Methoxy End Groups Research Articles

Analysis of rapid chain dynamics in isochronal dielectric measurements of polymers

Fast dynamics within the microwave frequency range (approximately gigahertz) in polymer systems as a function of temperature (in the range from 20 to 190 degrees C) were studied using high frequency dielectric spectroscopy. The frequency of radiation was varied from 0.5 to 18 GHz. The isochronal dielectric loss data were taken to eliminate the complexity arising from the frequency-independent, temperature-dependent background loss in the condensed phase. These studies were conducted for poly(caprolactone) (PCL), poly(ethylene oxide) (PEO), poly(ethylene oxide) with methoxy end group (PEO-CH3), PLA-b-PEO-b-PLA triblock copolymers, and several polymers with high glass transition temperatures. These polymers possess glass temperatures ranging from -62 degrees C (PCL) to 110 degrees C (PMMA). One broad relaxation process was found only for polymers (PCL, PEO, and PLA-b-PEO-b-PLA) with low glass transition temperatures. The effect due to end groups was investigated by comparing the results of PEO with hydroxy versus methoxy end groups. The measured relaxation process was determined not to be associated with end groups. The results from temperature-dependent dielectric spectroscopy indicate that the relaxation process follows an Arrhenius T dependence suggesting that it is due to local motions. The activation energy of the relaxation process was measured and investigated based on the coupling model. The results suggest that the observed relaxation process behaves as a Johari-Goldstein beta relaxation.

Synthesis and characterization of azo‐based methacrylate polymers with methoxy and nitro end groups for nonlinear optical applications

AbstractOne new and three already described azobased methacrylate monomers with methoxy and nitro end groups and spacer length 2 and 6 were synthesized. These monomers were copolymerized with methyl methacrylate and the monomers as well as copolymers were characterized by classical spectroscopy techniques (FTIR, NMR, and UV‐VIS), gel permeation chromatography (GPC), elemental analysis and thermal analysis (TGA and DSC). The glass transition temperature of the polymers was found to be above room temperature and thermal decomposition temperatures above 100°C. All the polymers were amorphous in nature and formed excellent homogeneous films with good optical transparency. The polymer films coated on indium tin oxide glass slides were poled and their order parameters were calculated to check the stability of oriented dipoles. Few samples were also studied for their second harmonic generation properties. Temporal stability, checked up to 120 h at room temperature, was found to be quite satisfactory. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3497–3504, 2007

A molecular dynamics study of ion-conduction mechanisms in crystalline low-Mw LiPF6·PEO6

Molecular dynamics (MD) simulation has been used to probe ion-conduction mechanisms in crystalline LiPF6·PEO6 for smectic- and nematic-ordered models of methyl-terminated short-chain monodisperse poly(ethylene oxide) chains with the formula CH3–(OCH2CH2)23–OCH3; Mw = 1059. The effect of aliovalent substitution of the PF6− anion by ca. 1% SiF62− has also been studied. External electric fields in the range 3–6 × 106 V m−1 have been imposed along, and perpendicular to, the chain direction in an effort to promote ion transport during the short time-span of the simulation. Ion-migration barriers along the polymer channel are lower for the nematic models than for the smectic, with anions migrating along the channels more readily than Li-ions. Ion mobility within the smectic interface could also be confirmed, but at a higher field-strength threshold than along the chain direction. Li-ion migration within the smectic plane appears to be suppressed by ion pairing, while Li-ion transport across the smectic gap is facilitated by uncoordinated methoxy end-groups. Interstitial Li-ions introduced into the PEO channel through SiF62− doping are also shown to enhance Li-ion conduction.

