bluuebunny/crossref_metadata_2025 huggingface dataset:
Multicomponent free‐radical polymerization in batch, semi‐ batch and continuous reactors
Authors: Hamielec A. E. , MacGregor J. F. , Penlidis A.
Published: March 2011

A practical methodology for the computer modelling of multicomponent free radical polymerizations for solution and emulsion systems has been developed. The approach is general providing a common model framework which is applicable to many comononer systems. Model calculations include conversion of the monomers, multivariable distributions of concentrations of monomers bound in the polymer chains and molecular weights, long and short chain branching frequencies, chain microstructure and crosslinked gel content when applicable. Diffusion‐controlled termination and propagation reactions are accounted for using the free‐volume theory. When necessary, chain‐length‐dependent diffusion‐controlled termination may be employed.

Kinetic parameters have been measured and are available for the following binary comonomer systems: styrene/acrylonitrile, p‐methylstyrene/acrylonitrile, p‐ methylstyrene/styrene, p‐methylstyrene/methyl methacrylate and styrene/butadiene. Various comononer systems will be used to illustrate the development of practical semi‐batch and continuous reactor operational policies for the manufacture of copolymers with high quality and productivity.

It should be mentioned that these comprehensive polymerization models may be used by chemists and chemical engineers to reduce the time required to develop new polymer products and advanced production processes for their manufacture.
Continuous free radical polymerization in disperse systems
Authors: Reichert K. H. , Moritz H. U.
Published: March 2011

Continuous free radical polymerization in disperse systems was performed in a laminar stirred tubular reactor which is a novel reactor type with narrow residence time distribution in the laminar flow regime. The residence time distribution of such a reactor can be modelled by very simple dimensionless equations containing the axial and radial Reynolds numbers of the reactor at operating conditions. In such a reactor of pilot plant scale the continuous free radical polymerization of acrylamide in emulsion and of vinyl acetate in suspension was studied with respect to conversion and performance of reactor. For modelling the conversion of polymerization the segregation and the dispersion model were used and the results compared with experimental data. Both are suitable models for modelling the upper and lower limit of conversion of micro or macro mixed polymerizations. The vinyl acetate polymerization was also investigated with respect to the breadth of the molecular weight distribution of the polymer formed in batch, continuous segregated, and continuous micro mixed reactors. Models were developed employing a complex kinetic scheme including transfer reaction to polymer and terminal double bond polymerization. Simulation results showed that the molecular weight distribution order in the different reactor types is not fixed, but a function of reactant concentrations and importance of chain branching. The simulations are compared with experimental data.
Free‐radically initiated polymerisations for reaction injection moulding (RIM): Some observations on polymer blends involving poly(methyl methacrylate) as one of the components
Authors: Armitage P. D. , Coates P. D. , Johnson A. F. , Hill S. , Hynds J. , Leadbitter J. , Myktiuk J.
Published: March 2011

The rapid growth of interest in reaction injection moulding (RIM) and reinforced reaction injection moulding (RRIM) has focused attention on polymerisation reactions which can generate useful solid polymeric mouldings with moulding cycle‐times of less than three minutes. Free‐radically initiated polymerisations have long been used in reactive processing, for example, in the casting of acrylic sheet materials and for the cure of polyester resin, but the overall polymerisation times for these reactions has been relatively long. Adapting existing free‐radical polymerisations for RIM and RRIM technology raises many interesting chemical, kinetic and thermodynamic problems. We have been exploring the use of radical processes for very fast processing techniques such as RRIM using a novel computer controlled and monitored RRIM machine developed in our laboratories. Both polyester and acrylic based materials have been reactively processed to give 2–4 kg plaque mouldings in cycle‐times of less than two minutes. Of particular scientific interest are polymer blends and interpenetrating polymer network systems (IPNs) (where one of the concurrent polymerisations is initiated by a free radical mechanism) since these systems give considerable scope in the design of product properties through composition. The principles of reaction injection moulding are briefly described together with some experimental results obtained for an acrylate/polyurethane composite material given emphasis to fundamental aspects of radical polymerisation reactions raised by the need for very rapid and complete conversion of the methyl methacrylate component.
Reactions of carbocations with carbanions through coordination and single electron transfer. Heterolysis and homolysis of carbon‐carbon bonds
Authors: Arnett E. M. , Whitesell L. G. , Amarnath K. , Cheng J. P. , Marchot E.
Published: March 2011

Carbocations, carbanions and free radicals are the most important reactive intermediates in organic chemistry and the majority of bond‐forming and bond‐breaking reactions involve their participation at some stage. We will review briefly our studies, over the past five years, of the direct coordination reaction between carbocations and carbanions to form covalent bonds in solution. We have gathered considerable thermodynamic and kinetic information for this reaction.

Particular emphasis will be placed on recent work on the measurement and analysis of heterolysis energies. Heterolysis is the reverse of the coordination reaction and we have obtained heterolysis energies in solution for over 160 bonds by measuring the heats of reaction between several resonance‐stabilized carbocations and a variety of carbanions, oxyanions, nitranions a thiophenoxide ions in solution. The results are correlated by very simple equations so that heats of heterolysis may be predicted with considerable precision from readily available data.

