Mechanistic studies on ceric-amine initiated aqueous polymerization of methylmethacrylate by endgroup analysis

Summary Endgroup analysis of polymethylmethacrylate obtained by initiation with Ceric ion-amine initiator systems in acid aqueous media has been carried out using Palit's dye partition technique. The amines used are diethylamine, triethylamine, mono-ethanolamine, diethanol amine and triethanol amine and also ethylene diamine. All the amines incorporated amine endgroups in the polymer samples to the extent of approximately one endgroup per chain, except ethylene diamine which incorporated approximately two amine endgroups per macromolecule. Besides amine endgroups, the three ethanol amines incorporated hydroxyl endgroups to different extents depending on the hydroxyl content of the particular compound. In the light of endgroup results initiation through amine, ethylene diamine or ethanol amine radicals have been suggested. Probable termination mechanism has also been discussed.With 3 tables     

Synthesis of jasminaldehyde using magnesium organo silicate as a solid base catalyst

Synthetic talc (magnesium organo silicates; MOS) was synthesized by sol–gel method under non-hydrothermal conditions and modified by introducing amine/diamine functionalities in the interlayer space. The applicability of amine/diamine functionalized MOS was studied as catalysts for the synthesis of jasminaldehyde or -pentylcinnamaldehyde by condensation of 1-heptanal with benzaldehyde. The effect of amine/diamine functionality, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and temperature on the selectivity of jasminaldehyde was studied in detail. The highest conversion of 1-heptanal (99%) with 82% selectivity of jasminaldehyde was achieved using MOS3 as a catalyst. The rate constant for condensation of 1-heptanal with benzaldehyde was calculated under optimized reaction conditions. This is the first report on application of MOS as a solid base catalyst for the condensation of 1-heptanal with benzaldehyde.     

Stability of a model alkali-soluble associative polymer in the presence of a weak and a strong base

 Hydrophobically modified alkali-soluble emulsion (HASE) polymer is solubilized by the addition of a base. When the pH is increased to greater than 6.5, methacrylic acids on the polymer backbone are neutralized and the carboxylated latex polymer goes into solution causing a large increase in the viscosity due to inter-molecular associations of the hydrophobes. The stability of the viscosity of the polymer solution at pH in the range 9–10 was studied in the presence of a strong (NaOH) and a weak [1-amino-1-methylpropanol (AMP)] base. No change in the viscosity or the moduli was observed for the polymer in AMP. Reduction in the viscous and elastic properties of the polymer solution in NaOH was observed after 4 weeks. Such small changes are detectable using the superposition of oscillation on the steady shear technique. The decrease in the viscoelastic properties is attributed to the hydrolysis reaction of the urethane groups of the macromonomer, which resulted in a decrease in the number of hydrophobes per polymer chain. It is recommended that a weak base be used to neutralise the HASE polymer in order to avoid the possibility of compositional changes in the polymer after neutralisation for more than 6 weeks. Received: 19 May 1998 Accepted in revised form: 26 October 1998     

Production of organometallic polymers by the interfacial technique. V. Partial mechanistic study of the production of poly[alkyl(aryl)oxysilances]

A modified interfacial polymerization system capable of producing poly[alkyl(aryl)oxysilanes] consisting of a dichlorosilane in an organic solvent as octane and a diol in 2,5-hexanedione is presented. It is believed that polymerization occurs near the interface in the dione phase. The products are low to intermediate in molecular weight. As the nature of silane is varied, the rate of polymer formation varies, the silane with the most electron-deficient silicon giving the greatest rate. Molecular weight is constant as diol is changed but varies when the silane is changed so that the silane with the most bulky substitutes will give polymer with the lowest molecular weight. The results are consistant with a S_N2 type reaction mechanism.     

Development of Natural Rubber-Fibrous Nano Clay Attapulgite Composites: The Effect of Chemical Treatment of Filler on Mechanical and Dynamic Mechanical Properties of Composites

