Atom transfer radical polymerization of (meth)acrylates and their novel block copolymers with vinyl acetate

Homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) were carried out at 90 °C using methyl-2-bromopropionate (MBP) as initiator, copper halide (CuX, X=Cl, Br) as catalyst, 2,2^′-bipyridine (bpy) or N,N,N^′,N^′,N^″-pentamethyldiethylenetriamine (PMDETA) as ligand in 1-butanol (less polar and containing OH) and acetonitrile (more polar) solvents. It was found that with CuCl/bpy catalyst ATRP of MA and MMA in 1-butanol proceeded faster than that in acetonitrile. The rate of ATRP of MA and MMA in acetonitrile and 1-butanol was comparable when CuCl/PMDETA used as catalyst system. The number-average molecular weights increased with conversion and polydispersities were low . The ATRP of MA and MMA with vinyl acetate telomer having trichloromethyl end group (PVAc-CCl₃) were also used to synthesize new block copolymers. The structures and molecular weight of synthesized PVAc-b-PMA and PVAc-b-PMMA were characterized by ¹H NMR, FTIR spectroscopy and gel permeation chromatography (GPC) and shown that the block copolymers were novel.     

Synthesis and characterization of amphiphilic star copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate: Effects of architecture and composition

Six amphiphilic star copolymers comprising hydrophilic units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic units of methyl methacrylate (MMA) were prepared by the sequential group transfer polymerization (GTP) of the two comonomers and ethylene glycol dimethacrylate (EGDMA) cross-linker. Four star-block copolymers of different compositions, one miktoarm star, and one statistical copolymer star were synthesized. The molecular weights (MWs) and MW distributions of all the star copolymers and their linear homopolymer and copolymer precursors were characterized by gel permeation chromatography (GPC), while the compositions of the stars were determined by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Tetrahydrofuran (THF) solutions of all the star copolymers were characterized by static light scattering to determine the absolute weight-average MW () and the number of arms of the stars. The of the stars ranged between 359,000 and 565,000 g mol⁻¹, while their number of arms ranged between 39 and 120. The star copolymers were soluble in acidic water at pH 4 giving transparent or slightly opaque solutions, with the exception of the very hydrophobic DMAEMA₁₀-b-MMA₃₀-star, which gave a very opaque solution. Only the random copolymer star was completely dispersed in neutral water, giving a very opaque solution. The effective pKs of the copolymer stars were determined by hydrogen ion titration and were found to be in the range 6.5-7.6. The pHs of precipitation of the star copolymer solutions/dispersions were found to be between 8.8-10.1, except for the most hydrophobic DMAEMA_10-b-MMA₃₀-star, which gave a very opaque solution over the whole pH range.     

Cationic Heteroconjugation Constants in the OHN+ and NHO+ Systems in Propylene Carbonate: Dependence on Difference in Basicity

Cationic heteroconjugation equilibria of more than ninety systems consisting of substituted pyridines, their N-oxides, and trimethylamine N-oxide, i. e., in systems with mixed hydrogen bridges of type OHN⁺ (NHO⁺) were studied in propylene carbonate. Both experimental systems without proton transfer, BH⁺/B₁, and those with proton transfer, B₁H⁺/B, were explored. The stability of the mixed hydrogen bridges, OHN⁺ (NHO⁺), is compared with that of the OHC⁺-type bridges. The influence of the difference in basicity of the conjugate base of the proton donor and the proton acceptor on the presence of the proton transfer equilibria, and, consequently, the possibility of determination of the cationic heteroconjugation constant values is discussed.     

