bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structures and compositions of copolymers
Authors: Harwood H. James 
Published: March 2011

AbstractAlthough studies on reactions of model radicals with olefins are becoming of increasing importance, most understanding of copolymerization has come from studies on copolymer composition and monomer unit sequence distribution information. A number of models for copolymerization have resulted from such studies. For most copolymerization systems the terminal model provides an adequate representation, but more complicated models which allow for the effects of penultimate units on radical reactivity, for reversibility of propagation steps and for participation of monomer complexes in copolymerization processes must be considered in some cases. Modeling of such copolymerization systems is considerably simplified by computer‐oriented approaches such as matrix–multiplication, Monte Carlo simulation and CSMP or ACSL programming. Recent studies on solvent effects in copolymerizations involving polar monomers indicate that partitioning of monomers between solvent and growing polymer radicals is a very significant phenomenon.
Determination of reactivity ratios in copolymerization
Authors: O'Driscoll K. F. , Reilly P. M. 
Published: March 2011

AbstractFree radical copolymerization of two monomers is usually described in terms of reactivity ratios, only two of which are needed for the simplest (Mayo‐Lewis) model. Other, more complex models (such as penultimate unit effects or complex formation) require more kinetic parameters for a complete description. Published summaries of reactivity ratios list values for about 700 monomers taken from more than 1400 publications. These values represent an enormous amount of descriptive and physico‐chemical information about copolymerization in particular and free radical reactivity in general. It is important that we understand the limits to the numerical correctness of existing data, and that future data gathering be done in a statistically correct manner. In this paper several different linear and non‐linear regression approaches to estimating reactivity ratios are reviewed with emphasis being placed on the Mayo‐Lewis model. Two separate problems are recognized: the first is that of model discrimination, the second that of parameter estimation. It is rare that both problems can be properly treated with a single set of experiments, and we discuss the experimental approaches needed to obtain statistically good results.
Evaluation of alternative models for the mechanism of chain‐growth copolymerization
Authors: Hill David J.T. , O'Donnell James H. 
Published: March 2011

AbstractA general method for discriminating between different models for chain‐growth copolymerization is described. The method is based on the non‐linear least‐squares analysis of variations in the copolymer compositions or sequence distributions with the compositions of the monomer feed mixture. It allows the best values for the reactivity ratios for each model to be evaluated, and their joint confidence regions to be delineated. The method is demonstrated by applications to the copolymerizations of styrene with acrylonitrile and maleic anhydride.
Recent investigations on the rate of binary and ternary copolymerizations
Authors: Braun D. , Czerwinski W. K. 
Published: March 2011

AbstractIn this paper a survey of the actual knowledge on the rate of binary and ternary copolymerizations is given. On the basis of various models of rate equations for binary copolymerizations the classical ternary rate equation of Melville et al. was further developed. New equations were derived for systems characterized by significant viscosity differences between the monomers and the viscosity control of termination is considered. Rate equations presented here were examined by measurements with two monomer systems: styrene/N‐vinyl pyrrolidone/ methylmethacrylate (system I) and diethylmaleate/methylmethacrylate/styrene (system II), both in bulk at 60° C with AIBN as initiator.
Rate of copolymerization in strongly alternating systems: The evidence for the involvement of monomer complexes
Authors: Ebdon John R. 
Published: March 2011

AbstractWork on typical strongly alternating radical copolymerizations is reviewed. Emphasis is placed on measurements of rates of copolymerization as functions of monomer feed ratio, overall monomer concentration and solvent type. Particular attention is paid to the question of whether or not rate measurements can throw light on the detailed mechanisms of alternating radical copolymerizations and especially on whether or not they provide evidence for significant propagation via monomer‐monomer donor‐acceptor complexes. It is concluded that rate measurements alone are not necessarily a good guide to copolymerization mechanisms. A semi‐empirical method is proposed for assessing the likely reactivities of monomer‐monomer complexes; it is shown that this method predicts reactivities for monomer‐monomer complexes which are comparable with some calculated from rate and other data.
Heterogeneous radical polymerization: Reactivity and morphology control
Authors: Guyot A. 
Published: March 2011

