Effects of Ultrasonic Vibration on the Electroinitiated Copolymerisation of Styrene and Isoprene

Copolymerisation of styrene and isoprene by constant potential electrolysis in dichloromethane was achieved at different polymerisation potentials. Effect of ultrasonic vibration on the rate and the yield of polymerisation has been discussed. The composition of the copolymers was found to be affected by the vibration as well as the polymerisation potential (E_pol). At E_pol=+3.30 V we found that r₁=r₂ and mole percents of isoprene and styrene in copolymer were equal to each other. Equality was also observed on reacted monomer concentrations, at that potential, which can be called critical polymerisation potential. At E_pol values above or below the critical polymerisation potential none of the above-mentioned properties were equal. Monomer reactivity ratios were determined by the integrated Lewis-Mayo equation. Ultrasonic vibration as well as polymerisation potential was found to affect reactivity ratios.     

Gel-gel reaction in RAf and RA2+RBf polymerisations

Summary The amount of gel-gel reaction in RA_f and RA₂+RB_f random polymerisations is evaluated. For a given functionality f and stoichmetric amounts of reactants, half as much gel-gel reaction occurs in RA₂+RB_f polymerisations by complete reaction as in RA_f polymerisations. This difference is readily understandable in that the formation of a loop requirestwice as many pairs of groups to react in the former type of polymerisation as in the latter. Gel-gel reaction is necessary for the formation of the network structure at complete reaction. However, it also leads to network imperfections, viz. inelastic loops.Dedicated to Prof. Walther Burchard on the occasion of his 60th birthday     

Isolierung und Charakterisierung von niedermolekularem Polyvinylchlorid

Using suitable conditions of polymerisation low molecular weight PVC was prepared in CCl₄ in the presence of isobutylen. The rate of thermal degradation increased as the molecular weight of the fraction decreased. The heat stability was less when dicyclohexylperoxodicarbonate was used instead of azoisobutyronitrile as an initiator. The substances with the lowest molecular weight were obtained as a colorless liquid by destillation of the polymerisation solvent at 90°C–110°C (10^?4 Torr). The analysis of the products revealed the presence of structures which were not identical with those of PVC-homologues with low degree of polymerisation, but combination products of CCl₄ and isobutylen.     

Polymerisation of bicyclohepta-(2,5)-diene with palladium-π-complexes

A pinene-π-allylic complex of palladium was capable of catalysing the polymerisation of bicyclohepta-(2,5)-diene. Polymerisation pattern was the same as in the case of PdCl₂, i.e. only one double bond of the diene was opened by this reaction. The optimum temperature range for the polymerisation was between 130 and 200 °C. Polar solvents retarded the reaction. The Pd-π-allylic complex, for the polymerisation of the same olefin, was a more active catalyst than other palladium compounds (e.g. PdCl₂).     

Sodium metabisulphite initiated aqueous polymerisation of methyl methacrylate

Sodium metabisulphite (Na₂S₂O₅) has been found to initiate the aqueous polymerisation of methyl methacrylate (MMA) at 35°C in phosphate buffer solutions of pH 6.85 and a constant ionic strength (μ) of the media in an inert atmosphere of pure nitrogen. The reaction has a well defined induction period which is a function of the concentrations of the initiator, of the monomer and also of temperature. The polymerisation is signalled by the sudden appearance of a haze at the end of the induction period in a given run, and the polymer separates out as a coarse precipitate during the progress of the polymerisation reactions. When the conversion is over 50 per cent complete, the polymerisation media looks like a thick curd if the monomer concentration is relatively high. The rate of polymerisation is found to decrease with conversion or time in a given run, and the initial rate (v_p), obtained by extrapolating the linear yield/time versus time curves to zero time, keeping the conversion below 10 percent, is found as where (I) = initiator concentration in the range, (0.26 to 3.94) × 10^?3 (mol dm^?3), and (M) = monomer concentration in the range 0.019 to 0.141 (mol dm^?3). At high initiator concentrations, the rate of polymerisation is found to decrease. In a given run, the viscosity average molecular weights (M _v) of the polymers is found to increase quickly with a conversion of up to 25 to 30 percent, and then slowly with the further increase in conversion. (M_v) however is found to decrease with the increase of the initiator concentrations at a given conversion but increases with the increase of the monomer concentrations. Hydroquinone inhibits the polymerisation reactions, whereas air is found to increase the induction period, but later enhances the polymerisation rate in the same run. It has been shown that the bisulphite addition reaction of MMA is not important under the experimental conditions, and the polymerisation occurs by the free radical mechanism. The rate constant (k₂) of the reaction, has been estimated from the analytical data as, k₂ = 14.62 × 10^?2 (dm³ mol^?1 s^?1) at 35°C.     