Characterization of stationary phases for gas chromatography by 29Si nuclear magnetic resonance spectroscopy : III. Carborane–siloxane copolymers

Five bis(dimethylsilyl)- m-carborane–siloxane polymers with methyl, phenyl, and 2-cyanoethyl ligands were characterized by 1H, 11B, 13C, and 29Si nuclear magnetic resonance (NMR) spectroscopy. All relevant chemical shifts are reported, whereas signal assignment was confirmed by 2D NMR spectroscopy. The chemical composition of the polymers was calculated from the 1H and 29Si NMR spectra. Only 29Si NMR spectroscopy was able to quantify the methoxy end group, from which the average molecular weights were calculated. The copolymer Dexsil 300 turned out to have a regular microstructure, whilst the terpolymers Dexsil 400 and Dexsil 410 have only partly regular sequences. 11B NMR spectroscopy confirmed the m-carborane structure and revealed some low molecular weight impurities.

Effect of side‐chain end groups on the optical, electrochemical, and photovoltaic properties of side‐chain conjugated polythiophenes

AbstractThree new side‐chain conjugated polythiophene derivatives, poly{3‐[2‐(3‐methoxy‐4‐octyloxy‐phenyl)‐vinyl]‐thiophene} (P3MOPVT), poly{3‐[2‐(3,5‐dimethoxy‐4‐octyloxy‐phenyl)‐vinyl]‐thiophene} (P3DMOPVT), and poly{3‐[2‐(3,4‐dioctyloxy‐phenyl)‐vinyl]‐thiophene} (P3DOPVT), were synthesized by Wittig‐Hornor reaction and GRIM method and compared with poly{3‐[2‐(4‐octyloxy‐phenyl)‐vinyl]‐thiophene} (P3OPVT) for investigating the effect of the end groups of the conjugated side‐chain on the properties of the polymers. Owing to the electron‐donating ability of methoxy groups, the visible absorption peaks of P3MOPVT and P3DMOPVT solutions and films become stronger and red‐shifted compared with P3OPVT. The electrochemical bandgaps of the four polymers are 2.15 eV for P3OPVT, 1.99 eV for P3MOPVT, 1.85 eV for P3DMOPVT, and 2.36 eV for P3DOPVT, respectively, which indicate that the electron‐donating ability of the methoxy end group on the conjugated side chain of P3MOPVT and P3DMOPVT and the large steric hindrance of the two octyloxy end groups on the conjugated side chain of P3DOPVT have obvious influence on the electrochemical properties of the side‐chain conjugated polythiophenes. Polymer solar cells were fabricated with a structure of ITO/PEDOT:PSS/Polymer:PCBM/LiF/Al. The best device, based on P3DMOPVT, shows a power conversion efficiency of 1.63% under the illumination of AM1.5, 80 mW/cm2. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4916–4922, 2006

Hybrid polymer latexes—acrylics‐polyurethane: II. mechanical properties

AbstractPolyurethanes were prepared from reaction of isophorone diisocyanate (IPDI) with polypropylene glycol (PPG), with chain extension with butanediol (BDO). Their end groups are either methoxy, or methacrylic groups. These polyurethanes (PUs) are dissolved in mixtures of acrylic monomers (methylmethacrylate, MMA, and butylacrylate, BA). The solutions are sonicated to produce miniemulsion droplets, using sodium dodecyl sulfate (SDS) as surfactant, the PU being the hydrophobe. These miniemulsions were polymerized, with an oil‐soluble peroxide initiator. Those latexes with methoxy end groups in the PU are fully soluble, while those containing the acrylic end groups are almost fully crosslinked, but can easily form smooth films. The mechanical properties of these films were studied from their stress–strain curves, and compared with those films formed from the uncrosslinked hybrid latexes. Copyright © 2005 John Wiley & Sons, Ltd.

