Showing papers by "Imperial Chemical Industries published in 2007"

Some factors affecting the solubility of polymers

Abstract: The solubility of a polymer in a non-polymeric liquid depends mainly on the heat of mixing. When no polar forces are concerned, the cohesive energy densities of polymer and solvent must be close; a method is given for estimating the cohesive energy densities of polymers from a set of additive constants, and it is shown that good agreement is found between values so calculated and values obtained by swelling measurements. The effects of dipole interactions and hydrogen bonding are also discussed. The solubility of polyvinyl chloride in a number of solvents is considered, and correlated with both the cohesive energy density of the solvent and its ability to form hydrogen bonds.

Biotechnology. An industrial view

Abstract: Biotechnological research has witnessed enormous progress, particularly in the last decade The popular concept of biotechnology is that it is concerned with the production of new wonder drugs, such as interferon However, another side to the subject is large-scale biotechnology concerned with the biological processes for making many of the everyday bulk production on which society depends An industrial view of biotechnology is given with examples such as ammonia production, penicillin, single-cell protein, methanol and polyhydroxybutyrate

Gas chromatography. I. The separation and estimation of volatile organic compounds by gas-liquid partition chromatography

Abstract: An extension of the work of James and Martin on the separation of volatile fatty acids and bases by gas—liquid partition chromatography is described. This technique has now been applied to the analysis of most types of volatile organic compounds on a milligram scale; mixtures of hydrocarbons, alcohols, ethers, esters, aldehydes and ketones have been separated on a column of kieselguhr impregnated with di-(3: 5: 5-trimethylhexyl) phthalate, and the components determined by a thermal-conductivity method.

The use of Caenorhabditis elegans for anthelmintic screening

Abstract: Caenorhabditis elegans maintained on ampicillin-treated Escherichia coli has been found to be sensitive to the benzimidazole anthelmintics, albendazole, cambendazole, fenbendazole, flubendazole, mebendazole, oxfendazole, oxibendazole, parbendazole, thiabendazole and the non-benzimidazoles, avermectin B1a, bitoscanate, febantel, levamisole, morantel, nitroscanate, oxantel, phenothiazine, pyrantel, pyrvinium pamoate, rafoxanide and stilbazium iodide at concentrations of 50 μg cm−3 or less. It can therefore be used in a high through-put in vitro pre-screen for anthelmintics. It is suggested that C. elegans may also be useful for evaluating the mode of action of drugs and the mechanism of resistance of nematodes to anthelmintics.

Crystallization phenomena in fibre-forming polymers†

Abstract: The present position reached in a general study of how fabrication conditions affect the crystalline texture and therefore the properties of crystalline polymers is reviewed. The mechanism by which long-chain molecules order themselves into some form of crystalline array is postulated to be one involving normal nucleation processes, but modified to take account of the fact that polymers melt over a range of temperatures, and the nucleation act is followed by preferential crystal growth in the direction of the polymer chains. This mechanism, with the additional concept of coiling growth, is not inconsistent with kinetics that fit the crystallization-rate processes on the one hand and observable structure in crystalline polymers on the other. It is considered that lateral accretion of the polymer molecules to the already formed long helical polymer-crystal results in haphazard branching growth with the new fibril developing along a path parallel to the parent crystal. This leads to the formation of coiled families of fibrillar crystals and this structure appears to be a suitable model on which to explain the many wide-angle and low-angle X-ray observations that have been made at various stages of the drawing and relaxing of filaments of crystalline polymers.

