Electropolymerisation of methyl methacrylate on carbon fibre surfaces

The electroinitiated polymerisation of methyl methacrylate containing sulphuric acid was found to be localised at the surface of a cathode of carbon fibre. The influences of various reaction parameters on the rate of polymerisation and the molecular weight have been recorded but do not agree totally with classical free radical electropolymerisations. The behaviour of molecular weight and evidence of post-polymerisation suggest the existence of living polymer radicals. It is argued that atomic hydrogen is responsible for initiation of the polymerisation.     

Production of porous suspension polymers using a continuous tubular reactor

The conventional method for the synthesis of porous cross-linked copolymer beads is by suspension polymerisation. Suspension polymerisation reactions are generally performed in a stirred tank, which generally results in a large size distribution. By careful control of the polymerisation conditions, polymer beads can be produced using a tubular poly(tetrafluoroethylene) continuous reactor. Such beads are produced with the same average pore size, but with a lower degree of polydispersity than analogous systems produced in a batch reactor (stirred tank). This is achieved by density-matching the droplet and continuous phases (by the use of a brominated monomer or a porogenic diluent) and increasing the viscosity of the monomer phase (with the addition of small amounts of polystyrene). Received: 26 June 1999/Accepted in revised form: 7 October 1999     

Thiophosphoryl fluoride and phosphoryl fluoride as initiators for the polymerisation of tetrahydrofuran

Thiophosphoryl fluoride and phosphoryl fluoride have been found to initiate the polymerisation of tetrahydrofuran. The living polymer formed has a high molecular weight of the order of a million and the density is found to be between 0.98 - 1.02 g/cc. A cationic mechanism for the polymerisation has been proposed.     

Macrokinetics of the cationic copolymerization of isobutylene with isoprene

A theoretical model has been developed for the macrokinetics of cationic isobutylene–isoprene copolymerization in a stirred reactor and in a tubular turbulent reactor. The model provides means to calculate the reaction mass temperature, velocity, and turbulence kinetic energy fields. The adequacy of the model has been demonstrated using the Fisher criterion. Computational experiments have been carried out to estimate the effects of the catalyst concentration and the rotational speed of the stirrer (in the case of the synthesis conducted in a stirred reactor) and the effects of reaction mixture velocity and apparatus diameter (in the case of the synthesis conducted in a tubular turbulent reactor) on molecular weight characteristics of the resulting copolymer (butyl rubber).     

Mathematical Analysis of the Formation of Molecule Sizes on a Spinning Disc Reactor

A mathematical analysis of the behaviour of the molecular weights of addition polymers during a polymerisation process is described. Spinning disc reactor (SDR) technology has been shown to yield significant improvements in terms of polymerisation rates whilst retaining close control of the molecular weights and the molecular weight distributions^[1,2]. However, understanding of the kinetics of the polymerisation process on a SDR remains unresolved. One of the questions to be addressed concerns the sizes of the macromolecules preferably formed during the polymerisation process. To address this question, a mathematical analysis of the observed trends in number and weight average molecular weight, monomer concentration and polydispersity during the polymerisation process on a SDR has been undertaken. To validate the results, experimental data obtained from benzoyl peroxide initiated free radical polymerisation of styrene on a SDR^[2] was used. It was concluded that most of the monomers consumed are in the growth of smaller size chains.     

Production of porous suspension polymer beads with a narrow size distribution using a cross-flow membrane and a continuous tubular reactor

The work described focuses on a two-stage process for the production of large porous suspension polymer beads of defined particle size and narrow size distribution. Emulsification has been performed using purpose built cross-flow membrane equipment, which allows controlled production of large emulsion droplets with a much narrower size distribution. The work described compares the production of large emulsion droplets of monomer prepared both by agitation and using a cross-flow membrane. The effects of variations in the pore size of the membrane and flow-rates on the size of the emulsion droplets produced are also investigated. The second stage of the process is polymerisation of performed monomer emulsion droplets using a continuous tubular reactor. Samples polymerised using such a method show a narrower size distribution than similar systems polymerised as a batch.     