Common nano clay fillers have layered structure. Some nano clays like Attapulgite (AT), Sepiolite have rod like fibrous structure. Compared to layered structured clay fibrous clay AT can undergo better dispersion in polymer matrix leading to better improvement in composite properties. Chemical modifications of AT are done through amine treatment as well as by amine+silane treatment to get chemically modified fillers AAT and SAT respectively. In the present investigation, nano composites are prepared using natural rubber (NR) filled with AT, AAT and SAT. Three different loadings of each filler are used namely 2.5, 5, and 10 phr (parts per hundred of rubber). Mechanical properties like tensile strength, elongation at break increase with the increase in filler loading up to 5 phr there after these properties marginally fall when loading is increased to 10 phr due to problem of filler dispersion at higher loading. However, modulus at 300% elongation and tear strength increases with the increase in filler loading up to 10 phr. Very similar trend can also be observed for composites with chemically modified fillers, AAT and SAT. But the degree of reinforcement is higher in the case of AAT and SAT compared to that of unmodified filler AT for the same filler loading. This difference is mainly due to better polymer-filler interaction and filler dispersion in the case of chemically modified clays AAT and SAT compared to unmodified AT. Tear strength of composites increases remarkably with the addition of AT and which is further enhanced when chemically modified clays AAT and SAT are added. Dynamic-mechanical analyses of different clay composites give idea about the difference in the degree of polymer–filler interaction due to chemical treatment of filler.     

Production of organometallic polymers by the interfacial technique. I. Interfacial production of polyalkyloxysilanes and a study of some reaction variables

The first interfacial synthesis of polyalkyloxysilanes of the form where R′ = alkylene, and R″, R = alkyl or aryl is reported. It is found, in the range studied for the stirred systems, that as organic solvent viscosity and organic phase volume are increased, rate of polymer formation is decreased. Little difference in polymer formation rate is observed when the nature of the diol is varied, but considerable difference is noted when the nature of the organosilane is varied such that the most electropositive silane has the highest rate of polymer formation. Molecular weight is approximately constant as diol is changed but varies markedly when the silane is changed, so that the silane with the most bulky substance will give polymer with the lowest molecular weight.     

Effect of amine catalysts on preparation of nanometric SiO<Subscript>2</Subscript> particles and antireflective films via sol–gel method

SiO₂ sols were prepared by hydrolysis and condensation reactions of tetraethyl orthosilicate through a one step acid or a two step acid + base catalysis process, in the presence of nitric acid and four different base catalyzers, namely trimethylamine, triethylamine, tripropylamine and tributylamine. Hydrolysis of TEOS was followed by FT-IR analyses. Particle size distributions of the sols were evaluated after predetermined durations in 1–22 days. Particle growth was seen to be faster in amine catalyzed systems than in one step acid catalyzed system. The highest rate of growth was in triethylamine catalyzed system. Glass substrates were dip coated with the prepared SiO₂ sols. Effect of sol aging duration on film thickness and on light transmittance properties of the films was investigated with respect to type of base catalyst. Thicknesses of the films which were measured to be in the range of 100–400 nm, were seen to increase with aging duration of the sols. Triethylamine catalyzed system presented the highest film thickness. Films obtained from one step acid catalyzed system presented an increase of 4.8%; whereas acid + base catalyzed films provided an increase in the light transmittance of 5.7% in the first 4 days of aging. Surfaces of films were examined by FESEM and AFM. The antireflective character of the films was verified by diffuse reflectance analyses.     

Chalcone and cinnamate synthesis via one-pot enol silane formation-Mukaiyama aldol reactions of ketones and acetate esters

Aryl alkyl ketones, acetate esters, and acetamides undergo facile one-pot enol silane formation, Mukaiyama aldol addition, and dehydrosilyloxylation in the presence of an amine base and excess trimethylsilyl trifluoromethanesulfonate. The chalcone and cinnamate products are generally recovered in high yield. The relative stoichiometry of the trimethylsilyl trifluoromethanesulfonate and amine base reagents determines whether the reaction yields the β-silyloxy carbonyl product or the α,β-unsaturated carbonyl.     

Chemistry of the phenoxathiins and isosterically related heterocycles. XXV . Synthesis of 1,6-diazathianthrene from 3-mercaptopyridin-2(1H)-thione via a novel dehydrothiolation reaction in the presence of triethylamine

The generation of the dianion of 3-mercaptopyridin-2(1H)-thione with triethylamine in N,N-dimethylform-amide followed by reaction in the presence of 2-chloronitrobenzene fails to give 1-azathianthrene which is formed in good yield when sodium hydride was employed as the base. The principle product isolated from the reaction was instead 1,6-diazathianthrene. Mechanistic considerations are discussed.     

