readily reacts with electrophiles under mild conditions that lead to intramolecular cyclization. Given the structural complexity of the side products in these studies (compounds 3, 10, 14, 17, 18), X‐ray crystallography plays a vital role in their identification.

The Effect of End Group and Molecular Weight on the Yellowness of Polyetherimide

The effects of end group and molecular weight on the yellowness of telechelic polyetherimide (PEI) are investigated. Electron-withdrawing dianhydride end groups reduce the yellowness and increase the transparency of PEI regardless of the molecular weight. Electron-donating phenyl, amine, and phthalic end groups increase the yellowness of PEI but the effect depends on the molecular weight. As the molecular weight is increased, the yellowness of PEIs with electron-donating end groups initially decreases due to a decreasing end-group density and then increases due to an increasing probability of charge-transfer complex formation. The systematic study reveals the correlations among yellowness, end group, and molecular weight of PEIs. The correlations can be used for designing highly transparent PEIs and other high-performance polymers.

Synthesis, electrolyte properties and solar cell performance of hyperbranched poly(aryl-ether-urea)s

ABSTRACTHyperbranched poly(aryl-ether-urea)s with phenyl, N,N-dimethylamino ethyl and polyethylene oxide end-groups linked through urethane group – HBPEU-1, HBPEU-2 and HBPEU-3 respectively – were synthesized from an AB2-type blocked isocyanate monomer and characterized by FT-IR, 1H-NMR, SEC-MALLS, TGA and DSC techniques. The molecular weight of the polymers were found to be ranged from 4.9 × 103 − 1.96 × 104 g/mol. The TGA results showed that the polymers decompose between 175°C – 220°C. In the DSC curves, HBPEU-1 and HBPEU-3 showed Tg at 160°C and 53°C respectively, whereas HBPEU-2 did not showed clear Tg. All the three polymers were converted into polymer electrolytes by doping with LiI/I2. The doped polymers showed remarkably high ionic conductivity, up to 222 – 277 times compared to the un-doped polymers and the highest conductivity was observed with doped HBPEU-2. The TiO2 based dye-sensitized solar cells (DSSCs) were fabricated using the doped polymer electrolytes and their performance was tested; HBPEU-2 showed good performance by yielding energy conversion efficiency (η) of 4.5%.

Impact of Energetically Engineered Dielectrics on Charge Transport in Vacuum-Deposited Bis(triisopropylsilylethynyl)pentacene

The surface functionality of the gate dielectrics is one of the important variables to have a huge impact on the electrical performance of organic field-effect transistors (OFETs). Here, we describe the impact of energetically engineered dielectrics on charge transport in vacuum-deposited 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) thin films for eventually realizing high-performance OFETs. A variety of self-assembled monolayers (SAMs) bearing amino, methyl, phenyl (PTS), or fluoro end groups were introduced onto the SiO2 dielectric surfaces to design energetically engineered surfaces that can be used to explore the impact of surface functionalities at a TIPS-pentacene/gate dielectric interface. The solvent-free vacuum deposition of TIPS-pentacene was used to exclude solution-processing effects resulting from fluid flows and solvent drying processes. The TIPS-pentacene layer on the PTS-SAM yielded the best morphological and crystalline structures, which directly enhanced the electrical pr...

Synthesis of Well-Defined Oligo(2,5-dialkoxy-1,4-phenylene vinylene)s with Chiral End Groups: Unique Helical Aggregations Induced by the Chiral Chain Ends.

Oligo(2,5-dialkoxy-1,4-phenylenevinylene)s containing three different chiral alkoxy substituents on the phenyl end groups with structurally regular (all trans) controlled repeat units have been prepared; these compounds showed highly enhanced aggregation-induced circular dichroism (AICD; formation of supramolecular polymers), and an inversion of the CD signal was observed even with the same end groups under certain conditions.

Effect of hybrid nanoparticles on glass transition temperature of polymer nanocomposites

Changes in the glass transition temperatures of composites based on polystyrene and nanosized macromolecular nanostructures (molecular silicasols, dendrimers) are reported. Silicasols are nanosized particles consisting of a silica core and an ethyl phenyl shell; dendrimers are formed using a carbosilane core with ethyl phenyl end groups. It has been observed that the glass transition temperatures of the composites (Tgc) may be either above or below the glass transition temperature of polystyrene, depending on the size of the filler particles. A theoretical model based on the relation between the glass transition temperature and the configurational entropy of the composite, which satisfactorily describes the experimental dependence, was developed. It is found that the effect of the size of the hybrid nanoparticles on Tgc was determined using two factors. First, the presence of an organic layer on the surface of nanoparticles increases the number of degrees of freedom and the entropy of the system, thereby reducing Tgc. Second, the particles present in the polymer reduce the number of configuration states of macromolecules, which reduces the disorientation entropy. This effect leads to an increase Tgc. The competition between these two main factors determines the sign of the glass transition temperature deviation. The size of the particles and their organic surface layer play the key roles in the thermodynamic properties of the composites. POLYM. COMPOS., 37:1978–1990, 2016. © 2015 Society of Plastics Engineers

Spectral dependence of nonlinear optical properties of symmetrical octatetraynes with p-substituted phenyl end-groups.