Effect of the nature of the alkyl group on initiation and termination in R3Al/RLi initiation of methyl methacrylate

The polymerisation of methyl methacrylate has been investigated with mixed aluminium and lithium alkyls. The use of sterically hindered aluminium alkyls such as triisobutyl aluminium in conjunction with tert-butyl lithium leads to living polymerisation at 0°C with little complications from secondary initiation or premature termination. The use of less bulky alkyl groups on either aluminium or lithium leads to both secondary initiation, as observed by the formation of high molecular weight polymer by GPC-LALLS and termination via cyclisation as observed by MALDI-TOF-MS. The initiator efficiencies, even when living polymerisation ensues, are considerably less than 100%.     

Characterization of Ethylene Copolymers with Liquid Chromatography and Melt Rheology Methods

Summary: Melt rheology and polymer chromatography methods were applied to characterize molecular heterogeneities in products of free radical copolymerization of ethylene with methyl acrylate and vinyl acetate comonomers performed in continuously stirred tank and tubular reactors. We found that the ethylene–vinyl acetate copolymers made in both reactors had similar linear viscoelastic properties typical to branched products of the high pressure process. But the ethylene–methyl acrylate copolymers obtained in the tubular reactor had unusually high melt viscosity at low shear rate and much lower onset of shear thinning despite the narrower molecular weight distribution and the lower overall amount of long-chain branches compare to their autoclave counterparts with similar average molecular weight and chemical composition. Using interaction polymer chromatography method called gradient elution at critical point of adsorption we found that ethylene-acrylate copolymers from the tubular reactor had very broad chemical composition distribution, which was consistent with a significant difference in reactivity ratios between ethylene and acrylate comonomers. Such chemical composition heterogeneity can be a reason for the observed unusual rheological properties of these copolymers.     

Chemical and thermo‐responsive characterisation of surfaces formed by plasma polymerisation of N‐isopropyl acrylamide

Plasma polymerisation of N ‐isopropyl acrylamide (NIPAAm) presents an exciting route for the production of thermally responsive coatings on a wide variety of substrates for applications in tissue culture and microfluidics. One issue associated with the polymerisation of NIPAAm via plasma polymerisation is the limited volatility of the monomer and the subsequent requirement for monomer and reactor heating to create and maintain the vapour. It is already well established that power is critical in the balance between polymer functionality and coating stability in plasma polymers. However, little is known of how reactor and substrate temperatures may be used to influence the physico‐chemical characteristics of polymers produced from such low‐volatility monomers. In this paper, we examine the effects of a range of plasma deposition parameters on the functionality and stability of plasma‐polymerised NIPAAm surfaces. X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure spectroscopy (NEXAFS), ellipsometry and contact angle goniometry have been used to examine coating chemistry, stability in aqueous environments, deposition rates and thermo‐responsive behaviour. Our results indicate that plasma polymerisation at low powers and low temperatures enhances the ability of plasma‐polymerised NIPAAm to display a wettability phase transition, but also contributes to instability of the coating to dissolution or delamination in water. Our spectroscopic measurements confirm that retention of the monomer structure is facilitated by low power and temperature deposition and reveal that conversion of the amide groups to amine and nitrile groups occurs during the polymerisation process, particularly at high discharge powers. Copyright © 2006 John Wiley & Sons, Ltd.     

In-Situ Monitoring of Emulsion Polymerisations of MMA and Styrene Using Conductimetry and Calorimetry

In the present work, conductimetry is applied for on-line evaluation of anionic surfactant dynamics during emulsion polymerisation of methyl methacrylate and styrene and for on-line estimation of particle size and number. Reactor and jacket temperatures are used to perform energy balance computations on-line and to provide on-line evaluation of monomer conversion. The parameters of a previously proposed model are re-estimated in order to describe the conductivity signal during methyl methacrylate runs. Some important issues regarding the effects of the surfactant micelles over the conductivity signal are addressed. Finally, the model is inverted and combined with conversion and reactor temperature measurements, providing good predictions of the number of polymer particles in the latex, without needing of on-line measurements of particle size.     