Formation of π-Allyl Palladium Complexes from Tertiary Alcohols

Reactions of 2-methyl-2-propanol, 2-methyl-2-butanol, 2-methyl-2-pentanol, 1-methyl-1-cyclohexanol, and 1-ethyl-1-cyclohexanol with palladium(II) tetraaqua complex in a perchloric acid medium give carbonyl and aromatic compounds, as well as the corresponding palladium -allyl complexes. The complexes were isolated from the reaction mixtures by way of formation of 2,2'-bipyridine complexes and characterized by the elemental analyses and ¹H and ¹³C NMR spectra. The main direction of transformation of acyclic alcohols is formation of complexes with no alkyl substituents at the central carbon atom of the allyl ligand; with cyclic alcohols, exocyclic complexes are formed.     

Glass transition temperature modification of acrylic and dienic type copolymers of 4-chloromethyl styrene with incorporation of (Me3Si)3C- groups

The new functional styrenic monomer, 4-trisylmethyl styrene (TsiMS) [Tsi=trisyl=tris(trimethylsilyl)methyl], was synthesized by reacting 4-chloromethyl styrene (CMS) with trisyllithium (TsiLi) in tetrahydrofuran (THF) solvent in the presence of copper chloride (CuCl). Attempt for the free radical polymerization of TsiMS by α,α^′-azobis(isobutyronitrile) (AIBN) as an initiator at 70 ± 1 °C failed for several periods of times. This result showed that the trisyl group is a highly sterically hindered substituent and, subsequently, TsiMS becomes resistant for polymerization. Therefore, for preparation of new methacrylic, acrylic and dienic copolymers of TsiMS, we firstly synthesized the copolymers of CMS with different monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (BA) and isoprene (IP) by free radical polymerization method in toluene solution at 70 ± 1 °C using AIBN initiator to give the copolymers I-VI in good yields. The copolymer compositions were obtained using related ¹H NMR spectra and the polydispersity indices of the copolymers determined using gel permeation chromatography (GPC). The trisyl groups were then covalently attached to the obtained copolymers as side chains by reaction between excess of TsiLi and benzyl chloride bonds of CMS units, to give the copolymers - in 80-92% yields. All the resulted polymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility of all the copolymers was examined in various polar and non-polar solvents. The glass transition temperature (T_g) of all copolymers was determined by differential scanning calorimetry (DSC) apparatus. The T_g value of copolymers containing bulky trisyl groups was found to increase with incorporation of trisyl groups in polymer structures. The presence of trisyl groups in polymer side chains, create new macromolecules with novel modified properties.     

Ternary complexes of N-(2-acetamido)iminodiacetic acid and some aromatic acids. Isolation and stability constants in solution

Summary Ternary 1:1:1 complexes of Y^III, Co^II, Ni^II, Cu^II, La^III, Ce^III and UO ₂ ²⁺ with N-(2-acetamido)iminodiacetic acid (H₂ADA) as primary ligand and salicylic, anthranilic or phthalic acid as secondary ligand are described. The complexes of Co^II and Cu^II were isolated and characterized by microanalysis, molar conductance measurements, thermal analysis, i.r. and u.v.-vis. spectra. The formation constants of the 111 ternary complexes were determined potentiometrically in 20% (w/w) EtOH-H₂O at 24 °C. The stabilities of the 111 M ⁿ⁺ :ADA^2–:aromatic acid ternary complexes are higher than those of the corresponding 11 M ⁿ⁺ :aromatic acid binary complexes.     

Advanced CPMAS-13C NMR techniques for molecular characterization of size-separated fractions from a soil humic acid