The oxidation potentials of phenolic and amino antioxidants

Abstract: A simple and rapid polarographic method of measuring the relative oxidation potentials of organic compounds has been developed, and values for a large number of phenolic and amino compounds have been determined to find whether any relationship exists between oxidation potential and antioxidant activity. Buffered electrolytes at various pH levels were used and when the determined potentials are plotted against the pH of the electrolyte, most monohydric phenols give straight-line graphs which correspond closely to the theoretical equation for oxidations in which hydrogen ions are involved in the electrode process E = E0 – 0·058 pH at 20° where E0 is the standard oxidation potential. Other phenolic compounds give graphs showing a ‘break point’ at about pH 6, and have different slopes above and below this value. Most of the hydroxyanisoles and amines exhibit slight curves when potential is plotted against pH. Sufficient alkylated phenols have been examined to establish definite trends in the effects of substitution; thus ortho and para substituents lower the oxidation potential by about 0·08 v while meta substituents have a much smaller effect. These effects are largely additive and the oxidation potentials of polyalkylated phenols can be predicted from a knowledge of the effects of the separate substitutents. With certain 2: 4: 6-compounds containing large groups, the measured oxidation potential is higher than that predicted and this is attributed to steric hindrance. In general, as the oxidation potential decreases, the antioxidant activity increases. The relationship is not invariably close and, with certain substituted hydroxyanisoles, the antioxidant activities measured are even higher than would be anticipated from their low potentials. No compound of high antioxidant activity has been found to possess a potential higher than 0·70 v and hence the polarographic method should prove to be valuable for a rapid preliminary assessment of possible anti-oxidants.

Quantitative analysis in the 2-μ, region applied to synthetic polymers†

Abstract: The application of short-wave (below 2μ) spectroscopy in the examination and analysis of synthetic polymers is described with special reference to molecular weight determination by end-group estimation, determination of monomer in polymers, and analysis of copolymers.

The solvent action of organic substances on polyacrylonitrile

Abstract: The facts concerning the solvent action of organic substances on polyacrylonitrile have been collected from diverse sources and new observations have been made. A new relationship between the boiling points of organic compounds and their latent heats of evaporation has been devised which is more accurate than the Hildebrand function, and this, together with new calculations and measurements of latent heats of evaporation, has been used to elucidate the relationship between the cohesive energy densities (C.E.D.) of organic compounds and their solvent power for polyacrylonitrile. All solvents for polyacrylonitrile are highly polar in character. Most of the best solvents have very high C.E.D.s in the neighbourhood of 220 to 230 cal./c.c. A separate calculation shows that this is approximately the C.E.D. of the polymer. It is believed that the molecules of such solvents have no greater attraction for the polymer molecules than they have for their own kind, solution being brought about by the increase in entropy. N-Disubstituted amides, and probably cyclic sulphones possess strong solvent action at lower C.E.D.s (116–170 cal./c.c.), and this is probably because the molecules of these substances have a slightly greater attraction for the polymer molecules than they have for their own kind. Most strongly hydrogen-bonded substances, such as alcohols, phenols, carboxylic acids, unsubstituted amides, and monosubstituted open-chain amides are non-solvents at all levels of C.E.D. The powerful attraction of the molecules of such substances for each other is not matched by an equally powerful attraction for the polymer molecules, and solution cannot therefore take place. In some cases these hydrogen-bonded substances make a strong contribution to the solvent power of mixtures. If the C.E.D. of the polyacrylonitrile is reduced by interpolymerization with a polymerizable hydrocarbon, solvents such as open-chain esters, ketones, and mono-reactive nitriles possessing lower C.E.D.s will attack it. This shows that ketones, open-chain esters, and mono-reactive nitriles fail to dissolve polyacrylonitrile because none of these substances possesses the necessary high C.E.D. The failure is not due to their polar groups having less attraction for the nitrile groups of the polymer than they have for their own kind. A modified equation for linking solvent power with the C.E.D. of the solvent in a semi-quantitative manner has been devised. This contains an arbitrary constant K, but the value of this varies only within narrow limits.

Measurement of the strength of steric barriers in non-aqueous polymer dispersions

Abstract: The forces of repulsion generated in the steric barriers of a series of monodisperse spherical polymer particles, varying in diameter, have been measured using a surface balance. The particles were stabilized using a graft copolymer with a poly(methyl methacrylate) backbone and heptane soluble poly(12 hydroxy stearic acid) side chains. It was established that the particles were supported on a water surface and that the stabilizing polymer was in a heptane phase in the plane of compression. From pressure-area measurements, a stabilizing barrier thickness of 130 A (independent of particle size) was found which was in good agreement with the value from viscometry. Compression of the particles at the interface permitted the measurement of the collapse pressure of the steric barrier from which the work done in compressing the barrier was computed. Two theoretical models for the system, one similar to Fischer's treatment of osmotic pressure changes associated with the overlap, or inter-penetration, of the steric barrier and another based upon Ottewill and Walker's treatment of the free energy of dilution of the steric barrier have been evaluated. Both models are in good agreement with the experimental data.