Effects of Monomer Flow Rate,Flow Configuration,and Reactor Geometry on the Rate of Plasma Polymerization

The effects of flow rate on the plasma polymerization of ethylene in an rf discharge were investigated using both a tubular and a bell-jar-type of reactor. Both reactors contained parallel plate internal electrodes. Experiments with the tubular reactor showed that both the total thickness of the deposit and its distribution in the axial direction were strong functions of the flow rate. At low flow rates the polymer thickness decreased in the flow direction, while at high flow rates the polymer thickness increased. Each of these observations is explained by a simple model of plasma polymerization. Using the bell-jar reactor, different monomer flow distribution configurations were tested to determine their effect on the distribution of polymer thickness. It was found that distribution or diffusion of the monomer inflow provided a more uniform film.     

Effect of macro-RAFT agent on the morphology of polymer dispersed liquid crystals

In this study, macro-(RAFT) reversible additional fragmental chain transfer agent prepared by reversible additional fragmental chain transfer polymerisation has been incorporated into polymer dispersed liquid crystals (PDLCs). The effects of concentration, molecular weight and glass transition temperature of macro-RAFT agent were studied in terms of morphology, polymerisation kinetics, molecular weight of polymer matrix and electro-optical properties of the films. It was found that the key factor influencing morphology was the mobility of macro-RAFT agent chain rather than polymerisation rate and molecular weight of polymer matrix. Furthermore, the decrease in the mobility of macro-RAFT agent chain caused less liquid crystal nematic fraction, smaller liquid crystal domain size and greater driving voltage.     

Development of an Unsteady-State Model for Control of Polymer Grade Transitions in Ziegler-Natta Catalyzed Reactor Systems

The dynamics of the activity and polymer growth in Ziegler-Natta catalysts has been well established in the literature. 1 , 2 The corresponding dynamic behaviour of the reactor system is predicted using a segregation model approach and the unsteady state model of residence time distribution previously developed. 3 The model is therefore able to predict reactor performance for a time-varying catalyst flow rate through the reactor, as well as time-varying concentrations of monomer, co-catalyst and chain termination agent. A method of determining grade transition policies by the use of the developed reactor models is then presented. It is demonstrated that the reactor productivity, catalyst efficiency, average chain length and polydispersity can be controlled by the catalyst flow rate and reactor monomer and hydrogen concentrations. The relationship between the required polymer product properties and the system flow rates is determined. Case studies are presented that evaluate various transition strategies for a specific polymer grades.     

First report of reversible addition-fragmentation chain transfer (RAFT) polymerisation in room temperature ionic liquids

The Reversible Addition-Fragmentation chain Transfer (RAFT) polymerisation of acrylates, methacrylates and styrene is reported for the first time in room temperature ionic liquids; the acrylate and methacrylate polymerisations show a living character and lead to well-characterised polymers, with narrow polydispersity (< 1.3); in the case of styrene, the insolubility of the polymer in the ionic liquids stops the polymerisation at an early stage.     

Simulation of Polymer Reactors Using the Compartment Modeling Approach

A compartment modeling approach based on computational fluid dynamics (CFD) simulations is applied to a simplified static mixer geometry. Compartments are derived from velocity fields obtained from cold CFD simulations. This methodology is based on the definition of periodic flow zones (PFZ) derived from the recurrent flow profile within the static mixer. In general, PFZ can be characterized by two different compartments: flow zones with hydrodynamic behavior of a tubular reactor and dead zones exhibiting a more continuous stirred tank reactor‐like characteristic. In CFD studies the influence of changing fluid properties, for example viscosity, on flow profile due to polymerization progress is considered. In the deterministic compartment model, the continuous flow profile within the static mixer is transformed to basic reactor models interconnected via an exchange stream. To reduce model complexity and the number of model parameters, constant volumes of compartments are assumed. Changes in hydrodynamics are considered by a variable exchange flow rate as a function of Re manipulating residence time in compartments. Simulation studies show the influence of decreasing exchange flow rates with polymerization progress, as Re decreases, resulting in a greater increase of viscosity in dead zones. The reactor performance is qualitatively represented by the simulation results.     

Kinetic Study of the Copolymerisation of Ethylene with a Single Site Catalyst in Propane Slurry Polymerisation

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1-hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5-litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1-hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1-hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.     

