Polymerisation of butadiene in the presence of carbon tetrabromide

Studies of the polymerisation of butadiene in the presence of carbon tetrabromide in bulk and emulsion systems have shown that in both systems telomers are the first products of reaction. These consist of between 4–10 butadiene units with terminal allylic bromine and tribromomethyl groups. However, the fact that the telomers function as chain transfer agents through the terminal tribromomethyl group to produce diallylic bromine terminated low molecular weight polymers is unique to the emulsion system. Telomers prepared in bulk and emulsion have been isolated, characterised and the kinetics of their formation studied. Kinetic analysis has indicated that at low molecular weights an increase in polymerisation rate with increasing carbon tetrabromide concentration is predicted, but it is postulated that the telomer itself can initiate polymerisation. Telomers formed in either bulk or emulsion have been studied as chain transfer agents in the polymerisation of butadiene in emulsion at 60°C. Polymerisation rate decreases with increasing amount of chain transfer and it is postulated that degradative chain transfer plays a role in the polymerisation. A simplified kinetic scheme for retarded polymerisation has been developed to analyse the results. It is postulated that radical termination is by cross termination of growing polymer radicals with telomer radicals.     

Development of new initiators for polymerisation reactions

The development of simple, stable, and well defined catalyst systems for the initiation of ionic polymerisation is reviewed. The principles involved are illustrated by reference to the use of potassium t-butoxide in dimethyl sulphoxide for initiating anionic polymerisation of ethylene oxide and of the hexachloroantimonate salt of the triphenyl methyl cation for polymerisation of tetrahydrofuran. Other stable organic cations initiate polymerisation via charge transfer complexes and can give rise to cation-radicals as intermediates. It is suggested that related cation-radicals may play a role in lignin biosynthesis.     

Order-disorder transitions in poly(3,4-ethylenedioxythiophene)

The commonly held perception that high conductivity in conducting polymers is linked to a high level of π-stacking order in the material is shown here to be of lesser importance in highly conducting poly(3,4-ethylenedioxythiophene) (PEDT), which has been prepared by chemical vapour phase polymerisation. Despite the fact that there is a highly energetic phase transition about 130 °C (110 J/g), and that this transition corresponds to a loss of the long-range π-stacking as observed in grazing angle XRD, the conductivity remains unchanged beyond the transition and only decreases by a factor of two when heating to above 200 °C. The XRD data suggest that order in two dimension remains above the phase transition measured by DSC and this order is sufficient to maintain a high level of electronic conductivity. Furthermore, as the ligand on the iron salt used in the synthesis is varied, the conductivity of the PEDT varies over two orders of magnitude. These phenomena cannot be explained by different degree of doping or crystallinity and it is proposed that the iron salt has an ordering effect during the vapour phase polymerisation.     

Atmospheric Plasma Deposition: A New Pathway in the Design of Conducting Polymer‐Based Anodes for Hydrogen Fuel Cells

In this study, we explored thin films of nanofibrous functionalised conducting plasma polyaniline (pPANI) with platinum deposited by an atmospheric plasma deposition process for the potential design of anodes for hydrogen fuel cell applications. We observed that the incorporation of such a polymer, characterised by both electronic and ionic conductivity, associated with a catalyst in a 3D porous network, could lead to an increased probability of the three‐phase contact to occur. In this context, aniline was mixed with functionalised platinum nanoparticles and used as the precursor. The role of these functionalised nanoparticles was not only to act as the catalyst for fuel cell purposes, but also as nucleation sites promoting the formation of the nanofibrous pPANI thin film during the plasma polymerisation. The morphology of the thin film was analysed by scanning electron microscopy and the efficiency, in terms of energy conversion, was assessed in a single fuel cell test bench.     

Naphthoylenebenzimidazolone dyes as one-component photoinitiators

The appropriate substituents have been added to a 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one skeleton in order to obtain a one-component initiator system. The absorption, fluorescence, and electrochemical properties of these naphthoylenebenzimidazolone dyes and their usefulness as visible light initiators of free radical polymerisation of trimethylolpropane triacrylate were examined. The initiation efficiency of these dyes was compared with that of the parent 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one in the presence of a coinitiator. Results show that these bifunctional dyes are able to initiate polymerisation without an additional coinitiator. Photopolymerisation studies and the relationship between the rate of polymerisation and the free energy change for electron transfer revealed that, depending on the concentration, initiating radicals are generated via intra- and intermolecular electron transfer.     