Carbocations and carbanions can also react by electron transfer to form free radicals. We will describe recent experiments which demonstrate that under appropriate conditions all three types of reactive intermediates can coexist at equilibrium in solution with the electrons shuttling between the three different species.
Identification of some carbocationic active species: Structure and stability relationship
Authors: Sigwalt P. , Matyjaszewski K. , Moreau M.
Published: March 2011

The nature and the stability of the various types of propagating species involved in cationic polymerization of ethylenic monomers are examined. After a short discussion of the evidence for and against the presence of covalent species in styrene polymerization, recent data about the identification of carbocationic active centres involved in the polymerization of para‐substituted α‐methyl‐styrenes are given. Carbenium ions were generated in methylene chloride either by reaction of the p‐substituted cumyl chloride with SbF5 or by reaction of the monomer with trifluoromethanesulfonic acid (HA). They are stable around −70°C, but some of them give secondary reactions at higher temperature. The various types of species were identified by 1H NMR correlated with UV spectroscopy.

For the p‐tert‐butyl derivative, monomeric cations remain stable at −70°C (and even at higher temperature) while oligomeric ones are less stable, giving indanic derivatives. With p‐methoxy‐α‐methylstyrene, the monomeric, dimeric and trimeric cations are stable at −63°C but give indanic derivatives at −40°C and above. For both monomers, monomeric cations show a single maximum at 350 or 367 nm with a high absorption coefficient (≁ 30000). In the presence of an excess of monomer, a bathochromic shift of this maximum (≁ 15 nm) is observed, together with the appearance of a new (smaller) maximum around 480 nm. The presence of these two maxima could be correlated with that of “isomerized” species, some of which could be identified by NMR. The possible occurrence of a similar situation with other monomers and particularly with p‐methoxystyrene is discussed.
Mechanisms of cationic polymerizations of lactones
Authors: Kricheldorf Hans R. , Sumbél Movita‐Verena
Published: March 2011

It is demonstrated by means of 1H NMR spectra in combination with IR spectra that the reaction of δ‐valerolactone with an alkylating reagent results in alkylation of the exocyclic oxygen. The propagation of the resulting cyclic dioxocarbenium ion involves cleavage of the alkyl‐oxygen bond. Initiation and propagation mechanisms induced by Lewis acids such as boron bromide, aluminum bromide, titanium(IV) and zirconium (IV) bromide, tin(IV) bromide and zinc bromide are discussed. It is demonstrated by means of IR and NMR spectroscopy that complexation of the lactones at the exocyclic oxygen is followed by cleavage of the alkyl‐oxygen bond and halogen transfer, so that ω‐bromocarboxylic acids are obtained (after hydrolytic work up). In the case of aluminum, tin and zinc the intermediately formed metal‐oxygen bond initiates rapid polymerization via a nonionic insertion mechanism which is characterized by cleavage of the acyl‐oxygen bond.
Cationic polymerization and copolymerization of lactams and lactam derivatives
Authors: S̄ebenda Jan
Published: March 2011

Lactams and lactam derivatives may be polymerized by various types of processes, but only the cationic mechanisms provide suitable pathways for the polymerization of all types of lactam monomers. Therefore, the cationic polymerization is predestinated for the synthesis of their copolymers. Random copolymers can be obtained even if the rates of homopolymerization of comonomers differ by several orders of magnitude, either by transacylation of block copolymers, or in a new process designated as polymerization with transient chemical activation. This process is operative e.g. in the copolymerization of an unsubstituted and an N‐acylated lactam. It implies N‐acylation of the unsubstituted lactam by the polymer of the N‐acylated one, followed by the incorporation of the activated monomer and subsequent deacylation of the incorporated monomer unit.
Developments in the design and applications of novel thermal and photochemical initiators for cationic polymerization
Authors: Crivello J. V. , Lee J. L. , Conlon D. A.
Published: March 2011

Since their discovery in our laboratories as novel photo and thermal initiators for cationic polymerization, diaryliodonium and triarylsulfonium salts have been the object of considerable investigation in our laboratories as well as in a number of other academic and industrial research groups. Recent work in our laboratory has focused on several major themes which will be the topics of this presentation. These include; the synthesis of new photoinitiators with higher photosensitivity, the preparation of polymer bound photoinitiators, the preparation of new cationically polymerizable monomers with high reactivities and lastly, the use of onium salt induced photo and thermally induced cationic polymerization in a number of practical applications.
The role of sterically‐hindered pyridines in cationic polymerization
Authors: Gandin Alessandro , Martínez Armando
Published: March 2011

A brief survey is given of the syntheses, physico‐chemical properties and reactivity of sterically‐hindered pyridines (SHP). Then a more detailed analysis is devoted to the specific role of these peculiar Lewis bases in the elementary steps of cationic polymerization. The existing literature is critically reviewed and new results are presented and discussed. The unique features of hindered pyridines and their usefulness in both mechanistic studies and practical issues related to cationic polymerization are emphasized.
Cationic reactivation polymerization of vinyl monomers
Authors: Heublein G. , Spange S. , Ulbricht A.
Published: March 2011

