bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics, mechanisms, and synthesis studies of difunctional aminopropyl terminated polydimethylsiloxane oligomers
Authors: McGrath J. E. , Sormani P. M. , Elsbernd C. S. , Kilic S. 
Published: March 2011

AbstractThe anionic ring opening equilibration polymerization of octamethylcyclotetrasiloxane (D4) initiated with siloxanolates in the presence of 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane (DSX) was investigated. The disiloxane serves as an effective chain transfer agent and source of aminopropyl functionality. Techniques for following the polymerization utilizing gas chromatography and high pressure liquid chromatography (HPLC) were developed and verified to be comparable with alternate methods published in the literature. In these polymerizations, it was concluded that the quaternary siloxanolate led to much more rapid polymerizations than the corresponding potassium based initiators. In all cases, the cyclic tetramer disappeared more rapidly than the disiloxane. However, this does not limit the utilization of the DSX for the synthesis of controlled molecular weight, difunctional species. Polar impurities, such as water in the disiloxane, were shown to influence the reactivity in these systems, especially at relatively low initiator concentrations. The work is continuing and many issues are being addressed, currently in a more quantitative fashion using the analytical procedures developed in the current study.
Free radical ring‐opening polymerization and its use to make biodegradable polymers and functionally terminated oligomers
Authors: Bailey William J. , Chen Paul Y. , Chen Shuh‐Cheng , Chiao Wen‐Bin , Endo Takeshi , Gapud Benjamin , Kuruganti Vijaya , Lin Yin‐Nian , Ni Zhende , Pan Cai‐Yuan , Shaffer Scott E. , Sidney Luann , Wu Shang‐Ren , Yamamoto Noboru , Yamazaki Noboro , Yonezawa Kazuya , Zhou Lin‐Lin 
Published: March 2011

AbstractSince a carbon‐oxygen double bond is considerably more stable than a carbon‐carbon double bond, it has been possible to use this driving force to promote free radical ring‐opening polymerization of unsaturated heterocyclic compounds. This process, for the first time, has permitted the introduction of functional groups, such as esters, amides and carbonates, into the backbone of addition polymers. Hydrolysis of the copolymers with common monomers produced oligomers capped with hydroxyl, amino or carboxylic acid groups. The presence of an ester group in a copolymer, such as in a copolymer of ethylene, render the copolymer biodegradable.
NMR spectroscopic investigation on polymerization mechanisms of amino acid NCAS
Authors: Kricheldorf Hans R. 
Published: March 2011

AbstractPolymerizations of α‐aminoacid N‐carboxyanhydrides (α‐NCAs) can be initiated by nucleophilic or basic reagents. Depending on the nature of the reagent, nucleophilic attack at the carbonyl group C‐5 or deprotonation of the N‐H group may be the first reaction step. 1H NMR spectroscopy is best suited to detect incorporation of initiator fragments. In the case of primary aliphatic amines quantitative endgroup analyses may even allow the calculation of the average degree of polymerization (DP). In the case of base‐initiated polymerization the formation of N‐acyl‐NCA endgroups or the incorporation of the basic initiator is detectable. Furthermore, the role of electrophilic co‐catalysts, such as isocyanates or N‐acyl‐NCAs, can be elucidated. 13C‐ and 15N NMR spectroscopy are better suited than 1H NMR spectroscopy for stereosequence analyses of poly(D,L‐amino acid)s. The results of both methods agree in that primary amine‐initiated polymerizations of D,L‐NCAs yield nearly random stereosequences. Trialkylamine initiated polymerizations of α‐helix forming D,L‐NCAs favour the formation of isotactic blocks, whereas in the case of non‐helicogenic NCAs (e.g. D,L‐Val‐NCA) syndiotactic blocks are preferentially formed. 15N NMR spectroscopy also enables the sequence analysis of binary copolypeptides, and in favourable cases even ternary copolypeptides can be analyzed. 13C NMR crosspolarization/magic angle spinning (CP/MAS) spectroscopy of solid polypeptides enables the qualitative and quantitative determination of their secondary structure. Such investigations revealed that primary amine and tertiary amine‐initiated polymerizations may yield different ratios of crystallites built up by β‐sheets or α‐helices and thereby bimodal molecular weight distributions (MWDs).
Polymerization of propylene oxide by activated monomer mechanism. Suppression of macrocyclics formation
Authors: Wojtania Melania , Kubisa Przemyslaw , Penczek Stanislaw 
Published: March 2011