Polymerisation by glow discharge electrolysis

A glow discharge passed from a metal anode to the surface of aqueous solutions of acrylamide produces radicals which initiate polymerisation. The yield of polymer together with its relative molecular mass has been examined as a function of monomer concentration and pressure in neutral solutions. The form of the variations can be explained in terms of a simplified reaction scheme. On the basis of the proposed mechanism there are two reaction zones. In the primary reaction zone no polymerisation occurs, the radical concentration being too high. About 0·2% of the radicals escape into the secondary reaction zone to initiate polymerisation, the volume of this zone being about 0·4 cm³.In alkaline solutions the yields and relative molecular masses of the polymers are very low and this is attributed to chain termination by oxygen which rises from the destruction of hydrogen peroxide in alkaline solution.     

ATRP grafting from silica surface to create first and second generation of grafts

Summary (11'-Chlorodimethylsilylundecyl)-2-chloro-2-phenylacetate 2 as an atom transfer radical polymerisation (ATRP) initiator was bound covalently to the surface of silica. ATRP grafting of styrene monomer from the silica surface was achieved and the grafts were detached from the solid particles for analysis. It is shown that after polymerisation of a first generation of grafts and work-up of the thus grafted silica the chain ends of the grafts are still active to initiate a second monomer feed to further chain growth. Received: 17 July 1999/Revised version: 12 December 1999/Accepted: 10 January 2000     

Initiator complexes derived from dichlorobiscyclopentadienyl titanium and alkyl aluminium compounds: IV. Di-isobutyl aluminium hydride

Complexes produced in the reaction of dichloro-biscyclopentadienyl titanium and di-isobutyl aluminium hydride (DBAH) have been studied as initiators for the polymerisation of styrene and characterised spectroscopically. In general the complexes do not initiate and the observed dilatometric contractions can be attributed to a reaction between styrene and DBAH. The limited amount of polymerisation observed can be associated with a radical process involved in the reduction of Ti(IV) to Ti(III).     

Processing of cellular ceramics by foaming and in situ polymerisation of organic monomers

This paper describes studies on a new processing route for fabricating highly porous ceramics. The method is based on the generation of a foam from an aqueous suspension of ceramic powder and the subsequent stabilisation of the structure by in situ polymerisation of organic monomers. The influence of the slip viscosity on the foam volume and stability was determined using concentrated alumina suspensions containing dispersing agents and two commercial foaming agents. The in situ polymerisation of organic monomers led to fast solidification, resulting in strong, porous bodies which could withstand machining. The resulting ceramic foams consisted of a highly interconnected network of spherical cells with densities as low as 6% of theoretical. The distribution of cell size was dependent both on the density of the specimen produced and on the time for polymerisation onset. The size ranged from approximately 30 to 600 μm. Enlargement of cell size to achieve materials of higher permeability was possible through expansion of the foam via pressure reduction before polymerisation. The creation of highly densified struts between the cells led to flexural strengths as high as 26 MPa. ©     

Siloxane modification of polyamides

Polyamide–polydimethylsiloxane block copolymers were made by the BuLi or LiOSi(CH₃)₂OSi(CH₃)₂OLi catalysed polymerisation of hexamethylcyclotrisiloxane terminated by and using this substituted siloxane to initiate the polymerisation of lauryllactam or caprolactam in toluene solvent in the presence of lithium aluminium hydride as the catalyst. One or 2% of the polycaprolactam-polydimethylsiloxane block copolymers were mixed with nylon 6 and discs moulded. The presence of silicone in the surface was demonstrated by determining the critical surface tensions of wetting using ethanol–water mixtures as the contact-angle test liquids. A polylauryllactam–polydimethylsiloxane block copolymer compatible with polyethylene was similarly studied. An important application for such composites is to provide a dry lubricated surface, therefore the kinetic coefficients of friction of steel against these copolymer-treated nylon 6 samples were determined demonstrating at best a reduction to one third that of the untreated control.     

Electroinitiated and radiation-induced polymerisation of epoxycyclohexane

Liquid-state radiation-induced and electroinitiated polymerisations of epoxycyclohexane (ECH) have been investigated. The effect of temperature on the electroinitiated polymerisation rate was also studied. The decrease in monomer concentration during polymerisation was followed by gas chromatographic analysis of electrolysis solutions. The i.r. spectra of the polymers suggested polyether structure. N.m.r. spectra of products indicate that the polymerisation of ECH propagates through the opening of the epoxy rings. Poly(epoxycyclohexane) obtained by both methods are amorphous according to X-ray analyses.     