Molybdenum-doped epoxy resins as catalysts for the epoxidation of alkenes

Epoxy resins were polymerised using molybdenum ethoxide and 2-ethylhexanoate as polymerisation initiators. The thermosets thus obtained are useful epoxidation catalysts for a variety of alkenes, including propene with tert-butyl hydroperoxide as an oxidant. To investigate the long-term performance of these resins, they were used repeatedly in up to 120 reactions without any reconditioning. Compared with other catalyst systems based on organic polymers, they reveal unprecedented long-term activities over periods of months so that catalyst lifetimes of years can be expected. Di-, tri-, tetra- and oligofunctional epoxy resin monomers were used and compared. The catalytic performance of the thermosets strongly depends on the resin type and the polymerisation initiator. Promising results were obtained with monomers bearing 3 or 4 glycidyl groups in combination with Mo(OEt)₅ as an initiator. Metal leaching, determined by sensitive atomic spectroscopic techniques, is extremely low. Inorganic–organic hybrid catalysts can be easily prepared by adding inorganic components such as silicagel to the liquid resins, followed by polymerisation.     

The ROMP catalysts Mo(CO)5PPh3/alkylaluminum with unstrained cyclic and linear dienes as initiators of the addition polymerisation

Summary We study the polymerisation of a series of unstrained cyclic and acyclic dienes with the catalytic system of Mo(CO)₅PPh₃/alkylaluminum. The Mo(CO)₅PPh₃/alkylaluminum catalyse the nonmetathesis polymerisation, through a pair of ionic complexes similar to that of Ziegler-Natta mechanism, and not through the ROMP (Ring-Opening-Metathesis-Polymerisation) mechanism followed by strained olefins. Because of the nature of these complexes the reactivity is lower with respect to that of a common Ziegler-Natta catalyst, such as Cp₂TiCl₂/Et₃Al₂Cl₃, as it is demonstrated, by means of kinetics and ESR measurements, in the case of the polymerisation of of 1,5-cyclooctadiene. Similarly to the Ziegler-Natta catalysts, they give cyclised products in the polymerisation of 1,5-hexadiene and 1,7-octadiene, and the 1,4-cis unit in the case of the polypentadienes. Finally we find that they are active catalysts for the polymerisation of styrene. Received: 12 March 1998/Revised version: 20 April 1998/Accepted: 22 April 1998     

A simple model of hyperbranched polymerisation involving AB<Subscript>2</Subscript> and B<Subscript><Emphasis Type="Italic">f</Emphasis></Subscript> core monomers and methods of narrowing the molecular size distribution

Summary A simple kinetic model of modelling hyperbranched polymerisation involving AB₂ and B_f core monomers is developed and analytical solutions of the model are presented. The number- and weight- average polymerisation degrees can be calculated using the model as functions of polymerisation time or conversion degree. Application of the model is tested for predicting the broadness of molecular size distribution of the hyperbranched polymers obtained by varying the procedures of feeding AB₂ monomer to polymerisation reactor.     

Effects of phosphorous oxychloride,phosphorous trichloride and dichlorophenylphosphine on the radical polymerisation of acrylonitrile under heterogeneous conditions

Summary The effects of C₆H₅PCl₂, POCl₃, and PCl₃ on the free radical polymerisation of acrylonitrile initiated bya,a-azobisisobutyronitrile were kinetically investigated in benzene and trichloroethylene solutions. With PCl₃ rates of polymerisation were unaffected but the degrees of polymerisation were found to decrease with increasing PCl₃. With C₆H₅PCl₂ and POCl₃ however both rates and degrees of polymerisation were adversely affected. Thus PCl₃ acts as a chain transfer agent while the other two phosphorous compounds function as degradative chain transfer agents.     

Determination of initiator decomposition constant in a heterogeneous polymerisation system

A new method for determination of initiator decomposition constant k_d is described based on the use of instantaneous polymerisation rates for two similar experiments run with different initiator concentrations. The constant found will be specific for the polymerisation system used. If the propagation and termination rate constants for the monomer are known from other studies the initiator efficiency factor f can then be obtained. To verify the validity of the method, poly(vinyl chloride) latexes were prepared by potassium persulphate (K₂S₂O₈) initiated polymerisation of submicron-sized monomer droplets. The monomer droplets were obtained by diffusion of vinyl chloride monomer into a preformed emulsion of water-insoluble oil droplets. The polymerisation was performed in an isothermal calorimeter. From the measured heat evolution, the instantaneous polymerisation rates were calculated. The thermal decomposition constant of potassium persulphate k_d was determined to be 2·5×10^-6s^-1 at 51°C. In the same system the order of reaction with respect to the initiator concentration was found to be 0·50. © 1998 SCI.     