Interpreting the signal from a localized fluorescence sensor: a study by angle-resolved XPS and dynamic SIMS

Angle-resolved X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectroscopy (DSIMS) experiments were conducted to assess the interactions between a diamine curing agent and a glycidoxysilane-modified glass substrate. This effort was motivated by earlier work, in which a fluorescent probe localized in dilute quantities in the silane layer was used to track the penetration of the resin into the silane layer, as well as the resin cure. XPS and DSIMS experiments were performed on the silane layers immersed only in the resin hardener, providing more detailed information about the concentration profile and structural reorganization within the silane layer due specifically to hardener penetration. Dynamic SIMS spectra reveal the presence of hardener in the layer, as indicated by the strong CN- signal throughout the silane layer thickness. The XPS results indicate the presence of an amine gradient within the top 10 nm of the silane coating, with less amine penetration deeper into the silane layer. The XPS data also suggest some level of anisotropy in the molecular structure of the diamine/glycidoxysilane coating, as revealed by the differences in the relative atomic concentrations and peak positions of the C1s components at two different take-off angles.     

Kinetics and thermodynamics of amine and diamine signaling by a trifluoroacetyl azobenzene reporter group

[reaction: see text] (Trifluoroacetyl)azobenzene dyes were previously employed as amine reporter groups (chemosensors) in a dendrimer-based monomolecular imprinting system. Kinetic and binding studies with a range of amines and diamines show that the highly selective signaling observed for alkane diamines by these imprinted dendrimers arises from a kinetic effect due to intramolecular general base-catalyzed carbinolamine formation with the dye itself. The relationship between diamine structure and carbinolamine stability and rate of formation is described.     

Versatile bio-ink for covalent immobilization of chimeric avidin on sol-gel substrates

A bio-ink for covalent deposition of thermostable, high affinity biotin-binding chimeric avidin onto sol-gel substrates was developed. The bio-ink was prepared from heterobifunctional crosslinker 6-maleimidohexanoic acid N-hydroxysuccinimide which was first reacted either with 3-aminopropyltriethoxysilane or 3-aminopropyldimethylethoxysilane to form silane linkers 6-maleimide-N-(3-(triethoxysilyl)propyl)hexanamide or -(ethoxydimethylsilyl)propyl)-hexanamide. C-terminal cysteine genetically engineered to chimeric avidin was reacted with the maleimide group of silane linker in methanol/PBS solution to form a suspension, which was printed on sol-gel modified PMMA film. Different concentrations of chimeric avidin and ratios between silane linkers were tested to find the best properties for the bio-ink to enable gravure or inkjet printing. Bio-ink prepared from 3-aminopropyltriethoxysilane was found to provide the highest amount of active immobilized chimeric avidin. The developed bio-ink was shown to be valuable for automated fabrication of avidin-functionalized polymer films.     

Polymerization photoinitiated by carbonyl compounds. X. Methyl methacrylate polymerization photoinitiated by fluorenone in the presence of triethylamine

The photoinitiation efficiency of the fluorenone/triethylamine (TEA) system in the polymerization of methylmethacrylate (MMA) has been evaluated as a function of the monomer concentration, the amine concentration, and the polarity of the reaction medium. The polymerization proceeds readily in low polarity media (benzene/monomer), but it is negligible in more polar solvents (acetonitrile/monomer). The polymerization rate increases with the amine concentration up to 0.01 M TEA. Further increase in amine concentration produces a decrease in the polymerization rate. A similar behavior was observed for the fluorenone photoreduction yield and the yield of fluorenone derived radicals. All these processes are considered to involve the excited triplet, while quenching of the excited singlet by the amine decreases the rate of these processes. However, the decrease in photoinitiation efficiency observed at high amine concentration is larger than that expected from the singlet quenching extent, as estimated from the effect of the amine on the fluorescence yield under the same experimental conditions. This discrepancy indicates that other process(es) must contribute to the protection afforded by high amine concentrations. Quenching of the charge transfer intermediate by the amine is postulated as a competitive process that could explain the above mentioned effects. © 1994 John Wiley & Sons, Inc.     

Synthesis of organofunctional silanes with sterically hindered substituents at silicon atoms

Organofunctional silanes with more sterically hindered substituents at the silicon atom than the typical methoxy (ethoxy) group have lately been frequently used as silane coupling agents, in polymer coupling systems, sol‐gel processes and also as interpenetrating polymer network substrates. New and very efficient synthetic ways leading to organofunctional silanes of the above type with methacryl, amine, chloro and isocyanato functional groups are proposed here. Catalytic transesterification and/or alcoholysis of chloropropyltrialkoxysilanes followed by­nucleophilic substitution has been employed. Copyright © 2001 John Wiley & Sons, Ltd.     