Double UV polymerisation with variable temperature-controllable selective reflection of polymer-stabilised liquid crystal (PSLC) composites

In this study, a method of preparing wide-band reflection cholesteric liquid crystals (CLCs) films by UV-radical polymerisation in combination with UV-cationic polymerisation is proposed. Because the helical twisting power (HTP) of the chiral dopant decreases with increasing temperature and the polymerisation rate of UV-initiated free radical polymerisation is faster than UV-initiated cationic polymerisation, by adjusting the temperature, broadband reflective films with non-uniform pitch distribution are obtained. The fractured surface of the polymer network of the broadband reflective films is observed by scanning electron microscopy (SEM), which reveals the presence of non-uniform pitch distribution. In addition, the influences of monomer concentration, UV light intensity and UV curing time on the consequent non-uniform pitch distribution have been studied.     

Polymerisation in lyotropic liquid-crystalline phases of dioctadecyldimethylammonium bromide

The polymerisation of styrene in lyotropic liquid-crystalline (LC) phases of dioctadecyldimethylammonium bromide (DODAB) in water is explored. Amphiphile concentrations between 20 and 50 wt % are employed. The study is set out as a model study for polymerisation reactions in nonstabilised, nonfunctional bilayer systems. X-ray characterisation was used to assess the phase behaviour of the lyotropic mesophases before, during and after polymerisation. The DODAB/water system forms the lamellar phase within the concentration range considered. Addition of styrene to the lamellar phase of DODAB at an equimolar ratio induces a phase shift to a bicontinuous cubic phase at elevated temperatures near the phase-transition temperature. Upon polymerisation within this cubic phase, the phase structure is maintained if the system is kept at constant temperature; however, if the polymer/amphiphile phase is cooled, the lamellar phase, being typical of the DODAB/water system, is restored. It is concluded that, as a result of phase separation between the polymer and the amphiphile phase, the polymerisation in lyotropic LC phases does not provide a stable copy of the templating amphiphile phase. This is in analogy to the observations for polymerisations in other lyotropic phases. Received: 16 March 2000 Accepted: 1 July 2000     

Anionic polymerisation of caprolactam at the small-scale via DSC investigations

This work was part of a major project aiming to produce polyamide 6 parts using an additive manufacturing process. This is by manufacturing 3D parts layer by layer. The influence of heating strategy (heating rate, cooling rate and maximum temperature) on anionic polymerisation of caprolactam in a small-scale was investigated by means of differential scanning calorimetry (DSC). The relationship between heating rate and the polymerisation–crystallisation processes was determined. Two different catalyst/activator compositions were used to study the influence of a di-functional activator on polymerisation. Results showed that unlike cooling rate, the heating rate and maximum heating temperature had a major effect on the final properties of polymer such as crystallinity, monomer conversion and polymer chains regularity. Using a di-functional activator resulted in slowing down the crystallisation process due to the enhanced rate of branching.     

Electrochemical polymerisation of 2-aminofluorene in ethylalcohol/water medium

Electrochemical polymerisation of 2-aminofluorene, 2AF, was investigated in ethylalcohol/water mixture (3:2, v:v) in the presence of HClO₄ as the supporting electrolyte via constant potential electrolysis, CPE. Prior to CPE, electrochemical behaviour of the monomer was investigated in the same solvent-electrolyte couple utilising cyclic voltammetry, CV. Electrochemical polymerisation of the monomer yielded insoluble, dark bluish-green, conducting polymer deposit on the electrode surface. Characterisation of the polymer film has been carried out using FT-IR spectroscopic technique and thermal behaviour was studied using differential scanning calorimetry, DSC. Spectroelectrochemical, SPEL, behaviour of the polymer on ITO working electrode was studied by recording the electronic absorption spectra, in situ, in monomer-free solution at different potentials and it is found that the film can be reversibly cycled between −0.1 and 1.1 V vs SCE. Paramagnetic behaviour of the polymer was monitored using in situ ESR spectroscopy. The temperature dependence of conductivity supported the Mott's variable range hopping, VRH, mechanism for poly(aminofluorene), PAF.