Experimental study of vapor permeation of C5C7 alkane through PDMS membrane

Vapor permeation through dense membrane is regarded as an effectively way to separate volatile organic compounds (VOC) from industrial gas stream. This study proposes a new method to get the solubility and diffusivity of pure VOC vapor in dense membrane. C₅H₁₂, C₆H₁₄ and C₇H₁₆ were selected as sample VOC components to conduct newly developed sorption experiment with polydimethylsiloxane (PDMS) membrane. For each considered VOC component, its solubility was obtained from measured sorption equilibrium concentration in PDMS membrane, and its diffusivity was determined by fitting diffusion equation to the measured transient concentration of VOC component. The permeation behavior of VOCs in PDMS membrane was analyzed in terms of their solubility, diffusivity and permeability. Furthermore, the obtained solubility of these VOC components was utilized to get the vapor–membrane interaction parameters in UNIQUAC model. This opens an effective way to obtain the activity coefficient of VOC components for predicting their permeation performance in PDMS membrane.     

Effects of poly(vinyl acetate) suspending agents on suspension polymerisation of vinyl chloride monomer

Abstract

When partially hydrolysed poly(vinyl acetate) (PVAc) is used as a suspending agent in the suspension polymerisation of vinyl chloride monomer, it has significant effects on the morphology of the resulting poly(vinyl chloride) (PVC) particles. At the initial step of polymerisation, PVC molecules are grafted onto the molecules of the suspending agent forming a PVC–PVAc membrane. The properties of this membrane depend on the type of suspending agent, the polymerisation temperature, the mixing efficiency, and other factors. The morphology of the growing PVC particles and the properties of the PVC resin obtained depend in turn on the characteristics of the membrane. A model has been developed relating to the connection between the polymerisation conditions and the characteristics of the suspending agent on one hand, and on the PVC properties on the other hand. The model is based on an analysis of the characteristics of the PVC–PVAc membrane and their effect on PVC properties.     

Calculation of heat of polymerisation: group-contribution method

Heat of Polymerisation of a polymeric system is largely dependent on its monomer. So depending upon the structure of the monomer, the prediction of the heat of polymerisation can be done. In the present study the structural features of the monomer, that is undergoing polymerisation reaction, has been assumed to be responsible for the heat of polymerisation. To calculate the heat of polymerisation of a particular reaction, Group-Contribution method (GC-method) has been used. Certain values (S_R value) have been assigned for the different structural units, present in the monomers. The S_R values have been obtained by correlating of the heat of polymerisation of a large number of polymers. Addition of the S_R values corresponding to the structural units of the monomer will give the heat of polymerisation of that particular reaction. This GC-method is applicable where liquid monomers form condensed polymers. This empirical method gives quite satisfactory results in calculating the heat of polymerisation for a large number of polymeric systems. Received: 23 October 1998/Revised version: 9 December 1998/Accepted: 15 December 1998     

Redox polymerisation—kinetics of polymerisation of acrylamide initiated by the Mn3+-citric acid redox system

The kinetics and mechanism of polymerisation of acrylamide initiated by manganese(III) acetate-citric acid (CA) redox system in aqueous acetic acid and sulphuric acid medium were studied over the temperature range 30-50° C. The overall rates of polymerisation (R_p), disappearance of manganic ion (—R_m), and degree of polymerisation (X?_n) were measured with variation in [monomer], [Mn³⁺], [CA], [H⁺], μ and temperature. The polymerisation is initiated by the organic free radical arising from the Mn³⁺-CA reaction and the termination is by metal ions. The various rate parameters were evaluated and discussed.     

Directional polymerisation and electronic properties of a cyanosubstituted dialkylpolyphenylenevinylene

Summary The synthesis of a monomer allowing for directional polymerisation based on the Knoevenagel condensation reaction is presented. The free running polymerisation gave a molecular weight (M _w = 24650 g mol^-1) polymer product. The polymerisation reaction could be followed by size exclusion chromatography (SEC) and the molecular weight of the polymer product could be controlled by termination of the polymerisation reaction at a suitable time. When terminated before completion a lower molecular weight product was obtained that could be separated into oligomers using preparative SEC. The polymer product and the oligomers were found to have very similar physical properties in terms of the optical band gaps, electronic energy levels and charge carrier mobilities as studied by UV-vis and pulse radiolysis time resolved microwave conductivity (PR-TRMC). Finally the positions of the filled energy levels were determined using ultraviolet photoelectron spectroscopy (UPS).This revised version was published online in September 2004. Due to technical problems, the previous version contained an incomplete PDF.     