AbstractEvidence for the activated monomer (AM) mechanism operating in the polymerization of propylene oxide (PO) initiated with HBF4 is presented. The contribution of AM route of propagation is the highest and formation of cyclic oligomers mostly suppressed when monomer concentration is low enough. This was achieved by slowly adding PO to the reaction mixture, as previously proposed on the basis of kinetic considerations.
Cyclic oligomers content in anionic poly (ϵ‐caprolactam)
Authors: Biagini Emilio , Costa Giovanna , Russo Saverio , Turturro Antonio , Riva Fernando , Rovida Camillo 
Published: March 2011

AbstractThe influence of initiator and activator concentrations on the anionic polymerization of ϵ‐caprolactam and, in particular, on the methanol – extractable fraction of the final polymer has been widely studied. Due to the increasing interest of this polymerization in the field of reaction injection molding (RIM) technology, a thorough investigation has been also carried out to find the best experimental conditions for this reaction in the mold. The effect of postpolymerization annealing on the overall amount of low‐molecular mass substances, among which cyclic oligomers, has been evaluated. Thermal properties as well as crystallinity of the resultant materials have been examined. A comparison with literature data is given; the suggested correlation between the amount of the oligomeric fraction and the molecular arrangement of the polymer in the solid state is discussed.
Effect of ring‐size in cationic polymerization of cyclosiloxanes. D6‐polymerization initiated by trifluoromethanesulfonic acid
Authors: Gobin C. , Masure M. , Sauvet G. , Sigwalt P. 
Published: March 2011

AbstractCationic polymerization of dodecamethylcyclohexasiloxane (D6) initiated with triflic acid at 20°C in CH2Cl2 shows a stationary concentration of active centres. This has permitted the measurement of kpx [Pn*] for the various Dx cyclics, and of the ratios of propagation rate constants kp5/kp4 ∼ 2,2 ± 0,4 and kp6/kp4 ∼ 5,8 ± 1,2. On the other hand, the back‐biting rate constants were not significantly different for various cyclics formation (k4 ∼ k5 ∼ k6). These values have been compared with those obtained from D4 and D5 polymerizations.
Anionic polymerization of cyclosiloxanes with cryptates as counterions: New results
Authors: Hubert S. , Hémery P. , Boileau S. 
Published: March 2011

AbstractA kinetic study of the anionic polymerization of hexamethylcyclotrisiloxane ((CH3)2SiO)3 (D3) was carried out in toluene with the cryptate Li+ + [211] as a counterion. The kinetic order with respect to the living end concentration was found to be equal to 1, and the propagation rate constant relative to cryptated ion pairs was determined at several temperatures between −20 and +20°C. The corresponding activation parameters were calculated : Ep = 9.8 kcal.mol−1 and Δ S°t = −20 cal.mol.−1K−1.The reaction of 1,3,5,7‐tetramethyl‐1,3,5,7‐tetravinylcyclotetra‐siloxane ((CH3)(CH2=CH)SiO)4 (D4*) was studied under the same conditions, the reactivity towards silanolate active centers was shown to be very close to that of D3. The rate constants of propagation and depropagation of D4* and of larger cycles D5* and D6* were determined from polymerization experiments on D4*. The propagation rate constants were found to be nearly the same for D4* and D5* : 1.2–1.31.mol−1. s−1, D6* being the less reactive monomer : 0.41.mol−1. s−1. The differences observed in equilibrium constants of the cycles are essentially due to the rate constants of their formation which were found to be 0.42, 0.23, and 0.006 s−1 for D4*, D5* and D6*, respectively.
The cationic grafting of cellulose with 2‐methyl‐2‐oxazoline
Authors: Cheradame H. , Upe Tadjang Ambo , Gandini A. 
Published: March 2011

AbstractGrafting of cellulosic materials, including bleached kraft pulp, has been achieved by electrophilic polymerization. The process involves two steps, (i) the tosylation of the cellulosic substrate by reaction with tosyl chloride, (ii) polymerization of 2‐methyl‐2‐oxazoline in contact with the esterified cellulose. The grafting efficiency was generally in the range of 20 to 50 %, which was attributed to the occurrence of a transfer reaction specific to the cellulose.
The synthesis of polyamine networks using cationic living poly(1‐tert‐butylaziridine)
Authors: van De Velde M. , Goethals E.J. 
Published: March 2011