Organic compounds containing conjugated carbon chains have been extensively investigated due to their interesting properties including nonlinear optical response. Polyynes are a group of compounds where the conjugation can be modified by appropriate selection of end-groups, enabling "control" and improvement of nonlinear effects. In this work, we investigate three newly synthesized aryl end-capped octatetraynes, exhibiting strong nonlinear absorption and nonlinear refraction properties, which can be attributed to the presence of aryl end-groups with electron-withdrawing functional groups suitable for further extending the conjugation. Nonlinear optical measurements were performed using a f-scan (modified Z-scan) technique with a femtosecond laser system at various wavelengths in the visible and near-infrared range (540-1600 nm), revealing strong negative third-order nonlinear refraction (3NR) and two-photon absorption (2PA) below 600 nm and a noticeable three-photon absorption (3PA) at longer wavelengths. The results of spectroscopic characterization and the crystallographic data for the investigated compounds are also presented.

Self-Ordering Properties of Functionalized Acenes for Annealing-Free Organic Thin Film Transistors

Presented here is a study of the molecular self-ordering properties of four bis(phenylethynyl) anthracene based organic semiconductors related to their electronic structure employing X-ray spectroscopy techniques and density functional theory (DFT) calculations. The local molecular order through polarization dependence of C 1s → π* transitions revealed ordered π-stacking nearly perpendicular to the substrate due to van der Waals interactions between alkyl groups. DFT calculations were used to deconvolute the measured electronic structure and examine effects of small changes in molecular geometry in relation to measured charge carrier mobility in top contact field effect transistors. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are found to be conjugated from the anthracene core across the bridging ethynyl groups to the thiophene and phenyl end groups. The inclusion of ethynyl bridges connecting the thiophenes has a twofold effect of both reducing the rotational freedom of this functional group and increasing HOMO/LUMO conjugation across the molecules. These features help create a more rigid upright structure for HB-ant-THT with better molecular orbital conjugation and subsequent higher mobility. With this understanding of how different functional groups interact with an acene core, future synthesis of new materials may be directed toward annealing-free organic semiconducting materials.

A study on threshold voltage stability of low operating voltage organic thin-film transistors

A low operating voltage (<2 V) organic field-effect transistor (OFET) using phenylhexyltrichlorosilane (PTS) self-assembled monolayer (SAM) dielectric and copper phthalocyanine (CuPc) as semiconductor with improved mobility (0.035 cm2 V−1 s−1) and threshold voltage stability was demonstrated. This device showed better performance when compared to an OFET with octyltrichlorosilane (OTS-8) SAM dielectric. The improved mobility was attributed to the 2D growth mode of CuPc on PTS SAM because of surface energy matching between the two, whereas CuPc film on OTS-8 showed a 3D growth mode with larger grain boundary density. The higher threshold voltage stability of OFETs on PTS SAM was attributed to the efficient coverage and screening of trap centres at dielectric/semiconductor interface due to stronger intermolecular linking and formation of closely packed surface by the bulky phenyl end groups. Decrease in grain boundaries offered by 2D growth of CuPc for electron and hole trapping was also found to be another reason for improved threshold voltage stability. The results indicated that the nature of the end group of SAM dielectric, surface chemistry of dielectric and initial growth mode of semiconductors are all responsible for improvement in threshold voltage stability and enhanced performance of OFET.

Crystallisation of the orthorhombic form of acetaminophen: Combined effect of surface topography and chemistry

Abstract A new method for the crystallisation of the metastable orthorhombic polymorph of acetaminophen using colloidal templates with specific surface topographies and surface chemistry is reported in this study. The templates were prepared from silica nanoparticles (220 nm) and their surface chemistry was modified by in situ silanisation using different organo-silanes to attach amino, phenyl, dodecyl and trifluoropropyl functional end groups. Cooling crystallisation was performed on the surfaces of novel colloidal templates using a simple single step rapid cooling method, which resulted in selective crystallisation of the metastable orthorhombic form on the surfaces with a specific surface topography and surface functional end groups in conditions, which typically yielded monoclinic crystal forms. Here, we report crystallisation of the orthorhombic form of acetaminophen at super-saturation c/csat = 1.5, which is lower as compared to the c/csat = 2.0 reported in the literature. The method reported here has shown potential for surface selective polymorphic control of organic molecules using combined effect of surface topography and surface chemistry.