A tandem enol silane formation-Mukaiyama aldol reaction mediated by TMSOTf

A slight excess of silyl trifluoromethanesulfonate mediates a tandem enol silane formation-Mukaiyama aldol reaction in the presence of Hunig’s base. Preformation of the enol silane is unnecessary for efficient reactions, which proceed in 75-97% yield for the addition of aryl methyl ketones and acetate esters to non-enolizable aldehydes. Mechanistic data suggests that free amine is crucial for full conversion.     

Reaction of (3-Aminopropyl)dimethylethoxysilane with Amine Catalysts on Silica Surfaces

The gas-phase reaction of (3-aminopropyl)dimethylethoxysilane (APDMES) with silica with and without amine catalysts has been studied using infrared spectroscopy. Evidence is provided that shows that the aminosilane initially adsorbs via hydrogen bonding of both ethoxy and aminopropyl moieties of the silane with the surface hydroxyl groups. As the reaction proceeds, the number of silane molecules attached to the surface via a Si-O-Si linkage increases primarily at the expense of the number of H-bonded ethoxy groups. The conversion is due to a catalytic process involving the aminopropyl end of gaseous APDMES molecules. On the other hand, the H-bonded aminopropyl groups are less reactive and only a small portion of these groups participates in Si-O-Si bond formation. At the end of the reaction there remain about 50% of the adsorbed APDMES attached by the H-bonded aminopropyl group. Attempts to block the adsorption of the aminopropyl end through the use of the more strongly H-bonded triethylamine proved unsuccessful. The use of preadsorbed triethylamine or 1 : 10 mixtures of triethylamine/APDMES accelerates the reaction but in the end leads to the same final distribution of products on the surface. Copyright 2000 Academic Press.     

Benzophenone/triethylamine-photoinitiated polymerization of methyl acrylate

Benzophenone-sensitized photopolymerization of methyl acrylate was shown to be remarkably enhanced by the addition of small amounts of triethylamine. This was attributed to the efficient formation of an electron-transfer complex between photoactivated benzophenone and ground-state amine. Ketyl and amine free radicals derived from this complex were postulated to be the chain-initiating species. Quantum yield experiments indicated that methyl acrylate itself was also a quencher of the benzophenone triplet state.     

Modification of ion-exchange membrane used for separation of protons and metallic cations and characterization of the membrane by current-voltage curves

The ionic transport properties of several cations (H(+), Na(+), and Zn(2+)) across sulfonated ion-exchange membranes modified with an amine were investigated by the measurement of current-voltage curves to determine the effect of the surface modification of the membrane. The membrane was modified by chlorosulfonation and amination with a diamine (N,N-dimethylethylenediamine) and an amine (isoamylamine) to form a sulfonamide bond between amine groups and the surface layer. In the case of the modification with the diamine, the terminal amine was protonated in acidic media or quaternized with methyl iodide. The presence of a positively charged layer on the two sides of the membrane strongly decreased the limiting current flowing across the membrane in the presence of a 1:1 electrolyte such as HCl or HNO(3) due to an increase of the resistance of the membrane. In the case of divalent cations such as Na(+) and Zn(2+), electrostatic repulsion also contributes to the decrease of the limiting current. The presence of divalent anions seems to increase the limiting current somewhat due to their preconcentration within the cationic layer, which facilitates their subsequent transport across the membrane. When only one face of the membrane was modified, the current-voltage measurements showed that the membrane did not behave like a bipolar membrane. For one-side (under forward polarization) and two-side modified membranes, counterions are slightly blocked in the membrane by the cationic layer, which led to a decrease of the membrane conductivity during electrodialysis.     

含氧光敏引发体系的研究——Ⅵ.二苯酮/三乙胺体系引发光聚合过程中的再次引发效应

A sequential photoinitiation. phenomenon was found in the benzophenone/triethylamine/ MMA radical photopolymerization system, which leads to increase of molecular weight, amine content of polymer formed with progressive irradiation time. The results, obtained demonstrate that the sequential photoinitiation originates from the photoreaction of active amine groups at the polymer chains with excited benzophenones producing a polymer radicals, which induce sequential polymerization. The effects of benzophenone and amine concentrations,oxygen co-ntent and chain requlator were studied. Reaction mechanism was also discussed.     

含氧光敏引发体系的研究——Ⅵ.二苯酮/三乙胺体系引发光聚合过程中的再次引发效应

过去,作者曾发表了多种光敏引发体系引发烯类单体光聚合的工作,在研究2,2-二甲氧基苯乙酮在氧存在下引发甲基丙烯酸甲酯光聚合时,结合在聚合物链端的引发剂碎片具有光化学活性,在光聚合反应中产生高分子自由基,发生再次聚合,出现高分子量