Materials selection guidelines for membranes that remove CO 2 from gas mixtures

Membrane technology has been investigated for removing CO 2 from mixtures with light gases such as CH 4, N 2 and H 2, and optimal membranes with high CO 2 permeability and high CO 2/light gas selectivity are of great interest. This overview describes the material science approaches to achieve high CO 2 solubility and CO 2/light gas solubility selectivity by introducing polar groups in polymers. CO 2 solubility and CO 2/N 2 solubility selectivity in both liquid solvents and solid polymers containing a variety of polar groups are discussed. Optimum materials appear to have a solubility parameter of about 21.8 MPa 0.5 to achieve both high solubility and high solubility selectivity. However, the introduction of polar groups can decrease CO 2 diffusion coefficients and can make a material more size-selective, which is detrimental to, for example, CO 2/H 2 separation properties. So far, ether oxygens in ethylene oxide (EO) units appear to provide a good balance of CO 2 separation and permeation properties. One drawback of using pure poly(ethylene oxide) (PEO) is its strong tendency to crystallize. This report reviews strategies for incorporating high concentrations of EO units into polymers while suppressing crystallization. A simple model, based on free volume theory, is used to correlate a wide range of CO 2 permeability coefficients in PEO containing materials, and the results are satisfactory, particularly given the simplicity of the model. Crosslinked poly(ethylene glycol) acrylate (XLPEO) containing branches with methoxy end groups exhibit the highest CO 2 permeability (i.e. 570 Barrers) and highest CO 2/H 2 selectivity (i.e. 12) at 35 °C and infinite dilution among all PEO containing materials reported to date. Because such materials do not crystallize at typically accessible temperatures, CO 2/H 2 selectivity can be further improved by decreasing temperature. For example, at an upstream pressure of 4.4 atm, CO 2/H 2 pure gas selectivity reaches a value of 40 at −20 °C while maintaining a CO 2 permeability of 52 Barrers.

Pegylated polystyrene particles as a model system for artificial cells.

Pegylated polystyrene particles (PS-PEG) were prepared as a model system for artificial cells, by modification of carboxyl polystyrene particles (PS-COOH) with homo- and hetero-bifunctional polyethylene glycols (PEG, MW 1500, 3400, and 5000) containing an amino end group for immobilization and an amino, hydroxyl, or methoxy end group that is exposed at the surface after immobilization. Protein adsorption from human plasma dilutions (85 v %) onto PS-PEG with a PEG surface concentration higher than 40 pmol/cm2 was reduced up to 90-95% compared with protein adsorption onto PS-COOH with a final protein surface concentration of approximately 30 ng/cm2. Two-dimensional gel electrophoresis analyses showed that 30% of the total amount of adsorbed proteins onto PS-PEG are dysopsonins (i.e., nonadhesive proteins like albumin and apolipoproteins). For PS-COOH, <15% of the amount of adsorbed proteins are dysopsonins. In addition, the generation of terminal complement compound (TCC) by PS-PEG particles with a PEG surface concentration lower than approximately 55 pmol/cm2 is not significant. The low protein adsorption, the relatively high percentage of adsorbed dysopsonins, and the low level of complement activation may prevent the uptake of PS-PEG by the mononuclear phagocytic system (MPS) in vivo. Moreover, PS-PEG (PEG surface concentration > approximately 35 pmol/cm2) shows minimal interaction with cultured human umbilical vein endothelial cells (HUVEC), which mimics the endothelial lining of the blood vessel wall.

Evidence for Two Chain Length Distributions in the Polymerization of Formaldehyde on Cu(100)

The polymer species formed from the spontaneous polymerization of formaldehyde (H2CO) on clean Cu(100) at 85 K were studied using electron energy loss spectroscopy (EELS) and temperature-programmed desorption (TPD). Formaldehyde forms poly(oxymethylene) (POM) with differing chain lengths; the long (α) and short (β) chain species depolymerize to give two features in TPD at approximately 207 and 219 K, respectively. The complex desorption kinetics observed for the α-POM species were successfully modeled using equations based on the ratio of the average number of monomers unzipped from the chain per initiation event to the length of the polymer chain. Losses were observed in EEL spectra of the short-chain species at ∼290, ∼1020, and ∼1120 cm-1 that can be assigned to the ν(Cu−O), ν(C−O), and ρ(CH3) modes of oxygen and methoxy endgroups, respectively. Preadsorbed methanol increases the proportion of short-chain POM species by increasing the probability of termination for the β species. Lower thermal stability for adsorbed POM was observed compared to bulk POM and is believed to be related to the stability of the surface-bound oxygen endgroup.