The oationio polymerization of strong π‐donor monomers has been investigated, where initiation takes place with triphenylmethylium picrate and picric acid, respectively. In the case of p‐methoxystyrene the polymerization runs via aggregated species, where monomer and picric acid stabilizes the propagating intermediate state. The transfer‐suppressed polymerization oan be reactivated after monomer consumption. The mechanism of IBVE polymerization runs similar, however, by side reactions double bonds can be introduced into the polymer chains and chains can be terminated by water under formation of aldehyde groups. NVC polymerization proceeds via freely solvated ions, which results in relative broad MWD. The polymerization of NVC and p‐methoxystyrene initiated with cationogenes involving nucleophilic counterions, leads in the presence of AEROSIL to increased molecular weights and narrow distribution, in comparison with the polymerization under same conditions in solution.
Characterization of the active centers in the cationic polymerization of p‐substituted α‐methylstyrenes
Authors: Lenz Robert W. , Faullimel Jean G. , Jonte J. Michael , Fisher Danilella J.
Published: March 2011

Polymer tacticity, molecular weight and molecular weight distribution were used as the basis for characterizing the type of active centers present in the cationic polymerization α‐methylstyrene monomers. The affect of reaction solvent polarity and the resonance effects of para‐substituents were used to deduce the nature of, and changes in, the ion pair character of the carbocation active center. For this purpose, the polymer yield, tacticity and molecular weight parameters were determined in the cationic polymerization reactions of p‐chloro and p‐fluoro‐α‐methylstyrene. The dielectric constant of the reaction medium was varied by using mixtures of methylene chloride and either hexane, a non‐solvent for the polymers, or toluene, a good solvent for the polymers. For both solvent systems, the yields and molecular weights of the polymers from both of the monomers were strongly effected by reaction time and solvent composition. Also, for both monomers, tacticity did not change with reaction time, and for the p‐fluoro monomer tacticity was constant with changes in reaction solvent composition in both mixed solvent systems. In contrast, the tacticities of the polymers from the p‐chloro monomer decreased with increasing amounts of the non‐polar solvent in the mixture. The tacticity effects induced by reaction solvent changes are interpreted on the basis of the electronic effects of the para‐substituents on changing the ion pair character of the carbocation active center. The effect of solvent composition on polymer yield and molecular weight may be a function of changes in the rates of initiation, propagation and monomer transfer, with the latter two also determined by the ion pair character of the carbocation active end group.
The cationic oligomerization of C10 fischer‐tropsch olefins and of 1‐decene
Authors: Dressier F. H. , Vermaire S.
Published: March 2011

This paper describes findings on the cationic oligomerization of unrefined C10 cuts obtained from Fischer‐Tropsch products and of 1‐decene as a model olefin.
Technical developments in polyoxymethylene from an industrial point of view
Authors: Cherdron Harald , Burg Karlheinz , Kloos Friedrich , Reske Eckart , Sextro Günter
Published: March 2011

The attempt is made to indicate the future industrial developments in the field of polyoxymethylenes. As far as the process development is concerned, the development of a dehydrogenation route from methanol to formaldehyde or trioxane without the formation of water would be an economical breakthrough. The major product developments are in the area of copolymers with defined sequence length, of blockcopolymers, of blends and of fibrids.
Application of isobutylene telechelics in vulcanizing systems
Authors: Musch R.
Published: March 2011

The application of the “inifer technique” introduced by J.P. Kennedy et al. for the preparation of polyisobutylene (PIB) with two reactive end‐groups results in a new range of functionalized polymers. These products can be blended with polymers to improve the network structure. This presentation deals with the preparation of PIB‐telechelics, their characterization and their application in combination with polychloroprene. During the mixing step we observed an improved processibility of polychloroprene based on the plastifying efficiency of these telechelics. The vulcanization conditions are described under which vulcanization with improved technical properties can be achieved, in summary, the addition of 10–30 parts PIB improves the low temperature flexibility, the weathering and ageing resistance of the polychloroprene vulcanizates. The use of these blends in various fields of application is explained.
Cyclic oligomer formation in the copolymerization of isoprene with isobutylene
Authors: Kuntz I. , Powers K. W. , Hsu C. S. , Rose K. D.
Published: March 2011

The formation of trace amounts of cyclic oligomers in the copolymerization of isoprene with isobutylene has been studied using mass spectrometry and NMR. Two major products are detected with empirical formulas of C13H24 and C21H40. The C13H24 material is identified as 1‐isopropenyl‐2, 2,4,4‐tetramethylcyclohexane. The C21H40 substance is postulated to be a structurally related cyclohexane derivative. The mechanism for the production of such materials is discussed.
Activated esters in the cationic polymerization of styrenes
Authors: Matyjaszewski Krzysztof
Published: March 2011

Cationic polymerization of styrenes initiated by protonic acids can proceed via covalent intermediates. Calculations of the charge distribution in these species show low probability of transfer reactions. Macromolecular and model covalent species in the perchloric acid initiated polymerization of styrene have been directly observed by NMR. Esters formed with triflic acid are very reactive and participate in Friedel‐Crafts alkylation at −78 °C. Acetates become active only in the presence of protonic and Lewis acids. 1‐Phenylethyl trifluoroacetate activated with the parent acid reacts with styrene faster than the acid does. The racemization of the optically active ester is faster than its incorporation indicating an ionic mechanism of propagation in this system. Activation by Lewis acids proceeds by the reversible formation of complexes. Some systems yield polymers with low polydispersity.
Telechelic tetrahydrofuran
Authors: Kress H.‐J. , Stix W. , Heitz W.
Published: March 2011

Condensation polymers with block structure are stable only if one of the constituent blocks is stable against reactions like transesterification, transamidation, etc. This stable block must have a pure CC chain which may be interrupted by ether, sulfide or sulfone linkages. It must be strictly bifunctional in order to be no limiting factor for the molecular weight in the synthesis of blockcopolymers.