Crystal structure of complexes of pentavalent neptunium with 1,8-bis[2-(diphenylphosphinylmethyl)]phenoxy-3,6-dioxaoctane (L) and hexavalent actinides (U, Np, Pu) with 1,8-bis[2-(diphenylphosphinyl)]phenoxy-3,6-dioxaoctane (L1)

Complexes of pentaand hexavalent actinides with phosphoryl-containing podands incorporating a triethylene glycol fragment and 2-(diphenylphosphinyl)phenyl (L1) or 2-(diphenylphosphinylmethyl)phenyl (L) end groups were synthesized and structurally characterized. The complexes can be described by the following formulas: [NpO2L(C2H5OH)(NO3)] (I) for pentavalent neptunium and [AnO2(L1)2](OH)2 · nH2O (II), where An is U (IIa), Np (IIb), and Pu (IIc), for the isostructural compounds of hexavalent actinides. In I, L is a bidentate bridging ligand. The Np5+ coordination polyhedron is a pentagonal bipyramid. The bipyramid equatorial plane is formed by the oxygen atoms of two podands L, the bidentate nitrate ion, and the ethanol OH group. The oxygen atoms of the phosphoryl groups of the podand are involved in the coordination environment of two NpO2+ cations where they connect the electrically neutral neptunoyl nitrate fragments to infinite chains along the [100] direction, which are in turn connected into ribbons by strong hydrogen bonds. The crystal of II consists of the complex cations [AnO2(L1)2]2+, hydroxyl ions, and water molecules of crystallization. The environment of AnO22+ is formed by four ligands L1 whose oxygen atoms form a tetragonal-bipyramidal coordination environment. Each of the two crystallographically independent ligands L1 is connected to two AnO2+ cations. This gives positively charged layers of actinyl cations perpendicular to the [010] direction connected by molecular ligands. The layers contain channels accommodating hydroxyl ions and crystallization water molecules.

MALDI-TOF/TOF CID Study of Poly(p-phenylene sulfide) Fragmentation Reactions

A study involving the evaporation−grinding MALDI sample preparation method, MALDI-TOF/TOF CID, and Py-GC/MS is presented to examine the fragmentation mechanisms of poly(p-phenylene sulfide) (PPS). MALDI-TOF/TOF CID fragmentation studies yielded a wealth of information about the mass, structure (linear or cyclic), end-groups, and backbone modifications of the polymer. Additionally, Py-GC/MS experimental data are presented for comparison of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS.(1, 2) TOF/TOF CID results indicate that linear PPS undergoes random main chain fragmentation along the polymer backbone and preferentially fragments at bonds adjacent to dibenzothiophene and phenyl end-groups. Cyclic species produce fragment ions similar to linear species. However, the MS/MS precursor ions for cyclic PPS are, by far, the most intense peaks, while the precursor ions for linear species show relatively low intensity. CID fragmentation results are supported by Py-GC/MS data and are consistent with the proposed degradation mechanisms.

Supramolecular assembly of one-dimensional channels and two-dimensional brick-wall networks from asymmetric dithioether ligands and copper(I) iodide

Two asymmetric dithioether ligands with cyclohexyl (L1) and phenyl (L2) end-groups were synthesized. Reaction of L1 with copper(I) iodide afforded a 1D channel-type coordination polymer {[Cu4I4(L1)2](CH3CN)0.5}n (1) interconnected by cubane-type tetranuclear Cu4I4 cluster units. Whereas, a 2D brick-wall-type coordination polymer [CuI(L2)]n (2) with rhomboid dinuclear Cu–I2–Cu nodes was isolated from the reaction of L2 with copper(I) iodide.

Grafting Polymerization of Acrylonitrile onto LDPE Film: Study on Grafting Chain Length and Density with UV-vis Spectroscopy

Grafting polymerization of acrylonitrile onto low density polyethylene film was studied further following the earlier work [1]. A novel and effective method was developed to directly determine the number of end-groups, i.e. phenyls at the end of grafted chains with UV-vis spectroscopy; according to the number of phenyl end-groups and the weight of grafted polymers, grafting chain length and density were estimated; investigations indicated both of these two parameters could be practically controlled.

Influence of structural factors on degradation product formation: Primary pyrolysis products of poly(acyl sulfides) investigated by direct pyrolysis mass spectrometry

Thermal degradation of two poly(acyl sulfide) polymers, poly(adipoyl sulfide) (PADS) and poly(terephthaloyl sulfide) (PTS) was investigated by direct pyrolysis mass spectrometry (DPMS). The structures of pyrolysis products detected in the DPMS analysis of both PADS and PTS indicate that the thermal degradation takes place mainly through a loss of carbon monoxide and carbonyl oxysulfide leading to the formation of cyclics. In the case of PADS, linear products with thioacid end groups were formed through hydrogen transfer reactions. In the case of PTS, almost equal proportions of linear products with phenyl end groups and cyclic products were formed. The mechanism of formation of degradation products has also been addressed.