AbstractIn the first part of that review, some physical effects are studied, causing changes in the kinetics and mechanism of polymerization reaction when going from an homogeneous solution polymerization to heterogeneous polymerizations. Three main cases are considered: acrylonitrile polymerization in which the polymer is neither soluble nor swollen by its monomer, vinyl chloride polymerization in which the polymer is not soluble in its monomer but is swollen by it, and styrene‐divinylbenzene resin where the apparent reactivity of the second double bond is governed by the syneresis phenomenon. In addition to the Tromsdorff effect on the termination reactions, perturbation due to the heterogeneous character of the reaction may affect the termination reaction by isolating free radicals, propagation reaction by restricting the mobility of the monomer or that of the growing radical through a template effect, or even transfer reactions on the polymer. Via concentration of pendent double bonds are observed inside crosslinked nodules of styrene‐divinylbenzene copolymers.The second part is devoted to the study of morphology. Special emphasis is paid to the case of vinylchloride polymerization where the aggregation phenomena are governed by electrostatic interactions, and also to the case of styrene‐divinylbenzene resins where the formation of the morphology is discussed in terms of critical conversions for phenomena such as appearance of microgels, overlapping of nodules and phase separation. Similarities between porous morphology of PVC and styrene‐divinylbenzene resins are pointed out. Some discussions are also devoted to the supermolecular structures inside small particles in PVC, and also in multistep emulsion copolymerizations.
Fundamentals of carbocation chemistry in alkene polymerization and alkylative or oxidative alkane condensations
Authors: Olah George A. 
Published: March 2011

AbstractSome fundamental aspects of carbocation chemistry are discussed in their relationship to our better understanding of carbocationic olefin polymerization and alkane condensation reactions including those of methane. Whereas trivalent alkyl cations, i.e. R3C+ play the key role in the former, the latter is made possible through the intermediacy of five coordinate carbocations of the CH5+ type. In conventional acid catalyzed reactions carbocations are always in equilibrium with their corresponding olefins, whereas under superacidic, stable ion conditions carbocations can be generated and reacted free of such equilibria. The chemical consequences of these differences are discussed in polymerization, as well as in alkylative or oxidative alkane condensation reactions.
Kinetic and thermodynamic studies of carbenium ion additions towards alkenes
Authors: Mayr Herbert , Schneider Reinhard , Schade Christian 
Published: March 2011

AbstractThe ionisation (Ar2CHCl + BCl3 ⇌ Ar2CH+BCl−4) and dissociation (Ar2CH+BCl−4 ⇌ Ar2CH+ + BCl−4) equilibria of diarylmethyl chlorides in boron trichloride/dichloromethane solution have been studied by conductimetry, photometry and 1H NMR spectroscopy. Small differences in the UV‐vis spectra of diaryl‐carbenium tetrachloroborates, which have been observed in solutions of low and high tetrachloroborate concentration, can be attributed to the formation of 1:1 ion‐pairs in the more concentrated solutions. Low temperature calorimetry was used to determine the heats of addition of diarylcarbenium tetrachloroborates to 2‐methyl‐1‐pentene (Ar2CH+BCl−4 + H2C‐CRR' + Ar2CH‐CH2‐CRR'Cl + BCl3), and it is estimated that the standard free enthalpy of this reaction is greater than 0 for systems with pKR+ > −2.6. Kinetic studies have shown that paired and unpaired diarylcarbenium tetrachloroborates exhibit identical reactivity towards alkenes. A rationalisation for the different situation in carbocationic and carbanionic polymerisation is presented. The rate constants for the initiation of isobutene, styrene and isoprene polymerisation by diarylcarbenium ions have been determined, and it is shown, how propagation rate constants can be estimated from linear free energy relationships.
A new conceptualization in relation to ionic polymerizations
Authors: Saegusa Takeo 
Published: March 2011