If the two functional groups are located at both ends of the polymer chain, we name this product a telechelic. The characterization of telechelics needs the determination of the functionality. Any end group analysis will give only average values. An efficient chromatographic method is necessary to guarantee that bifunctionality is caused by one polymer homologous series.

A number of commercial telechelic polytetrahydrofuranes are strictly bifunctional as shown by GPC1). Two functional end groups can be introduced either by bifunctional initiation and killing the living end groups by a proper nucleophile. The disadvantage of this method is that one mole of an expensive initiator is needed to produce one mole of polymer. The second method to introduce functional end groups uses a proper transfer agent. Only catalytic amounts of initiator are necessary in this case.
Properties of copolymer latexes prepared in inverse microemulsions
Authors: Candau Françoise , Collin Dominique , Kern François
Published: March 2011

The structural and rheological properties of poly(acrylamide‐co‐sodium acrylate) latexes prepared in inverse nonionic microemulsions have been investigated. The formation of stable and optically transparent microlatexes is strongly related to the acrylate content in the feed due to a salting‐out effect of the ethoxylated surfactant. This salting‐out effect determines the optimum HLB value of the blend. The dimensions of the particles are rather low (d < 100nm) with a narrow distribution. The inverse microlatexes which consist of water‐swollen copolymer particles dispersed in an isoparaffinic oil show a newtonian behavior up to high volume fractions (⋍ 50%) and a shear‐thinning behavior for volume fractions above 50%. The presence of charges in the copolymer leads to an apparent close‐packing volume fraction lower than that of 64% predicted for a random packing of hard spheres.
Prediction of the primary particle size distribution in vinyl chloride polymerization
Authors: Kiparissides Costas
Published: March 2011

In the suspension polymerization of VCM insoluble polymer particles are formed inside the vinyl chloride monomer droplets. The nucleation, growth and aggregation of these particles are responsible for the internal morphology and associated properties (i.e. surface area, pore size distribution) of the particulate PVC product. The objective of the present study is to develop a microscopic particle morphology model that can predict the dynamic behaviour of the primary particle size distribution in terms of the controlling process variables (i.e. temperature, initiator concentration, etc.) by formulating a population balance equation to follow the time variation of the primary particle density function from the point of nucleation of basic particles to the formation of particle aggregates. It is shown that model predictions of the primary size distribution are in very good agreement with experimental observations.
Chemical composition distribution of styrene‐methyl acrylate emulsion copolymers
Authors: van Doremaele G.H.J. , van Herk A. M. , German A. L.
Published: March 2011

Thin layer chromatography with flame ionisation detection (TLC/FID) was applied to determine the chemical composition distribution (CCD) of styrene‐methyl acrylate (S‐MA) emulsion copolymers. The reliability of this method was determined using a well defined high conversion S‐MA solution copolymer. The influence of conversion and monomer water ratio on the emulsion copolymer CCD could successfully be described by a model that uses r values determined in solution, and takes into account the monomer partitioning. The samples were prepared in the presence of 1‐dodecanethiol in order to reduce the molecular mass of the copolymer formed. Not only the conversion part of the total copolymer CCD but also the instantaneous (statistical) part appeared to be important.
Copolymer composition control during the seeded emulsion copolymerization of vinyl acetate and methyl acrylate
Authors: Arzamendi Gurutze , Asua José M.
Published: March 2011

The effect of various monomer addition policies on the copolymer composition during the seeded copolymerization of methyl acrylate and vinyl acetate in a semicontinuous reactor was investigated. Four policies were considered. In the first, which is called optimal policy, the reactor was initially charged with all of the less reactive monomer (vinyl acetate) plus the amount of the more reactive monomer (methyl acrylate) needed to initially form a copolymer of the desired composition. Then, the addition of the remaining methyl acrylate was made at a flow rate that ensured the formation of a copolymer of the desired composition. In the second, the initial charge is the same as in the previous case but the time dependent addition rate of methyl acrylate was decomposed into three periods of constant feed rate. In the third, the initial charge is the same as in the previous policies but the remaining methyl acrylate was added at a constant feed rate. In the forth, both monomers were added under starved conditions. In order to calculate the optimal addition policy, the time evolution of the average number of radicals per particle, ñ, is required. The calculation of ñ involves rate parameters which values are usually unknown. Therefore, a semi‐empirical method for the calculation of the time evolution of ñ was developed. It was found that ñ was always greater than 2. For the experimental conditions used in this work, this result suggested that termination in the polymer particles was affected by gel effect. A gel effect function was estimated and then the optimal addition policy was calculated. Comparison between the different processes showed that, for a fixed process time, the copolymer obtained through the optimal addition policy was more homogeneous than that formed when the methyl acrylate was fed in three periods of constant feed rate and even better than the one obtained using a constant feed rate throughout the process. The copolymer quality of the later process is similar to that of the copolymer formed by means of the starved process. Nevertheless, a more homogeneous copolymer composition can be obtained through the starved process when longer process times are used.
Modelling and simulation of emulsion copolymerization of monomers of different polarities ‐ relationship polymerization process ‐ microstucture ‐ properties
Authors: Guillot Jean
Published: March 2011