Some mechanical properties of a commercial polymethyl methacrylate

Abstract: The mechanical properties of thermoplastics are strongly interdependent and sensitive to changes of temperature and straining rate. These and other, less general, factors have an important bearing on the choice of testing techniques which can very often not merely be taken over from the established metal-testing practice. These points are discussed in detail, taking a few tests on the acrylic thermoplastic Perspex (polymethyl methacrylate) as instances. Some numerical values of the properties of Perspex in compression, tension, fatigue and impact are also given, mostly in graphical form.

The suppression of methane–air ignitions by fine powders

Abstract: The effect of the particle size of some inorganic materials on their efficiency as ignition suppressors has been studied. It has been found that there is a direct relationship between this efficiency and the surface area of the powder exposed to the advancing flame. Flame inhibitors have been placed in an order of efficiency on this basis. The alkali halides have been shown to have an efficiency which cannot be fully accounted for by the thermal characteristics of the powders, and an explanation is suggested.

The drawing of ‘terylene’†

Abstract: A method of analysis of continuous-drawing processes in terms of the basic load/extension/temperature properties of high polymers is given. Experimental work has been largely confined to polyethylene terephthalate (‘Terylene’ multi-filament yarn), for which material quantitative results are presented. This includes load/extension curves covering the temperature range in which uniform extension takes place, and results on ‘natural’ draw ratios when the extension proceeds by ‘necking’. A brief account of a theory of ‘cold-drawing’ is given.

The dealkylation of alkyl aromatic hydrocarbons I. The kinetics and mechanism of toluene decomposition in the presence of hydrogen

Abstract: The kinetics of toluene and xylene decomposition in the presence of hydrogen have been investigated under two sets of conditions: 500–600°/250 atm. and 700–950°/atmospheric pressure. The reaction is thermal and homogeneous and leads to simple products under these conditions provided that excess hydrogen is initially present. The kinetics are then of order 1.5: first-order with respect to toluene and order 0.5 with respect to hydrogen. In presence of excess hydrogen, the reaction is straightforward with the formation of benzene and methane. In the absence of excess hydrogen the kinetics and product compositions become complex and variable. Some possible mechanisms for the principal reaction (demethylation) in presence of hydrogen are discussed and attempts are made to explain qualitatively the effect of increased conversion on the reaction sequence postulated by Szwarc for decomposition in the absence of added hydrogen.

Gas chromatography. II. The separation and analysis of gas mixtures by chromatographic methods

Abstract: A rapid chromatographic method of gas analysis by elution development is described. A column of activated charcoal is used for the lighter gases such as hydrogen, carbon monoxide, methane, ethylene, ethane, and acetylene; and a gas-liquid partition column carrying ‘dinonyl’ phthalate as the stationary phase is employed for the heavier gases such as propane, propylene, and the C4 hydrocarbons.

Synthesis of poly(arylene sulfones) and poly(arylene ketones) by reactions involving substitution at aromatic nuclei

Abstract: The preparation of aromatic macromolecular structures by nucleophilic substitution reactions (A), in which polymerization proceeds via the formation of ether linkages, and by the electrophilic substitutions, (B) and (C), where sulfone or ketone linkages are formed is described.

Gas‐liquid chromatography in a plastics analytical laboratory

Abstract: This report gives an account of the application of gas-liquid chromatographic methods to the general work of a plastics analytical laboratory. Particular attention is paid to the examination of monomers, of depolymerization products obtained from polymers, and of adhesives. The use of dinonyl sebacate as the stationary liquid phase in a particular problem involving the determination of small amounts of methylcyclohexane in light petroleum (boiling range 60–80°) is described.

A new technique for polymer grafting

Abstract: Initiation of free-radical polymerization by metal carbonyl–organic halide systems has been extended to the case in which the halide component is a N-halogenated amide or alkylamide. Evidence is presented to show that the nitrogen atom becomes attached as a terminal group to the polymer chain. The halogenated amide group may form an integral part of a polymer. Thus, N-halogenated polymers may be used with metal carbonyls as initiating systems, so that this technique provides a new means of grafting vinyl polymers on to preformed chains containing CONH groups. Data presented for the grafting of a number of vinyl monomers on to polyamides, polypeptides, and natural proteins enable a detailed mechanism of grafting to be deduced.