Synthesis and crosslinking of allyl polyarylmethylenes

Polyarylmethylenes containing allyl unsaturation have been synthesised by the Friedel-Crafts polymerisation of an allyl aromatic monomer and bis(methoxymethyl) benzene. The allyl groups do not take part in the Friedel-Crafts polymerisation. The product can therefore be crosslinked through the allyl unsaturation thermally, or by heating with free radical or cationic initiators. The cationic crosslinking reaction appears to be the most convenient.     

Synthesis and application of dyes derived from benz[cd]indol‐2(1H)‐one as visible‐light‐absorbing polymerisation photoinitiators

Several potential initiators based on benz[cd]indol‐2(1H)‐one dye have been synthesised and evaluated in the radical polymerisation of a system containing trimethylolpropane triacrylate under visible light. Absorption, fluorescence, and phosphorescence spectra and the electrochemical properties of these novel dyes were determined. Owing to the presence of an appropriate hydrogen donor group in their structure, these photoinitiators do not need an extra coinitiator to initiate the polymerisation process. During photopolymerisation they act both as a triplet sensitiser and as a hydrogen donor. The relationship between the polymerisation rate and the triplet‐excited‐state reduction potential suggests that initiating radicals are formed from the triplet state via hydrogen transfer. This mechanism is supported by density functional theory calculations. 8‐Bromo‐6‐[(2‐sulphanylethyl)sulphanyl]benzo[cd]indol‐2(1H)‐one and 8‐bromo‐6‐sulphanylbenz[cd]indol‐2(1H)‐one may be applied as visible‐light initiators of free radical polymerisation to obtain a low‐molecular‐weight polymer.     

Stochastic model for living radical polymerisation of styrene initiated by epoxide radical ring opening

A stochastic model was developed to simulate the polymerisation kinetics and the detailed microstructure of the resulting polymers made by the living radical polymerisation of styrene initiated by epoxide radical ring opening. The model was used to predict monomer conversion, average molecular weight, polydispersity index, and molecular weight distribution as a function of polymerisation time. Simulations were used to explore the effects of rate constant values on chain microstructures and polymer properties and validated with experimental data published in the literature. It was found that some parameters, such as the exchange rate constant, have no significant effect on the polymerisation kinetics, whereas major effects were observed when other rate constants, such as the reduction rate constant, were changed.     

Characteristic intervals in suspension polymerisation reactors: An experimental and modelling study

Suspension polymerisation of methyl methacrylate was carried out as a model to elaborate on the evolution of particle size average and distribution in the course of polymerisation. Four characteristic intervals in the evolution of particle size were identified as: transition, quasi-steady-state, growth, and identification stages. The effects of stabiliser and initiator concentrations, monomer hold up, reaction temperature, and agitation speed on the characteristic intervals, as well as the kinetics of polymerisation, were examined. The transition stage, which has been totally ignored in the literature, was found to have significant effect on the evolution of particle size. The transition stage is shortened by increasing the rate of polymerisation in the drops (either by increasing initiator concentration or using a higher reaction temperature). Increasing the impeller speed and stabiliser concentration will also lead to a shorter transition period. However, the delayed adsorption of the stabiliser on the surface of drops will prolong the transition stage. It is shown that the occurrence of the quasi-steady state depends on the polymerisation conditions. The quasi-steady state occurs only if the balance between drop break up and coalescence can be maintained. This requires a high rate of drop break up within a period of time during polymerisation (i.e., a low rate of polymerisation in the drops by using a low initiator concentration and reaction temperature, a high agitation speed and a high stabiliser concentration). The mechanisms underlying the growth stage are explained in terms of the overall rates of drop break up and coalescence in the course of polymerisation reactions. It is also shown that the onset of growth stage cannot be defined in terms of a critical conversation or viscosity, and it depends on the polymerisation conditions including mixing. The growth stage occurs if drops are not sufficiently stable against both break up and coalescence. The onset of the growth stage is advanced with a decrease in the rate of drop break up (e.g., decreasing agitation speed and stabiliser concentration). The growth stage can be totally eliminated from a polymerisation process if dispersions with a static steady state can be formed. That requires a high concentration of stabiliser, or a low concentration of monomer, to be used. A population balance model, which included the transition stage and the delayed adsorption of the stabiliser, was developed that is capable of predicting the evolution of drop size in the suspension polymerisation.     