Accurate kinetic investigations of emulsion copolymerization of monomers of different polarity have allowed to derive reliable mechanisms which appeared to be more complex than usually expected: polymerization in the water phase seems quite general; the solid content ‐ i.e. monomer/water ratio ‐ or, even the pH(when copolymerizing ionogenic monomers) modify the reactivity ratios in emulsion copolymerization; monomer partition is an upmost parameter. However, it is believed that what may be the monomers and the polymerization process, it is possible to model emulsion copolymerization and to develop simulation softwares. These computer simulations then allow to quantitatively compare theoretical behaviour with experimental data and to improve our knowledge of emulsion process. Furthermore, these programs give the sequence distribution of emulsion copolymers and can predict some important properties like the glass transition, which is closely related to copolymer microstructure and hetero‐geneity. Modelling and simulation have been applied to a lot of emulsion copolymerizations and terpolymerizations of various monomers, including some functional monomers.
Recent developments in the functionalization of latex particles
Authors: Pichot C.
Published: March 2011

A survey of the recent literature is given concerning the synthesis and characterization of functionalized latex particles. Two main methods have been particularly considered and discussed: first, the functionalization of latexes by copolymerization of a basic monomer with adding small amount of a monomer bearing a chemical reactive group, with a special emphasis on the kinetics, the distribution of the functional monomer, the surface morphology of latex particles and the optimization of processes; secondly, the use of surface‐active monomers in such reactions which may confer potential advantages (low level of water‐soluble polymers, control of surface charge density) in comparison with the former ones, provided further information can be obtained on their kinetic behavior in emulsion polymerization.
Synthesis of reactive latices by copolymerization of methyl acrylamidoglycolate methyl ether (MAGME) with styrene and butyl acrylate
Authors: Magnet S. , Guillot J.
Published: March 2011

A reactive latex Styrene (S) ‐ Butyl Acrylate (BuA) functionalized with methyl acrylamidoglycolate methyl ether (MAGME) has been synthesized in emulsion and characterized, which can be further crosslinked with other adapted reactive latices. This work deals mainly with kinetics and location of the monomers and with a comparison between experimental and simulated data based on monomer partition and reactivities. The three stages polymerization of hydrophilic MAGME has been quantitatively explained. From the change in overall propagation rate constants and DSC thermograms, it is concluded that particles are structured with a core richer in S and a shell richer in BuA, a huge amount of MAGME being polymerized in the water phase as hydrosoluble polymer strongly adsorbed onto particles and forming a reactive ultimate layer.
Polymer physics and characterization by mechanical measurements
Authors: Cavaillé J. Y. , Perez J.
Published: March 2011

The characterization and the study of the physical properties of polymeric materials need the use of many different experimental techniques. Among them, the mechanical behavior can be considered as a probe able to characterize the molecular mobility if suitable theoretical approaches can relate the macroscopic behavior to microscopic events. Many works have been done using two different types of tests: (i) tests involving stress large enough to induce non‐linear behavior (plastic flow…), (ii) mechanical spectrometry technique or microcreep which involve stress lower than 105 Pa. An attempt have been done to give a unitary description of the behaviors observed under these two conditions. The case of multiphase polymer materials is obviously more difficult, but because the mechanical properties are mainly sensitive on one hand to the behavior of each phase and on the other hand to their geometrical and topological arrangements, it is possible, from mechanical tests, to obtain information about these both aspects.
Influence of chemical heterogeneity on structure and properties of emulsion copolymers
Authors: Zosel A. , Heckmann W. , Ley G. , Mächtle W.
Published: March 2011

When comonomers of different hydrophilicity are copolymerized in emulsion polymerization, a heterogeneous distribution of the polar groups in the resulting latex can occur which is mainly caused by differences in the solubilities of the monomers as well as the polymerization products in the water and the polymer phase. By a combination of various methods, analytical ultracentrifugation of the latices, mechanical spectroscopy, tensile tests and electron microscopy of the latex films, the distribution of the polar groups in the latex, the structure of the latex particles, and the morphology and mechanical behaviour of the latex films have been studied. Films of emulsion copolymers in many cases show a very pronounced two‐phase morphology consisting of the main polymer within the particles and a second hard phase which is concentrated in the interfaces and wedges between the original particles, forming a honeycomb‐like continuous structure throughout the film which has a strong influence on the mechanical properties of the films. When emulsion copolymers are cross‐linked via reactive monomers with a higher degree of hydrophilicity than the main monomers, structurized networks may result with a spatially inhomogeneous distribution of cross‐links. Structure and properties of films from emulsion copolymers are determined by the polymer bulk properties as well as the multiphase structure.
Characterisation of partially‐hydrolysed poly(vinyl acetate)s for use as stabilisers in suspension polymerisation
Authors: Goodall A R , Greenhill‐Hooper M J
Published: March 2011