A humic acid extracted from a volcanic soil was subjected to preparative high-performance size-exclusion chromatography (HPSEC) to reduce its molecular complexity and eleven different size fractions were obtained. Cross-polarization magic-angle spinning ¹³C NMR (CPMAS ¹³C NMR) analysis performed with variable contact-time (VCT) pulse sequences showed that the largest molecular-size fractions contained aromatic, alkyl, and carbohydrate-like components. The carbohydrate-like content and the alkyl chain length seemed to decrease with decreasing molecular size. Progressive reduction of aromatic carbon atoms was also observed with decreasing molecular size of the separated fractions. Mathematical treatment of the results from VCT experiments enabled cross polarization (T _CH) and proton spin–lattice relaxation () times to be related to structural differences among the size fractions. The conformational distribution indicated that the eleven size fractions could be allocated to two main groups. The first group, with larger nominal molecular sizes, was characterized by molecular domains with slower local molecular motion. The second group of size fractions, with smaller nominal molecular sizes, was characterized by a larger number of molecular domains with faster local molecular motion. The T _CH and values suggested that either condensed or strongly associated aromatic systems were predominant in the size fractions with the largest apparent molecular dimensions.     

On a possible excited state proton transfer in N-formylkynurenine derivatives

It is shown that intramolecular hydrogen bonding between the

and the ortho carbonyl on the side chain of N'formylkynurenine and some parent compounds plays an important role on their spectroscopic properties. The fluorescence emissionλ_max is shifted by about 4000 cm^?1 in going from polar to non-polar solvents. This abnormally red-shifted fluorescence is attributed to an excited state proton transfer from the formamido to the ortho carbonyl of the side chain.     

1H NMR Analysis of Heteroassociation of Caffeine with Mitoxanthrone in Aqueous Solution

Heteroassociation of caffeine (CAF) with the antibiotic mitoxanthrone (novatrone, NOV) in aqueous solution was studied by one-dimensional (1D) and two-dimensional (2D) ¹H NMR spectroscopy (500 MHz). The concentration and temperature dependences of the proton chemical shifts of the molecules in aqueous solution have been measured. The equilibrium constants of heteroassociation between CAF and NOV and the limiting proton chemical shifts of the aromatic ligands of the associates have been determined. The most plausible structure of the 1:1 CAF–NOV heterocomplex in aqueous solution was inferred from the calculated values of the induced proton chemical shifts and quantum-mechanical screening curves for CAF and NOV. The thermodynamic parameters of the formation of the CAF–NOV heterocomplex have been calculated. The relatively high heteroassociation constant (K = 256 ± 31 M^–1, T = 318 K), the positive value of entropy for heteroassociation [ S = 15.3 ± 4.0 J/(moleK)], and the structural features of the chromophore of the novatrone molecule indicate that hydrophobic interactions play a significant role in stabilization of the CAF–NOV heterocomplex.     

Molecular miscible blend of poly(2-cyano-1,4-phenyleneterephthalamide) and polyvinylpyrrolidone characterized by two-dimensional correlation FTIR and solid state C NMR spectroscopy

Miscibility of blends of poly(2-cyano-1,4-phenyleneterephthalamide/polyvinylpyrrolidone) (CN-PPTA/PVP) was investigated by dilute solution viscometry, two-dimensional (2D) correlation Fourier transformed infrared (FTIR) spectroscopy and solid state ¹³C NMR spectroscopy. It was shown that a large proportion of the PVP, the water-soluble component, could not be removed from CN-PPTA by extraction with water, and even with boiling water for blend films, suggesting that the flexible aliphatic PVP chain forms a blend with the rigid aromatic CN-PPTA chain through strong intermolecular interaction making it too difficult to dissolve even in boiling water. Viscometry on a polymer mixture of dilute solution showed that [η]_exp exhibited larger value than [η]_theo in all mixtures used in this experiment, suggesting occurrence of a strong attractive interaction between the two polymers. 2D correlation FTIR spectroscopy revealed that the carbonyl absorption band of PVP at 1675 cm⁻¹ shifted to a new low frequency absorption band at 1640 cm⁻¹ with a change of 35 cm⁻¹, suggesting strong hydrogen bonding with NH (amide II) proton of CN-PPTA. Another new absorption band at 1685 cm⁻¹ was due to the carbonyl absorption band of CN-PPTA shifting to a higher frequency than that at 1662 cm⁻¹, indicating that some of the carbonyl groups in the CN-PPTA components of the blends were in a free state or in a non-hydrogen bonded state as a consequence of the participation of NH proton of CN-PPTA in hydrogen bonding, resulting in the absorption bands of NH bend deformation of CN-PPTA at 1542 and 1313 cm⁻¹ being shifted to higher wavenumber of 1556 and 1324 cm⁻¹, respectively. Solid state ¹³C NMR spectroscopy revealed a chemical shift for CO of the PVP component in the blend fiber changing down-field (shift to left) at 177.346 ppm with a difference of 1.812 ppm; this was due to a lower electron density around the carbon atom of CO of lactam via hydrogen bonding with NH proton of amide in the CN-PPTA component, suggesting that a homogeneous blend of the CN-PPTA and PVP was produced on a molecular scale via hydrogen bonding.     