AbstractPolyamine networks have been synthesized by end‐linking bifunctional living poly‐TBA with polyfunctional nucleophilic reagents. The bifunctional living poly‐TBA was obtained by polymerization of TBA initiated by low molecular weight bifunctional living poly(tetrahydrofuran). The swelling degrees of the networks in several solvents are reported.
Synthesis of stereoregular poly(alkyl malolactonates)
Authors: Arnold Steven C. , Lenz Robert W. 
Published: March 2011

AbstractOptically pure methyl, ethyl, isopropyl, and benzyl (R)‐malolactonate were prepared from (S)‐(‐)‐malic acid and were polymerized in the bulk with tetraethylammonium benzoate as the initiator to yield high‐molecular‐weight, crystalline polymers. The optical purity of methyl and benzyl malolactonate was determined by 1H NMR spectroscopy of the β‐lactone complexed with a chiral europium shift reagent. Enantiomeric excesses of 100% were found (the experimental error was 3%). Optically active poly(β‐malic acid) was obtained from optically active poly[benzyl (S)‐malate] by catalytic hydrogenolysis of the pendent benzyl esters. Ethyl and benzyl (R)‐malolactonate were also copolymerized, and the benzyl esters of the resulting copolymer were converted into carboxylic acid units by hydrogenolysis.
Benzyl esters of optically active malic acid stereocopolymers as obtained by ring‐opening polymerization of (R)‐(+) and (S)‐(‐)‐benzyl malolactonates
Authors: Guerin Ph. , Francillette J. , Braud C. , Vert M. 
Published: March 2011

Abstract(R)‐(+) and (S)‐(‐)‐benzyl malolactonates were copolymerized anionically by using triethylamine and aluminum porphyrin as initiators. Configurational composition of resulting optically active poly(benzyl β‐malate) stereocopolymers depends on the enantiomeric purity in the monomer feed. Stereochemistry during the multistep synthesis starting from aspartic acid enantiomers used as precursors is discussed. It is shown that natural L(+)‐aspartic acid yields (‐)‐poly(benzyl β‐malate) which degrades to L(‐)‐malic acid in alkaline aqueous medium. Configurational structures were investigated by 13C NMR (75.47 MHz) and splittings of stereosensitive resonances are discussed in terms of stereosequence distributions. Results show that stereocopolymerization proceeds through random addition of chiral repeating units according to Bernoullian statistics. In order to exemplify the effect of enantiomeric composition on physical properties, thermal characteristics have been investigated by DSC for the whole series of stereocopolymers. Samples with more than 70% (S) or (R)‐units are semicrystalline. Melting temperature and crystallinity increase with stereoregularity.
Aspects of epoxy resin curing reactions
Authors: Barton John M. 
Published: March 2011

AbstractThe progress that has been made in establishing the mechanism of the curing reaction between epoxides and amines, particularly through the use of calorimetric methods (DSC), is discussed. A novel application of tritium‐labelled compounds to the study of the reaction of epoxides with imidazoles is also presented. The radiochemical method has produced an enhanced understanding of the reaction mechanism and has given kinetic data in good agreement with DSC measurements.
Network structure and plasticization of epoxy‐based resins
Authors: Apicella A. , Nicolais L. 
Published: March 2011

AbstractThe sorption behaviour of water molecules in epoxy‐based thermosetting networks is discussed and related to the modifications of their properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) studies, and dynamic mechanical analyses.Three modes of moisture sorption are assumed: increase in the free volume of the system, hydrogen bonding onto hydrophilic groups present in the network and adsorption onto the surfaces of “holes” which define the excess free volume of the glassy structure. The less stiff Diglycidyl ether of bisphenol‐A (DGEBA) systems have no appreciable sorption via hydrogen bonding, but rather most of the moisture absorbed is due to the free volume increase and adsorption in the “holes”. On the other hand, the stiffer Tetraglycidyl Diaminodiphenyl Methane (TGDDM) systems absorb more moisture through significant hydrogen bonding rather than by the free volume increase. High plasticizations, evident as Tg depressions by 30 to 80°C, are possible being experimentally observed for the stiffer TGDDM resins.Relationships derived from the free volume theory or the classical thermodynamic treatment may be used to describe the dependence of Tg on the composition of miscible blends.
New aspects on intrinsically conducting organic systems and their synthesis
Authors: Naarmann Herbert 
Published: March 2011