The surface chemical properties of two partially hydrolysed (98% and 88%) poly(vinyl acetate)s derived from the same parent polymer have been correlated with their ability to stabilise styrene and polystyrene suspensions. The 88% hydrolysed polymer adsorbed more strongly at both the monomer/solution and polymer/solution interfaces to give a thicker adsorbed layer, it also had less tendency to desorb at elevated temperatures. Stability studies showed that both styrene emulsions and polystyrene latex particles were more stable in the presence of the 88% hydrolysed polymer. The results illustrate the importance of the degree of hydrolysis on the stabilising power of these polymers.
Novel aqueous dispersion polymers
Authors: Palluel A.L.L. , Westby M. J. , Bromley C.W.A. , Davies S. P. , Backhouse A. J.
Published: March 2011

Three novel processes for the synthesis of aqueous dispersions of acrylic polymers are described. In each case, stabilisation of the latex is attributed to the presence of water‐soluble polymer chains grafted to the surface of the polymer particles. Acrylic latices comprising grafted, non‐ionic poly(ethylene glycol) (PEG) stabiliser show excellent stability in surface coating applications and superior resistance properties, in both air dried and thermally cured coatings. Latices stabilised with grafted polyelectrolyte are useful in thermosetting paints for spray application.
Kinetics of (CO)polymerizations at the surface of inorganic submicron particles in emulsion‐like systems
Authors: Caris C.H.M. , Kuijpers R.P.M. , van Herk A. M. , German A. L.
Published: March 2011

Hydrophilic TiO2 particles were modified with two different titanates and thus made hydrophobic. “Emulsion” polymerizations were carried out in aqueous dispersions of these particles, stabilized with an anionic surfactant. Polymerization kinetics were determined using a densitometer. The effect of several parameters, like surface modification, surfactant and initiator concentration, and stirring speed on polymerizations were studied. Depending on reaction conditions two competitive polymerizations can take place: one in which polymer is formed at the particle surface and one in which free polymer particles are formed. The TiO2 was modified with a titanate containing a methacrylic acid ester, which was used as a comonomer. Thus a chemical bond between TiO2 particles and polymer was obtained. These polymer encapsulated inorganic particles may offer interesting perspectives in those cases, where a good coupling between particles and matrix is important, for instance in latex paints and in polymer composites.
Tutorial: Thermodynamics of ring‐opening polymerization; Am. Chem. Soc. 199th national meeting, Boston, april 22–27, 1990, 6th international symposium on ring‐opening and cyclo‐polymerization
Authors: Ivin Kenneth J.
Published: March 2011

The ring‐opening polymerization of cyclic monomers shows the characteristic features of any addition polymerization or any physical aggregation process, in particular a ceiling temperature above which the formation of the aggregate (long‐chain polymer), under given conditions of monomer concentration, solvent and pressure, would involve a positive change of free energy and is therefore impossible. Conversely for a given temperature, pressure and solvent, there is an equilibrium monomer concentration below which long‐chain polymer cannot be formed. Cyclic monomers must therefore have a negative free energy of polymerization, under given conditions, if they are to be capable of undergoing a significant extent of ring‐opening polymerization. The effect of monomer structure, including ring size, on thermodynamic polymerizability is discussed, as well as the possibility of copolymerizing monomers which cannot themselves give homopolymers. Examples are given for various possible mechanisms of polymerization.
Synthetic importance and industrial applications of ring‐opening polymerization
Authors: McGrath James E.
Published: March 2011

A survey is provided which demonstrates the synthetic importance and variety of industrial applications that have developed for ring‐opening polymerization. The number of polymers produced this way is quite significant and includes the epoxides such as ethylene and propylene oxide and other cyclic ethers such as trioxane, tetrahydrofuran and the epoxy resins. Other important systems include the polylactams such as polycaprolactam (Nylon 6), the siloxane or silicone materials, polycaprolactone, and cycloolefins such as polynorbornene. Polyoxazolines are newer monomers which can be polymerized via cationic mechanisms to yield either hydrophilic or hydrophobic tertiary polyamides. Thus, the importance of the field is quite well established and continues to grow. Major applications in coatings, fibers, elastomers, adhesives, thermoplastics and thermosets, such as in composite matrix resins, have been developed.
Ring‐opening‐closing alternating copolymerization
Authors: Kobayashi Shiro
Published: March 2011

This paper reports a new copolymerization based on the novel concept, i.e., ring‐opening‐closing alternating copolymerization. The reaction of a cyclic monomer A and a noncyclic monomer B takes place without added initiator or catalyst to give a copolymer of structure having a ring‐opened unit from monomer A and a ring‐closed unit from monomer B in alternating arrangement. As monomer A, five, six and seven‐membered cyclic phosphonites are employed. As monomer B, on the other hand, are used muconic acid and dialdehydes. Combinations of these monomers A and B produced in all cases ring‐opened and closed 1 : 1 alternating copolymers.
Aluminium alkoxides: A family of versatile initiators for the ring‐opening polymerization of lactones and lactides
Authors: Dubois Ph. , Jérǒme R. , Teyssié Ph.
Published: March 2011