Voltammetry of electroactive liquid redox systems: anion insertion and chemical reactions in microdroplets of para -tetrakis(6-methoxyhexyl) phenylenediamine, para - and meta -tetrahexylphenylenediamine

The effect of the structure of the organic precursor molecule on the electroinsertion of anions and on the formation of materials in the ionic liquid state is compared for three compounds, para-N, N, N′, N′-tetrahexylphenylenediamine (p-THPD), meta-N, N, N′, N′-tetrahexylphenylene diamine (m-THPD), and para-N, N, N′, N′-tetrakis(6-methoxyhexyl)phenylenediamine (p-TMHPD), by characterising their condensed phase voltammetric properties in aqueous media. The electrochemically driven anion insertion in p-THPD and p-TMHPD in the presence of ClO4 −, F−, Cl−, Br−, I−, and SO4 2− is shown to be extremely sensitive to structure. The introduction of the methoxy end groups in p-TMHPD causes (1) a considerable shift to more negative electroinsertion potentials, (2) a less stable response which upon continuous cycling decreases, and (3) considerably lower anion selectivity. For the insertion of sulfate, only p-TMHPD yields an electrochemical response which is shown to be consistent with insertion of the dianion SO4 2−. The electrochemical oxidation of a deposit of m-THPD is accompanied by anion insertion and a chemical reaction step in an EC-type electrochemical process. The product of the chemical step is electrochemically active and results in a new reversible electroinsertion process. Starting materials and products of the microdroplet reactions are characterised by Maldi-TOF mass spectrometry and a reaction mechanism based on condensed phase polymerisation is proposed.

End Effects in Poly(styrene)/Poly(ethylene oxide) Copolymers

We have studied phase boundaries and critical scattering on equivalent systems of homopolymer blends and diblock copolymers with different end groups terminating the polymer chains. The aim is to investigate the effect of end groups relative to the effect of the covalent junction in diblock copolymers. Either effect intuitively causes corrections with a V-1 dependence on the molar volume V. Besides the experimental phase boundaries, the Flory−Huggins interaction parameter has been determined and is discussed. The polymer systems studied is based on poly(styrene), PS, and poly(ethylene oxide), PEO, where the latter polymer chain is terminated by either a hydroxy or a methoxy group. The change from hydroxy to methoxy end groups caused a change in the phase boundary of 90K and 45K for homopolymer blends (V̄ = 1970 cm3/mol) and diblock copolymers (V̄ = 17 700 cm3/mol), respectively.

Calixarenes as a new class of external electron donors in Ziegler–Natta polypropylene catalysts

In this work we have shown that calixarenes form a new type of external donor ligand which can function effectively as a selectivity control agent to increase the yield of isotactic polypropylene in late-generation Ziegler–Natta catalysts. The procatalyst prepared utilized dibutylphthalate as the internal donor to function with the calixarene. We have synthesized and characterized a wide variety of new substituted calixarenes containing hydroxy- and methoxy-end groups. All of these calixarenes were evaluated in the bulk polymerization of propylene and found to increase significantly the amount of i-PP formed relative to reactor runs performed without the calixarene.

Synthesis and phase behavior of side-chain liquid crystalline polymers with pendant quinoline rings bearing either a polar or a non-polar end group

Four methacrylate monomers, 2a–2d, containing a quinoline ring with a NO2 or a OCH3 group at the end of the mesogen were synthesized and polymerized. The copolymers with six methylene units as spacer, 3b–3d, showed a smectic phase induced by electron donor-acceptor interactions of the side groups. The homopolymer with eleven methylene units as spacer and methoxy end group, 3f, showed a smectic phase induced by the large length of the spacer. The copolymers with eleven methylene units, 3g–3i, showed a smectic phase induced by both the electron donor-acceptor interactions of the side groups and the large length of the spacer.