Synthese elektrisch leitfähiger polymerer

Synthesis of electrically conducting polymers In the last few years electrically conducting polymers have been a centre of scientific interest. Characteristic of these polymers - e. g. polyenes and polyaromatics - are their conjugated double bonds. The addition of electron donators or acceptors causes by the change from insulator properties to electrical conductivity comparable to that of metallic conductors oxidation or reduction of the polymer backbone. Via complex formation a considerable increase in the electron mobility and electrical conductivity is obtained. The aim of the polymer chemist is the synthesis of electrically conducting polymer backbones. An abundance of synthetic routes is available. In addition to the conventional stepwise synthesis using the Wittig-, Horner or Grignard reactions, polycondensation processes and metal-catalysed polymerisat ion techniques can be employed. Oxidative coupling with oxidising Lewis acid catalysts generally leads to polymers with aromatic or heterocyclic units. The Ziegler-Natta-polymerization of acetylenes to filmbuilding polyacetylenes has found broad acceptance; it represents however only one of the many possible reactions, in which reducing agents in combination with transition metals are catalytically active. The polymers synthesised via this process are made electrically conducting by doping. On the other hand the direct polymerisation process e.g. starting from acetylene or aromatics, using the doping agent or via anodic oxidation e. g. from pyrrole, leads directyl to materials with a high electrical conductivity. This paper contains the most important publication with the exception of the patents in the intensively researched field of the synthesis of aliphatic and aromatic polymers with π-electron-conjugation as well as their doping to highly conducting materials.     

Environmentally friendly coloration of cotton by the UV‐induced photografting of α‐bromoacrylamido dyes

Conventional wet dyeing based on dye diffusion and adsorption in water requires large amounts of salt, time, and energy. α‐Bromoacrylamido dyes are photografted onto cotton at room temperature as an environmentally friendly coloration process. Dye‐originated radicals are produced by the photoscission of the carbon–sulfur and carbon–bromine bonds of the dyes and subsequently abstract hydrogen atoms to generate cellulose radicals which can initiate graft copolymerisation. About 88% of the dyes are polymerised, and the degree of polymerisation is estimated to be 12.7 or more, which was substantiated by mass and elemental analyses. The colour yield of the photografted cotton is seven times higher than that of conventional dyeing. Furthermore, good colour fastness properties are attributed to the water‐insoluble polymeric dyes formed.     

Dopant macroinitiator for electropolymerisation and functionalisation of conducting polymer thin films

Grafting of polymer brushes from conducting polymer (CP) thin films by controlled radical polymerisation provides a versatile route for the synthesis of functional, electroactive surfaces, with applications in diverse fields. However, one of the drawbacks of this approach is the difficulty of upscaling the synthesis due to the need for specialised CP precursor monomers functionalised with initiation sites. We herein describe an alternative approach to the synthesis of CP‐based polymer brushes whereby atom transfer radical polymerisation initiation sites are attached to a macrodopant incorporated into CP films during electropolymerisation. The facile electropolymerisation of commonly studied CPs with an initiator‐functionalised macrodopant – poly[(styrene sulfonate)‐co‐(2‐bromopropionyloxyethyl methacrylate)] – is demonstrated. The composite polymer films thus synthesised were used as substrates for grafting of hydrophilic polymer brushes. Although poly(styrene sulfonate) is commonly used as a macrodopant in CP films, its initiator‐functionalised derivatives have not previously been utilised in this manner. Despite the elegance of this approach, to the authors' knowledge, there have been no previous examples reported of utilising macromolecular dopants as initiators for subsequent grafting of polymer brushes. © 2017 Society of Chemical Industry     

Electroinitiated and radiation-induced polymerisation of epoxycyclopentane

Liquid state radiation-induced and electroinitiated polymerisations of epoxycyclopentane (ECP) have been investigated. Dichloromethane and tetrabutylammonium hexafluoro-phosphate were employed as a solvent electrolyte couple. Temperature effects on the rate of electroinitiation were also studied. Apparent activation energy for the electroinitiated polymerisation was calculated from the Arrhenius plot. The propagation of the polymerisation for both methods was found to be through the opening of the epoxy ring, as verified by i.r. and n.m.r. spectra. Both methods of polymerisation yielded tacky, amorphous polymers.     

Synthesis of styrene–isoprene A2B2 hetero-armed star copolymers

Styrene–isoprene A₂B₂ star copolymers having two arms of polystyrene and two of polyisoprene have been synthesised. Two routes have been followed. In the first, 2 moles of polydienyl lithium were coupled, without loss of carbanionic character, by reacting with 1 mole of 1,3-bis(1-phenylethenyl) benzene. The difunctional adduct was then used to initiate the polymerisation of styrene in the presence of a small amount of triethylamine which served to ensure a rapid crossover. In the second route, 2 moles of polystyrl lithium were coupled with 1 mol of SiCl₄ in benzene; no attendant formation of three-armed star was detected. Introduction of large excess of polyisoprenyl lithium, together with triethylamine as catalyst, generated the star which was isolated by fractional precipitation.