Aluminium alkoxides, such as Al(OiPr)3 or Et3‐pAl(O (CH2)2X)p with 1≤p≤3, are very effective in initiating the polymerization of lactones, e.g.ϵ ‐ca‐prolactone and δ ‐valerolactone, and lactides (D,L‐ or L,L‐ isomers). The ring‐opening polymerization proceeds through a “coordination‐insertion” mechanism that involves the selective rupture of the acyl‐oxygen bond of the monomer and its insertion into an Al‐O bond of the initiator. Polymerization is typically “living” and allows block copolyesters with perfectly controlled molecular weight and composition to be prepared. Aluminium alkoxides carrying functional alkoxy groups (X = ‐Br, ‐CH2‐NEt2, ‐CH2‐CH=CH2, ‐CH2‐OC(O)‐C(Me)=CH2…) provide asymmetric telechelic polyesters (end‐groups being ‐X and ‐OH, respectively) and very interesting polyester macromonomers. Coupling the asymmetric telechelic chains via the hydroxyl end‐group ‐ or better its A1 alkoxide precursor ‐ is a straightforward way to the symmetric telechelic polymer bearing the X functional group.
Anionic and pseudoanionic polymerization of ϵ‐caprolactone
Authors: Duda Andrzej , Penczek Stanislaw
Published: March 2011

Anionic polymerization of ϵ‐caprolactone conducted in THF solvent has been compared with polymerizations initiated with aluminium alkoxides. The latter processes have been kinetically analysed as the pseudoionic processes, i. e. with propagation proceeding by insertion. In the pseudoanionic reaction active species are aggregated. The methods of solving kinetic schemes involving aggregation ⇋ deaggregation equilibrium, followed by the chain growth on deaggregated species are described. These kinetic methods have been used to determine the propagation rate constants. The relationships between structures of the growing species and their reactivities have thus been determined.
Preparation of functionalized polycarbonates via ring‐opening polymerization of diverse mixed oligomeric cyclic carbonates
Authors: Brunelle Daniel J. , Shannon Thomas G.
Published: March 2011

The preparation and polymerization of a variety of cyclic oligomeric carbonates containing diverse functionality is described. The preparation of bisphenols containing ether, amide, ester, urethane, etherketone, or ethersulfone functionalities is described. The functionalized bisphenols were converted to dichloroformates via phosgenation, and were subjected to cyclization reactions, forming cyclic oligomeric carbonates containing various functionality. Anionic, ring‐opening polymerization of the cyclic oligomers leads to high molecular weight polymers containing carbonate and other functionality. Depending on the nature of the functionalized bisphenol starting material, the product polymers may be alternating, block, or random copolymers.
Thermal and rheological properties of acrylic copolymers possessing crystallizable polyester side chains
Authors: Scholsky K. M. , Orler E. B. , Bixler K. J. , Stackman R. W.
Published: March 2011

Ring‐opening of ϵ‐caprolactone onto styrene/acrylic acid copolymers was found to occur readily in the presence of a styrene/acrylic acid copolymer at 220 °C. Gel permeation chromatography and extraction experiments utilizing supercritical CO2 suggest that the caprolactone has grafted onto the polymer backbone as polyester side chains. DSC analysis of the modified polymers indicates that the grafted side chains lower the main chain Tg, and when present at sufficiently high levels, contribute crystallinity to the modified materials. Both the melting point and heat of fusion of the modified materials were found to increase as a function of the amount of caprolactone grafted onto the prepolymer. It is unclear whether the formation of crystallites was the result of reaching a critical side chain length, a concentration effect, or a combination of both. The extent of grafting was also found to have a pronounced effect on the melt rheology and rates of crystallization of these materials presumably due to the increased free volume afforded by the polycaprolactone side chains.
Inhibiting or cocatalytic effect of water and other additives on cationic polymerization of cyclodimethylsiloxanes
Authors: Sigwalt P. , Gobin C. , Nicol P. , Moreau M. , Masure M.
Published: March 2011

Cyclodimethylsiloxanes such as hexamethylcyclotrisiloxane (D3) and octamethyl‐cyclotetrasiloxane (D4) have quite different reactivities and generally do not give the same types of cyclic products. An examination of analogies and differences between these two monomers is made in the case of initiation by trifluoromethane sulfonic acid, for both the formation of water during the reaction and the effect of water and other additives. The differences in the formation of water are much less than was expected and perhaps not really significant. A second analogy is that for both monomers, the retarding or inhibiting effect of water is much stronger when it is premixed with the acid rather than mixed in situ, this being attributed in this last case to a possible competition between monomer and water for the first reaction with acid. From the variation of the rates when the mole ratio [H2O]/[Acid] increases, it is concluded that for the initiation reaction water is a retarder or inhibitor for both monomers while for propagation it is an inhibitor for D4 but a very effective cocatalyst for D3. After a comparison of the effects of added water, silanol and triflic esters on propagation reaction and cyclics formation for these two monomers, and a discussion of the possible active centres, it is concluded that the mechanism of propagation should be different for D3.
Synthesis of poly(dimethylsiloxane)‐nylon‐6 diblock copolymers
Authors: Veith C. A. , Cohen R. E.
Published: March 2011