Acetylene–norbornene copolymers

Metathesis ring opening polymerization has been used to copolymerize norbornene and 7,8-bis(trifluoromethyl)tricyclo[4,2,2,0^2,5]deca-3,7,9-triene. Subsequent thermal elimination of the precursor copolymers yielded acetylene–norbornene copolymers. The undoped copolymers were found to have electrical conductivity, spin concentration, and EPR linewidths which vary with composition. The location of the trans-C? H out-of-plane vibration, however, was invariant at 1010cm^?1 indicating that conjugation length of n > 4 are present even at 40% acetylene content in the copolymer. The copolymers containing 79 mol % of acetylene units attained a doped conductivity of 0.02 S/cm with a dopant concentration of 6 mol % of I per sp² carbon.     

Polyacrylonitrile Block Copolymers for the Preparation of a Thin Carbon Coating Around TiO2 Nanorods for Advanced Lithium‐Ion Batteries

Herein, a new method for the realization of a thin and homogenous carbonaceous particle coating, made by carbonizing RAFT polymerization derived block copolymers anchored on anatase TiO₂ nanorods, is presented. These block copolymers consist of a short anchor block (based on dopamine) and a long, easily graphitizable block of polyacrylonitrile. The grafting of such block copolymers to TiO₂ nanorods creates a polymer shell, which can be visualized by atomic force microscopy (AFM). Thermal treatment at 700 °C converts the polyacrylonitrile block to partially graphitic structures (as determined by Raman spectroscopy), establishing a thin carbon coating (as determined by transmission electron microscopy, TEM, analysis). The carbon‐coated TiO₂ nanorods show improved electrochemical performance in terms of achievable specific capacity and, particularly, long‐term cycling stability by reducing the average capacity fading per cycle from 0.252 mAh g^–1 to only 0.075 mAh g^–1.

     

Structural and thermodynamic analysis of heteroassociation of daunomycin and flavin mononucleotide molecules in water by <Superscript>1</Superscript>H NMR spectroscopy

Heteroassociation of the antitumor antibiotic daunomycin (DAU) with flavin mononucleotide (FMN) has been investigated by one-and two-dimensional ¹H NMR spectroscopy (500 MHz) in a water solution to determine the molecular mechanism of the combined action of the antibiotic and vitamin in the FMN-DAU system. The equilibrium constants of the reactions, induced proton chemical shifts, and thermodynamic parameters (ΔH, ΔS) of heteroassociation were determined from the concentration and temperature dependences of the proton chemical shifts in the interacting aromatic molecules. Analysis of the results indicate that heterocomplexes of riboflavin mononucleotide and daunomycin are formed due to stacking interactions between aromatic chromophores. The most probable spatial structure of the 1:1 DAU-FMN heterocomplex was determined by the molecular dynamics method using the X-PLOR program and the results of the analysis of the induced proton chemical shifts in molecules. Calculation of the relative content of self-and hetero-complexes of daunomycin for different values of the ratio (r) between the concentrations of flavin mononucleotide and daunomycin demonstrated that for r > 3, the contribution of DAU-FMN heterocomplexes to the equilibrium distribution of associates in aqueous solution is dominant. It is concluded that the aromatic molecules of vitamins, in particular, riboflavin, can form energetically strong heteroassociates with antitumor antibiotics in water solution and can thereby affect their medical and biological activity.     