Polymers from oxacyclobutanes II. The laboratory‐scale evaluation of the polymer from 3: 3‐bischloromethyloxacyclobutane

Abstract: The physical and mechanical properties of the polymer under various temperature conditions are studied in detail. The product has electrical properties very similar to those of polyethylene terephthalate and is mechanically intermediate between polythene and nylon.

The nature of the products obtained by refluxing styrene and drying oils in xylol solution. II.Additional data on the styrene-Tung oil reaction†‡

Abstract: An examination has been made of the reaction products obtained by refluxing a mixture of equal weights of styrene and tung oil in xylol solution in the absence of polymerization catalysts. Copolymerization occurs between styrene and tung oil. Saponification of the copolymer yields two main types of styrenated elaeostearic acid. One, which gives an insoluble potassium salt, contains styrene combined with elaeostearic acid in the approximate average molecular ratio of 8 : 1. The other styrenated acid, which is soluble in light petroleum and yields a soluble potassium salt, approximates in composition to a product derived from 1 molecule of styrene and 1 molecule of elaeostearic acid. In the conditions described, about 60% of the styrene remains unpolymerized and none forms a self-polymer. Only about 60% of the available elaeostearic groups take part in copolymer formation, the remaining 40% being recoverable in a styrene-free form. It is believed that the 1 : 1 styrenated acid is formed by a Diels-Alder mechanism.

Amine salts of polypyromellitamic acids

Abstract: The pyromellitamic acid prepared from pyromellitic anhydride and p:p′-diamino-diphenyl ether (the precursor of the heat-resistant polyimide) can be dissolved in aqueous organic bases to form solutions which, unlike those of the free acid dissolved in highly polar organic solvents, are resistant to hydrolytic degradation. These solutions on drying and heating evolve the base to yield the pyromellitimide polymer and can be employed in fabrication processes, particularly for the formation of films and surface coatings. Data are presented on the properties of the solutions and derived films.

The mechanics of bubble formation

Abstract: The size of gas bubble produced from an open-ended tube immersed in a liquid can be derived by equating surface tension and buoyancy forces. The equations do not apply, however, when the gas flow is large as in many industrial fermentations, and porous elements are therefore often used to provide many orifices and a low gas-flow through each. Even this technique fails if a mycelial growth is formed during the fermentation because the bubbles coalesce in the fermenter. Mechanical agitation was examined by the author by measuring gas-to-liquid transfer rates using paper pulp to imitate the mycelium, since this was found to interfere chemically with the reaction. Without agitation, the paper pulp reduced the transfer rate by a factor of twenty. With simple paddle agitation in conjunction with a sparge ring, the effect of pulp was reduced to a factor of seven but with a high-speed agitator used with an open tube gas inlet, the factor was reduced to two.

Thermodynamics of formaldehyde manufacture from methanol

Abstract: The production of formaldehyde from methanol, either by thermal decomposition, by catalytic oxidation or by a combination of the two, is treated as an exercise in chemical thermodynamics. Simple dehydrogenation of methanol does not appear attractive because it requires temperatures which tend to produce decomposition of the formaldehyde as it is formed. Oxidation of methanol to formaldehyde and steam requires the agency of a catalyst which is active in the region of 300°, the ideal working mixture for an insulated catalyst containing roughly 5 1/2 to 8% of methanol in air. The composite process, in which dehydrogenation and oxidation occur simultaneously, offers certain advantages, and may be expected to give maximum efficiency in the range 500–700°, corresponding to methanol/air mixtures containing 45 to 37% of methanol. Addition of steam to the reacting mixture lowers the catalyst temperature and modifies the product composition accordingly. Rapid cooling of the products to about 300° is essential to avoid regeneration of methanol and decomposition of formaldehyde. An interesting feature is that the straight oxidation-process operates with mixtures of methanol and air at or just below the lower inflammability limit, whereas the composite process requires mixtures at or above the upper inflammability limit.