Studies of the reactions of anhydrosulphites of α-hydroxy acids,part IX. thermal polymerisation of anhydrosulphites of α-hydroxy α-methyl carboxylic acids

The anhydrosulphites of a series of unsymmetrically substituted α-hydroxy acids have been prepared and their susceptibility to polymerisation by thermal decomposition studied. The first order rate determining ring scission process, leading to the formation of a reactive α-lactone intermediate which then undergoes spontaneous polymerisation, is the predominant mechanism even with substituents up to C₈. As the length of the n-alkyl substituent is increased the rate of decomposition and thus polymerisation increases until a plateau value is reached at around C₃. Further increase in substituent length decreases the rate of decomposition, an effect which is attributed to steric hindrance of the leaving group by long (C₆—C₈) substituents.     

Studies on the photopolymerisation of vinyl monomers using amine-organic halide systems as initiators

Amine-organic halide systems have been found to be good photo-initiators for the polymerisation of vinyl monomers in a benzene medium. The n-tertiary butylamine-carbonte-trachloride (TBA-CC1₄) system is most suitable for the polymerisation of methyl meth-acrylate (MMA) in the presence of light. The rate of polymerisation (Rp) and degree of polymerisation (P̄n) are found to be independent of incident light intensity (Io). Rp and 1/P̄n are linearly related to [TBA]^0.5 up to [TBA] = 0.108M, but above this concentration, TBA acts predominantly as a retarder. Rp and 1/P̄n are proportional to [CC1₄]^0.5 at low [CC1₄]. At [CC1₄] > 0.099M it acts predominantly as a transfer agent. Furthermore, Rp is always proportional to [MMA]^1.0 Endgroup analysis by dye-partition test shows that both amine bearing radicals and CC1₃ radicals are the initiating species and an average of about one total endgroup per polymer molecule up to [CC1₄] = 0.099M indicates bimolecular termination of the poly (MMA) radicals through disproportionation. Higher chlorine endgroup and total endgroup incorporation at [CC1₄] > 0.099M gives additional evidence of the preponderance of chain transfer under this condition. A suitable mechanism of polymerisation is suggested, based on kinetics and endgroup evidence.     

Functionalised multi‐walled carbon nanotubes for epoxy nanocomposites with improved performance

BACKGROUND: Carbon nanotubes (CNTs) are fast becoming key components in the production of high‐strength composite materials. Two methods to prepare nanocomposites by covalent bonding between an epoxy matrix and functionalised CNTs that acted as cross‐linkers during polymerisation were investigated. RESULTS: In the standard method, 1 wt% functionalised CNTs was dispersed in epoxy, hardener was added and the composite was cured. In the masterbatch approach, 1 wt% functionalised CNTs was mixed with epoxy in the presence of triethylamine accelerator, then cured. This yielded partially cured epoxy; additional hardener was required to achieve complete curing. Improvements were observed in storage modulus (E′), flexural modulus (E_B), wear resistance and hardness. Thermal stability did not change appreciably for samples prepared by either the standard or masterbatch methods. Variations in the results obtained as a function of preparation method, functionalised CNTs and hardener used are discussed. CONCLUSION: Epoxy nanocomposites having improved mechanical properties were obtained by incorporating functionalised CNTs. Better interaction between the epoxy and CNT was achieved using the masterbatch method; this was attributed to covalent bonding between the CNTs and epoxy. However, optimisation of the CNTs, accelerator and hardener used in composite preparation is required to obtain improved physical properties. Copyright © 2009 Society of Chemical Industry     

Effect of synthesis parameters on the electrical conductivity of polypyrrole‐coated poly(ethylene terephthalate) fabrics

The effects of pyrrole, anthraquinone‐2‐sulphonic acid (AQSA) and iron(III) chloride (FeCl₃) concentrations, reaction time and temperature on the electrical conductivity of polypyrrole (PPy)—coated poly(ethylene terephthalate) (PET) fabrics were investigated. With an increase in both the AQSA and FeCl₃ concentrations, resistivity decreased to a point beyond which higher concentrations led to increased surface resistivity. Erosion of the polymer coating, in dynamic synthesis from continual abrasion, manifested as an exponential increase in the resistance of the coated textile substrate. This was not encountered in static synthesis conditions. Temperature affected the degree of surface and bulk polymerisation. The effect of polymerisation temperature on conductivity was negligible. Conductive polymer coating on textiles through chemical polymerisation enabled a smooth coherent film to encase individual fibres, which did not affect the tactile properties of the host substrate. The optimum FeCl₃/pyrrole and AQSA FeCl₃/pyrrole molar ratios were found to be 2.22 and 0.40 respectively. Copyright © 2003 Society of Chemical Industry