Gas-phase CαCβ double bond cleavage in the dissociation of protonated 2-benzylidenecyclopentanones: Dissociative proton transfer and intramolecular proton-transport catalysis

Among gas-phase dissociation reactions, double bond cleavage reaction appears to happen extremely rare, especially in the case of CC double bond. In the dissociation reaction of protonated 2-benzylidenecyclopentanones in tandem mass spectrometry, the formation of benzyl cations was observed, resulting from the cleavage of C^α=C^β double bonds, which is different from the general cleavage route seen in most α, β-unsaturated ketone cases. A combined experimental and theoretical investigation on intramolecular hydrogen transfers was carried out to illustrate the mechanisms. The external proton is initially localized on the carbonyl oxygen (the thermodynamically-preferred protonation site). Upon collisional activation, the mobile proton stepwise migrates to the C^α position to achieve the reduction and subsequent cleavage of the C^α=C^β double bond. The stepwise proton transfer is achieved via intramolecular proton-transport catalysis with the assistance of the phenyl ring. The ortho position of the phenyl accepts the proton from the carbonyl oxygen via a 1,6-H shift, and then donates it to the C^α stepwise. The conventional 1,3-H shift from the carbonyl oxygen to the C^α position can be excluded in this case due to its significant energy barrier. Further isotope-labeling experiments are applied to confirming the reaction mechanism. Last but not least, the scope-expansion experiments indicates that the aromatic and cycloalkanonyl moieties play a crucial roles in the cleavage reaction of C^α=C^β double bond.     

FIA Amperometric Determination of Molybdenum(VI) Based on the Catalysis of the Hydrogen Peroxide-Iodide Reaction

An analytical approach to FIA amperometric determination of molybdenum based on the well-known catalytic reaction involving the oxidation of iodide by hydrogen peroxide is proposed. The indirect method involves measurements of triiodide at a glassy carbon electrode polarised at +0.2V in a flow-through configuration. The limit of detection was found to be 6×10^–9molL^–1, and the dynamic concentration range was established as 1×10^–7molL^–1 to 5×10^–5molL^–1. The repeatability of measurements was determined as 2.1% (n = 20). The amount of Mo in a steel sample was determined after removing the additive interference from iron by using fluoride ions, and the results were in good agreement with the certified value. Interference of other metallic ions is addressed.     

NMR Study of the Stoichiometry, Stability, and Ligand Interchange of Silver Ion-Hexathia-18-crown-6 Complex in Binary Dimethyl Sulfoxide Solvent Mixtures at 300 K

Proton NMR was used to study the complexation reaction between silver ion and hexathia-18-crown-6 in a number of binary mixed solvents of dimethyl sulfoxide with acetonitrile and methanol. Formation constants for the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. The influence of solvent composition on the stability of the resulting complex is discussed. The exchange kinetics of Ag⁺-hexathia-18-crown-6 in 70-30 wt.% dimethyl sulfoxide-acetonitrile and 75-25 wt.% dimethyl sulfoxide-methanol were studied by proton NMR line-shape analysis. In both solvent mixtures, the exchange of thiacrown ether between the free and complexed sites was found to proceed via a dissociative pathway. The exchange rates and the activation parameters E _a, H , S, and G for the ligand exchange were determined and the influence of solvent properties on these parameters discussed.     