AbstractA new systematization is presented for the polymerization reactions in relation to the so‐called “Ionic Polymerizations'. The basis of the new systematization, is the concept of the reaction between “Electrophile” and “Nucleophile”. The reactants are either ions (cation or anion) or dipoles. Polymerization reactions except free radical polymerization and polycondensation are classified into three categories depending upon the reactivity characteristics (electrophilic or nucleophilic) of the propagating species.a. Polymerization via electrophilic propagating speciesb. Polymerization via nucleophilic propagating speciesc. Polymerization via zwitterionsEmphasis is placed on the polymerization reactions which propagate through covalent species having nucleophilic or electrophilic reactivity. By this systematization, several polymerization systems which have been treated as unusual or exceptional cases are thus reasonably categorized.
Chain extension of oligodiols by means of cyclic acetals
Authors: Franta E. , Kubisa P. , Refai J. , Kada S. Ould , Reibel L. 
Published: March 2011

AbstractWe have studied the reaction of 1,3‐dioxolane with trifluoromethanesulfonic acid in the presence of α,ω‐dihydroxypolytetrahydrofurane and α,ω ‐ dihydroxypolystyrene. Besides polymerization of 1,3‐dioxolane we have observed the occurence of a fast coupling reaction between the initial oligodiols. The mechanism has been studied using a monohydroxylated polystyrene and a model compound, 3‐phenyl‐1‐butanol. We have shown that coupling takes places through transacetalization even under the mild conditions used Ethylene glycol is produced and an acetal bridge is formed between oligodiols. Conditions have been found where high‐molecular‐weight polymer is formed through this polycondensation, in the absence of homopoly(1,3‐dioxolane).
Controlled polymerization of silyl vinyl ethers by aldol group transfer polymerization
Authors: Boettcher F. Peter 
Published: March 2011

AbstractSilyl vinyl ethers can be polymerized at room temperature and in high yield by initiation with electrophiles, e.g. aldehydes, in the presence of a Lewis acid catalyst. This polymerization, called aldol group transfer polymerization, is living and permits good molecular weight control. Narrow molecular weight distribution is usually obtained. The silylated polymerization products can be hydrolyzed to poly(vinyl alcohol) and coupled via the reactive end group with other functional polymers to give block copolymers. Other block and graft polymers containing the hydrophilic poly(vinyl alcohol) segment can be obtained by initiating aldol group transfer polymerization with mono‐ or multifunctional polymeric initiators.
Activated monomer mechanism in the cationic polymerization of cyclic ethers
Authors: Kubisa Przemysław 
Published: March 2011

AbstractCationic polymerization of oxiranes proceeds in the presence of hydroxyl groups containing compounds by activated monomer (AM) mechanism, competing with active chain end (ACE) mechanism. According to the AM mechanism, propagation involves reaction of activated (e.g. protonated) monomer molecules with nucleophilic sites in the growing macromolecules. Active species are located on the monomer, and growing macromolecule is neutral; thus side‐reactions, typical for active chain‐ end mechanism, are suppressed. In the polymerization of ethylene oxide (EO) ether oxygen atoms along the chain are more exposed to the attack than in the polymers of substituted oxiranes and also react with protonated monomer. The contribution of these reactions, in comparison with propagation involving hydroxyl end groups, is analysed. The participation of the polymer units is highly restrained for chains with bulky substituents. In the AM polymerization of propylene oxide (PO) and epichlorohydrin (ECH), chain growth proceeds predominantly on the terminal hydroxyl groups. Syntheses of telechelic oligomers and macromonomers, applying the AM mechanism with protonated monomers, are described.
Mathematical modelling of cationic alkene polymerization
Authors: Freyer C. V. , Nuyken O. 
Published: March 2011

AbstractIn recent years progress has been made in mathematical modelling of complicated chemical systems. Simulation of reactions with computational techniques offers an excellent method for testing the extent to which a reaction mechanism is indeed understood.After considering the principles of modelling and its advantages in general we present a new type of modelling of polymerizations and its advantages in particular. This method typically involves time‐stepwise integration of kinetic equations and works at a level in between macroscopic (= conventional kinetics) and microscopic (= molecular statistics). At this “semi‐microscopic” level reactants are discriminated not only by the functional groups but also by the chain lengths. Since this method additionally provides information on molecular mass distribution, better facilities to fit experimental data and, therefore, higher confidence in the accuracy of the model are achieved.With regard to cationic polymerization of alkenes there still is uncertainty of some mechanistic details. Showing the latest developments of our new method specially developed for polymerizations we will discuss our first results. Our objective is to apply the new method for kinetic investigations and to contribute new information on this field.
Covalent and ionic species in cationic polymerizations: Rates of exchange
Authors: Penczek Stanislaw , Szymanski Ryszard 
Published: March 2011