Poly(dimethylsiloxane)‐polyamide‐6 (PDMS‐PA6) diblock copolymers have been synthesized anionically from ω‐N‐acyllactam‐PDMS macroinitiators using newly developed di(tert‐butoxy)‐lithium aluminium hydride catalysts and bulk ultrasonic mixing of the reactants. These copolymers possess high PA6 block molecular weights and good thermal stability in the melt (ca. 250°C) because they do not contain carbamates. Size exclusion chromatography has revealed that traditional catalysts for the ring‐opening polymerization of ϵ‐caprolactam (CPL) such as alkali metal caprolactamates or LiAlH4, significantly depolymerize the PDMS to cyclics (D3, D4) in CPL at moderate temperatures of 100 ‐ 170°C. New coordinating catalysts, produced by derivatizing LiAlH4, reduced the nucleophilicity of the CPL anion but did not interfere with the activated monomer mechanism. These new catalysts eliminated the depolymerization of PDMS to cyclics during growth of the polyamide‐6 block to make the macroinitiator technique viable.
Mechanism of anionic ring‐opening polymerization of silacyclopent‐3‐enes
Authors: Weber William P. , Park Young Tae , Zhou Stephen Q.
Published: March 2011

Anionic ring‐opening polymerization of silacyclopent‐3‐enes has characteristics which are different from those of anionic living polymerizations of 1,3‐dienes. High molcular weights are obtained in most cases but generally with most probable molecular weight distributions Mw/Mn ≅ 2. The polymerization is stereospecific. Poly(1‐sila‐cis‐pent‐3‐enes) are obtained. Ring opening polymerization of 1,1,3‐trimethyl‐1‐sila cyclopent‐3‐ene is found to be regioselective at −78°C to yield a polymer in which cis‐1,4‐isoprene units are joined to dimethylsilylene units almost exclusively in a head to tail orientation. Finally, anionic polymerization of 1‐methyl‐1‐silacyclopent‐3‐ene is found to yield poly(1‐methyl‐1‐sila‐cis‐pent‐3‐ene) of low molecular weight. This permits end group analysis by 1H, 13C and 29Si NMR spectroscopy, signals are observed which are consistent with the presence of 1‐methyl‐1‐silacyclopent‐3‐ene rings. These are probably end groups. A mechanism consistent with the above is discussed.
Block copolymer of 2‐methyl‐2‐oxazoline with silica gel an organic‐inorganic hybrid polymer
Authors: Chujo Yoshiki , Ihara Eiji , Kure Shigeo , Suzuki Keisuke , Saegusa Takeo
Published: March 2011

Ring‐opening polymerization of 2‐methyl‐2‐oxazoline followed by termination with 3‐aminopropyltriethoxysilane produced poly(N‐acetylethylenimine) (polyoxazoline) (POZO) having a terminal triethoxysilyl group. Triethoxysilyl‐terminated telechelic POZO was also prepared by using bifunctional initiators. These silane coupling POZOs were subjected to reaction with silanol groups at the surface of silica gel to modify its surface hydrophilicity. Triethoxysilyl‐terminated POZOs were also subjected to acid‐catalyzed co‐hydrolysis polymerization with tetraethoxysilane by the so‐called sol‐gel method to produce a novel organic‐inorganic hybrid polymer (block copolymer). The hybrid obtained was a homogeneous, transparent, glassy composite material, which showed more hydrophilicity in comparison with that of silica gel without POZO segments. On the other hand, a hybrid polymer consisting of poly(2‐ethyl‐2‐oxazoline) and silica gel showed amphiphilic properties absorbing both water and organic solvents. Pyrolysis of these hybrids at 600°C produced silica having micro‐pores.
Copolymerization of sarcosine‐NCA and l‐leucine‐NCA or l‐phenylalanine‐NCA
Authors: Kricheldorf Hans R. , Tönnes Kai‐Uwe
Published: March 2011

Copolymerizations of sarcosine‐NCA (Sar‐NCA) with leucine‐NCA (Leu‐NCA) or phenylalanine NCA (Phe‐NCA) were conducted under five different reaction conditions. Benzylamine, triethylamine, pyridine and sodium methoxide (NaOMe) were used as initiators. Molar compositions of the resulting copolypeptides were determined by 1H or 13C NMR spectroscopy and reactivity ratios were calculated from copolymerizations stopped at low conversions. Sequence analyses of copolypeptides isolated at high conversions were conducted by means of 13C or 15N NMR spectroscopy. Blocky sequences were found due to a higher reactivity of Sar‐NCA under all reaction conditions. The secondary structure of the solid copolypeptides was characterized by 13C NMR CP/MAS spectroscopy and WAXS powder patterns. The secondary structures are kinetically controlled and change into thermodynamically stable ones upon reprecipitation.
Living and immortal polymerizations of epoxide and episulfide with zinc N‐substituted porphyrin
Authors: Inoue Shohei , Aida Takuzo , Watanabe Yoshihiko , Kawaguchi Ken‐Ichi
Published: March 2011

Zinc complexes of N‐methylated porphyrin are excellent initiators for the living and immortal polymerizations of epoxide and episulfide. A remarkable accelerating effect of visible light is observed in the polymerization of epoxide. Block copolymers from episulfide and epoxide with narrow molecular weight distributions can be synthesized.