The effects of overall composition and monomer sequence distribution on the infrared carbonyl stretching frequencies of ethylene–vinylacetate and styrene–vinylacetate copolymers

The vinyl acetate centered triad fractions of some free radically prepared ethylene–vinyl acetate and styrene–vinyl acetate copolymers have been determined from the patterns of vinyl acetate methine carbon peaks in their ¹³C nuclear magnetic resonance (NMR) spectra. The positions and shapes of the carbonyl bands in the infrared (IR) absorption spectra of the copolymers recorded in chloroform are shown to depend on the compositions of the copolymers and on the proportions of the various vinyl acetate centered triads. Infrared absorption measurements may thus be used in part to characterize the monomer sequence distributions of these copolymers.     

Zur Berechnung und Auswertung der bei der Pyrolyse/Gaschromatographie entstehenden Fragmentverteilungen von Copolymeren mit langen Äthylensequenzen

Zusammenfassung Eine theoretische Grundlage wurde aufgestellt zur Auswertung der Daten aus der Pyrolyse mit Hydrierung und Gaschromatographie von Copolymeren mit langen Äthylensequenzen. Die untersuchten Äthylen-Propylen Copolymeren waren entweder inaktiv oder an der -CH₃-Gruppe mit Tritium markiert. Die in den vorangegangenen Arbeiten an den Homopolymeren untersuchten thermischen Spaltungsmechanismen konnten auf die Copolymeren übertragen werden. Hier unterscheidet man die Spaltungen der Bindungen am tertiären C-Atom von den sogenannten_s-Spaltungen innerhalb der Äthylensequenzen. Eine C-C-Bindung in einer - oder ß-Position zu einem tertiären Kohlenstoff spaltet etwa doppelt so häufig wie eine solche in einem -CH₂-Kettensegment. Im allgemeinen erfolgt eine Überlagerung von statistischem und nichtstatistischem Abbau. Unter der Annahme von primärer statistischer Spaltung wurden die Verteilungen der Normalalkane und Methylalkane sowie deren Aktivität berechnet. Die experimentellen Verteilungen für die Fragmente ab C₁₁ ergeben denselben Abfall mit der Fragmentlänge wie aus der statistischen Theorie berechnet. Auch unter verschiedenen experimentellen Bedingungen ergeben sich so dieselben Sequenzlängenverteilungen des Äthylens. Diese Theorie wurde auch an Fragmentverteilungen von Copolymeren aus Äthylen mit Propylen und einer Terkomponenten sowie aus Äthylen mit -Olefinen (z. B. mit 1-Buten) nachgeprüft. Berücksichtigt man einen speziellen Abbaumechanismus, so kann nach dieser Methode auch die Sequenzlängenverteilung in Äthylen-Vinylacetat-Copolymeren aus Pyrogrammen ermittelt werden.

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Summary A theoretical basis has been established for evaluating the data obtained from pyrolysis with hydrogenation and gas chromatography of copolymers with long ethylene sequences. The ethylene-propylene copolymers investigated were either inactive or were labelled at the a-CH3-group in the propylene units with tritium. The mechanism of thermal decomposition studied previously at the homopolymers could be extended to the copolymers. Here, cleavages of C-C-bonds at tertiary carbon atoms are distinguished from the so-calleds-scissions within ethylene sequences. A C-C-bond in an – or ß-position to a tertiary carbon cleaves about two times more readily than a C-C-bond in a linear —CH₂-chain segment. Generally there is an overlapping of random cleavages with nonstatistical decomposition. Assuming primarily random scissions, the distributions of the normal alkanes and of the methylalkanes as well as their activity has been calculated. The experimental distributions for the fragments C₁₁ and longer exhibit the same slope as calculated from the statistical theory. By variation of experimental conditions the same sequence distribution of ethylene was obtained. This theory was checked also with fragment distributions from copolymers of ethylene with propylene and a ternary component as well as of ethylene with -olefines (e.g. 1-butene). By considering a particular decomposition, the sequence distribution in ethylene-vinyl-acetate copolymers can also be evaluated from pyrograms with this method.

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Herrn Professor Dr.G. Rehage zum 60. Geburtstag gewidmet.

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Mit 4 Abbildungen und 1 Tabelle