AbstractThe general kinetic scheme of simultaneous propagation on covalent and ionic species is discussed. There are a few ways of interconversion of covalent and ionic species, and at least two different modes of covalent propagation. This is either a direct inclusion with reformation of covalent species or reaction of covalent species with a monomer, giving ionic species, collapsing then into the covalent species and/or propagating ionically.Significance of these processes for the overall kinetics is discussed; rates of exchange covalent ⇌ ionic and covalent + monomer ⇌ ionic are discussed in more detail on the basis of trityl chloride ionization and ester‐ion equilibria in the polymerization of THF and oxepane.
Unsaturated telechelic oligoisobutylenes: Appraisal of the transfer efficiency of some dienes
Authors: Cheradame H. , Razzouk H. , Rousset E. , Gandini A. 
Published: March 2011

AbstractIsobutylene was polymerized in the presence of 1,3‐pentadiene (BF3 initiator) and 2,5‐dimethyl–2,4‐hexadiene (AlEt2Cl initiator) in CH2Cl2. Analysis combining examination of the H (mainly 300 MHz) and C NMR spectra and oxidative cleavage by RuO4 of the copolymers obtained was carried out. Some homopolyisobutylenes (TiCl4 initiator) were synthesized for comparison. The results show that it is possible to account for the structures of macromolecular chain ends by the assumption of hydride or methide transfer. The consequences of this assumption are thoroughly discussed.
New initiators for living cationic polymerization of vinyl compounds
Authors: Higashimura Toshinobu , Aoshima Sadahito , Sawamoto Mitsuo 
Published: March 2011

AbstractLiving cationic polymerizations of vinyl ethers and related vinyl monomers were achieved by stabilizing the propagating carbocation either with a counteranion or with an added base. The following initiating systems, designed on the basis of these two approaches, were found to induce well‐defined living polymerizations, some of which proceeded even above room temperature (+25 to +70°C).(a) Stabilization by a counteranion:magnified image(b) Stabilization by an added base:magnified imageFor the first approach, judicious matching of the stability of the growing carbocation and the nucleophilicity of a counteranion was critical. For the second approach, coordination (or solvation) of the growing end by the added base was the key to the generation of living polymers. The nature of the living propagating species is also discussed.
Synthesis of new functional polymers by living cationic polymerization
Authors: Sawamoto Mitsuo , Aoshima Sadahito , Higashimura Toshinobu 
Published: March 2011

AbstractThis paper covers three major areas of the synthetic applications of living cationic polymerization of vinyl ethers initiated by the hydrogen iodide/iodine (HI/I2) system; namely, the synthesis of (a) pendant‐functionalized polymers, (b) end‐functionalized polymers, and (c) amphiphilic block polymers with a unique structure. In area (a), more than 25 vinyl ethers with a functional pendant were found to undergo living polymerization to give a variety of pendant‐functionalized polymers:magnified imageIn area (b), terminally monofunctional and telechelic polymers (including macromonomers) were prepared by living polymerization using a functional initiating system (CH3‐CHI‐OCH2CH2‐X/I2) and/or by end‐capping of the HI/I2‐initiated living polymer ends with a functional nucleophile (:Nu‐X):magnified imageIn area (c), amphiphilic block polymers of vinyl ethers were obtained and characterized, the hydrophilic segment of which carried highly branched bulky substituents with a large number of hydroxyl groups (six per pendant):magnified image
Emulsion copolymerization kinetics with polar monomers
Authors: Bartoň Jaroslav 
Published: March 2011