Synthesis and phase behavior of side-chain liquid crystalline polymers with pendant quinoline rings bearing either a polar or a non-polar end group

Four methacrylate monomers, 2a–2d, containing a quinoline ring with a NO2 or a OCH3 group at the end of the mesogen were synthesized and polymerized. The copolymers with six methylene units as spacer, 3b–3d, showed a smectic phase induced by electron donor-acceptor interactions of the side groups. The homopolymer with eleven methylene units as spacer and methoxy end group, 3f, showed a smectic phase induced by the large length of the spacer. The copolymers with eleven methylene units, 3g–3i, showed a smectic phase induced by both the electron donor-acceptor interactions of the side groups and the large length of the spacer.

Genotoxicity of musk ketone

Thermal stabilities of perfluoropolyethers, Fomblin Z, Fomblin Y, Krytox, and Demnum in the presence of Al2O3 were examined. Fomblin Z was found to degrade at 200°C in two stages, the slow first stage, and the vigorous second stage leading to complete loss of fluid. It is concluded that oxide-to-halide conversion occurs on Al2O3 surface during the first stage. The second stage is attributed to a catalytic process induced by Lewis acid AlF3. Based on NMR and mass spectroscopic evidences the following reaction mechanism is advanced for the second stage: (1) a bidentate linkage is formed between an acidic aluminum and two oxygen atoms of an acetal unit (-O-CF2-O-) of Fomblin Z chains, and (2) the partial positive charge thus developed at the acetal carbon induces a fluorine atom transfer from the adjacent CF2 unit onto the acetal carbon and results in chain scission with transformation of the acetal sector into a methoxy end-group (-O-CF3) and the adjacent unit into either an acylfluoride end-group (FCO-CF2-), or a fluoroformate end-group (FCO-O-CF2-). Lacking acetal units Krytox and Demnum are stable against this degradation process. In the case of Fomblin Y, owing to the paucity of acetal units, no reaction was observed when heated in the presence of Al2O3; when heated with AlCl3, removal of acetal units and consequential formation of functional end-groups were observed.

Spectroscopic Analysis of Chain Conformation of Poly(propylene oxide)-Based Polymer Electrolytes

Fourier transform Raman spectroscopy has been utilized, in combination with normal coordinate analysis, to characterize chain conformational changes of amorphous poly(propylene oxide) (PPO) when used as a matrix for polymer electrolytes. Our data indicate that in the presence of salt, poly(propylene oxide) displays a characteristic Raman band at 810 cm -1 increasing in intensity with an increase in LiClO 4 concentration. 1,2-Dimethoxypropane (DMP) was found to be an excellent model for data interpretation. Both the intensity and frequency ofRaman active 1,2-dimethoxypropane vibrations were calculated. The C-C or C-O bands in the 700-900 cm -1 region were found to be particularly sensitive to chain conformational changes. The bands at 810 and 836 cm -1 were assigned to TG α T and TTT conformations of the -O-C-C-O- sequence along the backbone, respectively. Therefore an increase in intensity at 810 cm -1 directly correlates to an increase in the TG α T conformation with an increase in salt concentration. The effects of end groups on chain conformational changes were also studied since Li + can interact with both -OH end groups and ether oxygens. Poly(propylene oxide)s having hydroxy and methoxy end groups were compared. Our analyses indicate the interaction between hydroxy end groups and the lithium cation does not contribute as significantly to formation of the TG α T conformation as does the interaction between the ether oxygen and lithium cation.