Monolayers of Diphenyldiacetylene Derivatives: Tuning Molecular Tilt Angles and Photopolymerization Efficiency via Electrodeposited Ag Interlayer on Au

An electrodeposited Ag adlayer (upd, underpotential deposition) is utilized to improve monolayer photopolymerization of diphenyldiacetylene derivatives (DPDAs) that would otherwise exhibit no polymerization in solid state. Topochemical reaction of diacetylene derivatives via solid-state 1,4-addition yields polydiacetylenes which are of great importance due to properties associated with their ene-yne conjugated backbones. The polymerization efficiency heavily depends on the molecular arrangement in the crystals. For example, crystals of most DPDA derivatives show no activity for topochemical reaction because the bulky phenyl end groups space out the triple bonds and thus DPDAs require relatively large translation and rotation angles for polymerization. In principle, topochemical reaction is viable if molecules are in optimal arrangement. The upd interlayer can be applied to tune the adsorbate-substrate interactions, intermolecular spacing, and the molecular tilt angle by controlling the coverage of the Ag adlayer. It is thus possible to manipulate the molecular arrangement of DPDAs for the subsequent polymerization. Successful photopolymerization of DPDA monolayers is realized from the decrease in nu(C[triple bond]C) intensity by infrared reflectance absorbance spectroscopy, growth of ene-yne pi-pi* transition by UV-vis measurements, and enhanced electrochemical stability by the cathodic desorption protocol. The optimal efficiency of polymerization takes place on upd-modified substrates that can generate approximately 45 degrees tilt angle for DPDA derivatives.

Effect of supercritical carbon dioxide on the diffusion coefficient of phenol in poly(bisphenol A carbonate)

AbstractFor some polymers, the rate of solid‐state polymerization (SSP) is higher with supercritical carbon dioxide (scCO2) as the sweep gas than with atmospheric N2. One explanation for this higher rate is that the diffusion coefficient of the condensate molecule is higher in the CO2‐swollen polymer. To investigate this hypothesis, we measured the diffusion coefficient of phenol in poly(bisphenol A carbonate) (BPA‐PC) by carrying out SSP of this polymer under diffusion‐limited conditions. Under these conditions, the diffusion coefficient of the condensate molecule could be calculated from the profile of the molecular weight versus time. The phenol diffusivity was determined between 135 and 180 °C in the presence of N2 at about 1 bar and in the presence of scCO2 at about 138, 207, and 345 bar. The diffusion coefficient of phenol was up to 200% higher in scCO2 than in N2, depending on the temperature and CO2 pressure. With both N2 and scCO2, the activation energy for phenol diffusion in BPA‐PC was larger than the activation energy for the reaction between hydroxyl and phenyl end groups that occurred during SSP of BPA‐PC. As a result, the overall SSP reaction shifted from diffusion control at low temperatures toward chemical‐reaction control at high temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1143–1156, 2003

End-group analysis of blue light-emitting polymers using matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry.

An analytical method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been applied to provide information on the structure of a copolymer, e.g., repeat unit and end group. Seven conjugated polymers, which have been demonstrated as the active component in blue light-emitting diodes, were synthesized through Suzuki polycondensation reaction in the presence of Pd(PPh3)4 catalyst. Their molecular weights were obtained using gel permeation chromatography analysis. MALDI-TOF MS was used to investigate the structure information in detail. The proposed end-group structures were confirmed by the identity between the observed and the simulated isotopic distribution of each polymer. The results demonstrate that these synthetic polymers possess various end groups and even contain macrocycles. The catalyst Pd(PPh3)4 was found to introduce phenyl end groups via aryl-aryl exchange between the catalytic palladium intermediate and the triphenylphosphine ligand. All these results are based on the analysis of the mass spectrum data, which suggests that MALDI-TOF MS is an extraordinarily strong tool in synthetic polymer structure analysis.

Distribution of End Groups within a Dendritic Structure: A SANS Study Including Contrast Variation

We present an analysis of the distribution of end groups within a urea-functionalized poly(propyleneamine) dendrimer of the fourth generation by small-angle neutron scattering (SANS). The phenyl end groups have been deuterated to enhance their contrast. The SANS experiments are performed using solution of the labeled dendrimer in mixtures of protonated and deuterated dimethylacetamide (DMA). In this way the contrast between the solute and the solvent is varied in a systematic fashion (contrast variation). The analysis presented here gives three partial scattering functions that depend differently on contrast. From these data, the scattering length density within the dendritic structure can be derived. All results show that the end groups are dispersed throughout the dendrimer with a broad maximum located at a radial distance that corresponds to ca. half of the overall size of the molecule. Hence, there is no well-defined surface of a dendritic structure defined by the end groups, but the end groups are mo...