AbstractThe multi‐component polymerization of the industrially important hydrophobic and hydrophilic monomers exhibits special features in comparison to the multi‐component emulsion polymerization of hydrophobic monomers. The main difference stems from the partial or total solubility of the hydrophilic monomer in the continuous water phase and in some instances also from the formation of water‐soluble polymer. The chemical and morphological structure of the polymer particles, beside the comonomer partitioning between water and oil phases, is governed also by the reactivity ratios of comonomer pair and by the extent of the mutual miscibility or phase separation of polymeric material of the particle. Compositional (chemical) heterogeneity of the polymer particles is also influenced by different affinity of the polymer (copolymer) to the water and oil phases. Structurally inhomogeneous polymer product results from the simultaneously proceeding polymerization in the water and oil phases. The polymer product represents a mixture of homopolymer (copolymer) formed in the water phase and of the copolymer (sometimes graft copolymer) formed on the surface of the polymer particles or in the interphase surrounding the polymer particle.
Dispersion copolymerization in non‐aqueous media
Authors: Ober Christopher K. 
Published: March 2011

AbstractRecent developments in dispersion copolymerization including particle formation in both polar and nonpolar media are discussed. The effects of stabilizer, reaction medium and initiation rate on particle size and distribution in homo‐ and copolymerization are described, and in particular, processes leading to the formation of monodisperse latices and the crosslinking of these microspheres will be examined.
Basic aspects and recent developments in suspension polymerisation
Authors: Brooks B. W. 
Published: March 2011

AbstractIn suspension processes, polymerisation occurs in a monomer‐containing phase which is dispersed in a continuous liquid phase. Controlled agitation and the presence of drop stabilisers are necessary to maintain the suspension. Temperature control is usually better than that observed in corresponding bulk processes. Polymerisation kinetics are often similar to those which apply to bulk systems but high conversions increase the probability of gel effects. Drop sizes can depend on conditions of turbulence, viscosity and interfacial tension. Correlations for maximum drop sizes are discussed. Drop segregation can affect product quality and reactor design is important. Drop sizes can change with time and particle size distributions may become bimodal. Polymeric stabilisers may be present in both the continuous and dispersed phases. If polymer precipitates inside the drops, the stabiliser can influence the particle morphology. The stabilising action of particulate inorganic solids is not well‐understood. In copolymerisation, cross‐linking may occur. Precipitation of copolymer can be promoted by the use of diluents. Stabilisers can have a role in determining porosity of the final particles. Reactivity ratios may appear to differ from those expected in bulk processes when one or more of the comonomers is appreciably soluble in the continuous phase. Relevant literature is reviewed and topics requiring further work are identified.
Hydrophilic polyelectrolyte gels by inverse suspension
Authors: Trijasson P. , Pith T. , Lambla M. 
Published: March 2011

AbstractThis paper is devoted to the synthesis and characterization of highly hydrophilic polymer gels based on acrylic monomers. These superabsorbant polymeric materials (SAPs) were prepared by polymerization of an aqueous solution of monomers dispersed in a continuous organic phase. This inverse suspension process (I.S) was carried out in cyclohexane, the aqueous dispersed mixture containing acrylic acid, partially neutralised, at a given crosslinker/monomer ratio. The dispersion is stabilized by the introduction of a surfactant like SPAN 80. Due to an almost complete lack of available scientific knowledge, it was necessary to perform a basic study covering the influence of the main parameters driving the behaviour of SAPs, especially maximum swelling and absorption kinetics. Further influence of crosslinking density, initial monomer concentration and process conditions have been studied on the base of a model recipe. These results led to optimisation of swelling and absorption behaviour, using various kinds of monomer species and different polymerization conditions.
Scattering studies of the morphology of copolymer colloidal particles
Authors: Bootle Ceraldine A. , Lye Jill E. , Ottewill Ronald H. 
Published: March 2011

AbstractSmall angle neutron scattering studies have been carried out on copolymer latices prepared using acrylonitrile and styrene. These showed that when one of the monomers was deuterated good contrast in scattering was obtained between the two polymers. In the case of poly(acrylonitrile) ‐ poly(styrene) particles evidence was obtained for a core shell morphology with the poly(acrylonitrile) forming the outer shell.