AbstractOrganic polymer films with intrinsic conductivity can be produced in a continuous process directly from the monomers by anodic oxidation.This paper describes the synthesis, the scope available for variation in the process, and the main properties of the new polymers.Electrochemical oxidation, e.g. of pyrrole to polypyrrole, is a new polymerization principle that differs essentially from those adopted for classical plastics, i.e. radical or ionic polymerization and polyaddition or polycondensation techniques.It is not only the principle underlying the synthesis that differs, and the properties of the new polymers are unusual.
Electrooxidation of aromatics to polymer films
Authors: LaCroix Jean‐Christophe , Diaz A. F. 
Published: March 2011

AbstractThis report describes the electrochemical preparation and properties of polyaniline films prepared on a bare platinum electrode and on electrodes precoated with a thin film of inert polymer. Films were prepared and studied in several aqueous acid electrolytes including sulfuric, hydrochloric, nitric, trifluoromethylsulfonic, hydrofluoric and trifluoroacetic acid. It is observed that both the concentration and nature of the acid influence the kinetics of the switching reaction. In the more acidic solutions, the reaction has at dependence and depends on the movement of a front across the thickness of the film. In the less acidic solutions, the reaction has a t1/2 dependence and depends on the diffusion of ions in the film. The same response is observed for the oxidation and the reduction reaction. Polyaniline is also electroactive in other various nonaqueous solvents, such as, alcohols, acetic acid and acetonitrile, and voltammograms with well defined waves result when solution contains both organic salt and protic acid. Polyaniline was also prepared on a platinum electrode coated with an inert polymer film such as polymethylmethacrylate (PMMA). The resulting polymer blend is electroactive and the switching reaction is slower than for polyaniline formed on a bare platinum electrode. Finally, a brief description is given of electroactive polyaniline films which can be prepared by polymerization of aniline in a glow discharge.
In‐situ IR spectra of polypyrrole layers on gold electrodes
Authors: Daroux M. L. , Yeager E. B. , Kalaji M. , Cuong N‐H , Bewick A. 
Published: March 2011

AbstractElectrochemically modulated infrared spectroscopy (EMIRS) has been used to study the changes occurring in polypyrrole films during electrochemical oxidation and reduction. Films containing perchlorate, tetrafluoroborate and ferrocyanide counterions have been studied in both aqueous and nonaqueous electrolytes. With the EMIRS technique it has been possible to detect electrochemically produced changes in the polymer backbone, in the counterion species and in incorporated solvent.
The ionic mechanism of the electrochemical doping of poly (3–methylthiophene) studied by secondary ion mass spectroscopy (SIMS)
Authors: Chao F. , Baudoin J. L. , Costa M. , Lang P. 
Published: March 2011

AbstractThe concentration profiles of C104− and Li+ into the poly(3‐methylthiophene) structure were referred to the 3‐methylthiophene concentration for several doping levels during the doping and the undoping processes. The ion amount is very different in the polymer bulk and in a surface region of about 150 Å thickness. The cation is shown to play a role in the first step of the undoping mechanism. The paired ions concentration was determined and an actual doping ratio could be deduced which is different from that calculated by coulometry.
Preparation of polymer phthalocyanine electrodes and their electrochemical properties
Authors: Wührle Dieter , Schumann Bernd , Schmidt Volker , Jaeger Nils 
Published: March 2011

AbstractPhthalocyanine coated electrodes are of interest due to their high electrochemical and electrocatalytical activities. Several possibilities to prepare electrodes coated by polymeric phthalocyanine and its precursor are described. Examples of electrochemical (reduction/reoxidation of the films) as well as electrocatalytical properties are presented.
Electrocatalytic aspects of electrogenerated polymer layers
Authors: Barendrecht E. , Elzing A. , Janssen L. J. J. , van der Putten A. , Visscher W. , Vork F. 
Published: March 2011

AbstractTwo main aspects of electrocatalysis of electrogenerated polymer layers (polypyrrole in this case) are presented here. The first aspect concerns the electrogenerated conducting polypyrrole layer as such; i.e. its preparation with built‐in electrocatalysts, like Pt or metal‐organic complexes. Its properties are discussed in terms of their real electrocatalytic behaviour, viz. their turn‐over numbers. The second part deals with specific studies like:‐ the anodic oxidation of hydrogen with built‐in Pt, and,‐ the cathodic reduction of oxygen with Co and/or Fe‐phthalocyanines.The theoretical model predicts rather well the experimental behaviour.
Poly(phenylene oxide); electropolymerization on mild steel and anticorrosive properties of the layer: A new corrosion test
Authors: Otero T. F. , Ponce M. T. , Jiménez Y. J. 
Published: March 2011