The dealkylation of alkyl aromatic hydrocarbons. II.—The dealkylation of coal tar naphthas†

Abstract: The thermal dealkylation of toluene, xylene, vertical-retort and coke-oven naphthas has been studied at 100 atmospheres pressure in the presence of hydrogen at temperatures in the range 540–660°. The experiments with toluene were carried out to check the kinetics already proposed1 in this new experimental region. The rate constants, calculated on the basis of a 1·5-order reaction from the results now obtained, were found to be lower than anticipated by extrapolation of the results obtained in the first part of this series. This discrepancy is discussed and results from two other sources have been used to calculate rate constants at intermediate and lower temperatures in an attempt to clarify the position. The experiments with the 5° xylole and the vertical-retort naphtha show that it is possible to convert the polymethylbenzenes almost completely to benzene and toluene at temperatures in the region of 650°. The paraffinic materials in these feedstocks are cracked to gas. The formation of higher-boiling materials can be limited by using high molar ratios of hydrogen to hydrocarbons. The experiments with the coke-oven feedstocks show that these materials are very stable under the above experimental conditions. This stability is directly related to the low concentration of alkylated aromatic hydrocarbons which occur in these naphthas.

The application of distance distribution functions to structural analysis of core–shell particles

Abstract: The structure of core–shell latex particles of polymethylmethacrylate (the core) and polyurethane (the shell) have been investigated by methods of small-angle X-ray scattering (SAXS) and atom-force microscopy. A set of SAXS patterns has been obtained using contrast variation method. Indirect methods have been used to follow the evolution of distance distribution functions from SAXS for lattices in various sucrose solutions over a range of solution density, yielding structural parameters of the particles such as core size, shell thickness and density of the polymers including density deviations within the particle's core and shell. A model for an ensemble of core–shell particles with a normal distribution of average electron density of both the core and the shell has been developed to fit the distance distribution functions using a random search algorithm. The effects of nanophase separation in the polyurethane is estimated using Monte Carlo simulations of the distance distribution functions where the phase-separated polyurethane is represented by spherical truncated cones in a shell simulating the location of hard and soft polyurethane blocks, respectively.

Homo- and copolymerization of vinyl phosphates and phosphonates

Abstract: Phosphorus–containing monomers of general formulae homopolymerized, copolymerized with methyl methacrylate, vinyl acetate, and styrene under a variety of conditions, and the products were characterized. The results of homopolymerization show that yields and the degree of polymerization depend on the purity of the monomers, method of polymerization, and the initiator used. With the exception of monomers containing β-chloroethoxy group attached to the phosphorus atom, polymers obtained from the dialkyl vinyl phosphates had higher molecular weights than the corresponding dialkyl vinyl phosphonates. Dialkyl isopropenyl phosphates polymerized less readily than the dialkyl vinyl phosphates and diethyl styryl phosphate did not polymerize at all. An attempt is made to explain these results in terms of steric hindrance, charge distribution, and chain transfer. Examination of the copolymerization products, with a number of techniques used, indicates that these consist of polymers with a wide range of compositions and molecular weights. The copolymers with methyl methacrylate appear to consist of a large block of poly(methyl methacrylate) at one end and a smaller block of polymer formed from the vinyl phosphate or phosphonate at the other. Similar conclusions are drawn about copolymers involving styrene. It is likely that the monomer units in copolymers with vinyl acetate are randomly distributed.

Structure‐activity relations of β‐adrenergic agents

Abstract: A review of the structure-activity relations in aryloxypropanolamine β-adrenoceptor drugs is presented. The effect of substitution in various parts of the molecule on β1/β2 selectivity and degree of partial agonism is discussed. Cardiac (β1) selectivity is achieved by hydrophilic compounds with either p-amide substitution in the aryl ring, or a hydrogen bonding group in the amine side chain. Lipophilic compounds with branched chains tend to be β2 selective. Partial agonist activity may also be controlled by hydrogen bonding groups in the side chain and by aromatic substitution. Here 3,4-dihydroxyl groups give full agonists, mono-and des-hydroxy (OH) groups partial agonists. The size of any o-substituent is critical and a plot of Taft's steric factor versus partial agonism gives a linear relation. By manipulation of the above factors all combinations of selectivity and agonist activity may be achieved.

The chemical denaturation of groundnut protein and fibre formation

Abstract: Two types of denaturing agents, (a) urea, guanidine salts and related compounds and (b) amines, have been investigated with groundnut protein for fibre formation. The considerable rise in the viscosity increment of the protein on denaturation with urea and the hydrochloride and thiocyanate of guanidine, and with bases of dissociation constant higher than 10−4, has been interpreted in terms of increased asymmetry of the protein molecules, and only where such a rise was observed could solutions of the protein with the denaturant be prepared suitable for extrusion into fibre.