Functionalization of Poly[(alkoxy)phosphazenes]: Synthesis and Characterization of Poly(phosphazenes) Containing Hydroxyl Groups

Methoxy end groups were cleaved from poly[bis(methoxyalkoxy)phosphazenes] {NP[(OCH 2 -CH 2 ) m OCH 3 ] 2 } n , where m = 2 (2, MEEP) and m = 1 (3, MEP) by reaction with trimethylsilyl iodide to give silylated polymers {NP[(OCH 2 CH 2 ) m OSiMe 3 ] x [(OCH 2 CH 2 ) m OCH 3 ] y } n (x + y = 2 ; m = 2 (4), m = 1 (5)). The silylated polymers 4 and 5 were hydrolyzed in a second step to yield the alcohol-functionalized polymers {NP[(OCH 2 CH 2 ) m OH] x [(OCH 2 CH 2 ) m OCH 3 ] y } n (m = 2 (6), m = 1 (7)). The structures of both classes of compounds were investigated by 31 P , 13 C , and 1 H NMR and infrared spectroscopies. The correlation between the amount of ISiMe 3 and the percentage of resultant alcohol functions was established. This latter was estimated by first using 1 H NMR and secondly 31 P NMR. In the latter case use was made of the reaction of a bicyclophosphane 8 with the OH groups in 6 and 7, which leads to bicyclophosphorane-functionalized polymers. The two results are in agreement. The presence of the alcohol function was confirmed by the observation of cross-linking through the reactions of 6 and 7 with a diisocyanate and a polyphosphazene functionalized by succinic anhydride groups. This functionalization reaction induces chain degradation of the polymer as the percentage of alcohol functions increases.

Thermodynamics of mixing of propylene oxide oligomers with different end groups and of statistical and block cooligomers of ethylene oxide and propylene oxide in tetrachloromethane

AbstractMixing enthalpies and Gibbs energies of liquid propylene oxide oligomers with hydroxyl and methoxy end groups and of block and statistical cooligomers of ethylene oxide and propylene oxide in tetrachloromethane are obtained by microcalorimetry and vapour pressure measurements. The thermodynamic excess quantities ΔH, ΔGE and ΔSE of mixing are influenced by induced dipol interactions of the ether segments with CCl4 and by the hydrogen bond interactions of the OH end groups. An expanded theoretical treatment using the Huggins approach of quasichemical equilibrium between the contacting segment surfaces is successfully applied on the experimental results.

Melting and Crystallization of Poly(oxyethylene) Mixtures

Solid-liquid eutectic phase diagrams of mixtures of poly(oxyethylene) (M.w. 2 000) with hydroxy and methoxy endgroups, crystallizing in extended-chain macroconformation only, with glutaric acid, benzoic acid or 1,2-diphenylethane are given. The composition dependence of the melting temperature can be fitted by the Flory-Huggins equation. Interaction parameters X and interaction energy densities B evaluated from the diluent branch of the phase diagram are consistent with those obtained from the polymer branch provided the calorimetric value of enthalpy of polymer fusion is used in the latter computation. Measurements of small- and wide-angle X-ray scatterings showed a stacked lamellar structure of POE. Below the eutectic melting point, the long period of the polymer is almost independent of the diluent concentration. On raising temperature gradually from this melting point to the melting point of pure polymer, the increasing long period indicates the penetration of the diluent between the lamellae. As follows from SAXS measurements, the crystallinity of poly(oxyethylene) in the mixtures remains unchanged compared to that of the pure polymer.

Polymer analysis using size-exclusion chromatography with coupled density and refractive index detection: VI. Molecular mass dependence of preferential solvation of polyoxyethylenes in chloroform with different ethanol contents

It is shown that preferential salvation of polyoxyethylenes with hydroxy and methoxy end-groups in chloroform containing ethanol takes place mainly at the hydroxy end-groups, but also along the main chain. A method is described that allows a separate determination of the adsorbed ethanol molecules per repeating unit and per end-group.