AbstractThe electropolymerization of phenyl salicylate by cyclic potential sweeps over mild steel gives rise to the formation of a poly(phenylene oxide) (PPO) film. In order to study the anticorrosive properties of PPO a new rapid corrosion test has been devised.
Electrocoagulation of waterborne polymers in the presence of carbon black
Authors: Beck Fritz , Guder Harald 
Published: March 2011

AbstractElectrodeposition of paint is an electrochemical process, starting from water‐borne polymers. The electrode reactions are water decomposition, leading to diffusion layers of an extreme pH. Coagulation of polymers proceeds in these layers as an acid / base reaction rather than as a direct discharge of macroions at the electrodes. The electrodeposited film behaves like a weak acid or alkaline ion exchanger. Under polarization, high electric field strength leads to charge separation and the formation of a double space charge. Current / voltage‐behavior is nonlinear. The mechanism of charge transport is purely ionic. Resistivities are in the order of p = 108 Ohm·cm in the wet film. The stoved film is an insulator. Electrodeposition of a second film is impossible. However, electrodeposition of the primary film in the presence of dispersed carbon black, studied in detail for the first time, leads to an appreciable electronic conductivity in the stoved film. ρ is in the order of 105 ‐ 107 Ohm·cm even with a carbon black concentration of only a few wt.‐%. This has been explained in terms of a stick percolation model and the preferential formation of transversal carbon black chains in the film. The relatively high resistivities found along these chains is due to the need of electron tunneling through ultrathin polymer films around the polymer wetted individual carbon black particles. Temperature behavior of resistivities, field effect and other proofs are given for this model.For practical application, the most important findung is the possibility of an electrodeposition of a coherent second layer and even of multilayers in the presence of only 1 ‐ 5 wt.‐% of an appropriate carbon black filler.
Preparation and electrochemical behaviour of electrodes coated with glow‐discharge–polymer films
Authors: Doblhofer Karl 
Published: March 2011

AbstractThe electrical parameters of low‐pressure glow‐discharges are discussed with respect to formation of high‐quality organic thin films on conducting substrates. It is demonstrated theoretically and experimentally that ac discharges operated at frequencies of the order of 10 KHz are well suited for producing flawless dielectric films.
The produced coatings are characterized by electrochemical methods and by electron microscopy. The permeability of the film, its relationship with the chemical nature, and the associated electrochemical behaviour are discussed.
Electropolymerization and conductivity of inhibitors with 2–(5–aminopentyl) benzimidazole
Authors: Schultze J. W. , Rolle D. 
Published: March 2011

AbstractPolymer layers of inhibitors are supposed to be electronically and ionically insulating. Potentiostatic investigations of film growth with PAB demonstrated a self‐inhibiting process which is explained by the limiting electron conductivity of the polymer. Correspondingly, the electrode capacity C decreases with film thickness d, but the potential drop extends over a thin inner film only with an effective thickness deff << d. These results are consistent with the decrease of the current density i of electron transfer reactions. The long‐time behaviour of the films is more complex since ions can slowly diffuse into the film. Small ions, like protons, and molecules, like water, can rapidly move through the film. Hence, oxide formation can take place at the metal/PPAB interface. Conductivity data are estimated.
Electrochemical and spectroscopic characterisation of structural reorganisation in N, N′–dialkylpyridinium cation radical deposits
Authors: Bewick A. , Cunningham D. W. , Lowe A. C. 
Published: March 2011

AbstractThe electrochemical reduction to form a deposit of the radical cation salt for a series of n‐alkyl asymmetrically substituted viologens and the corresponding anodic oxidation processes have been investigated using electrochemical methods in in situ uv‐visible reflectance spectroscopy. Particular attention was focussed on the nature of the restructuring involved in the ageing of the deposit. The use of both p‐ and s‐polarised radiation clearly showed that initially the viologen units were deposited with the major molecular axis parallel to the electrode and on ageing they reorganised into a preferred orientation perpendicular to the electrode. The viologens with the larger substituents were initially deposited as aggregates of mixed micelles containing both cation radical and dication units. The latter were reduced at a well defined potential, the process being seen as a highly‐reversible sharp current spike on the linear sweep voltammograms.