Showing papers in "British Polymer Journal in 1972"

Principles of action of polymeric flocculants

Abstract: The relationship of flocculation by water-soluble polymers to the classical phenomena of colloid chemistry is pointed out and the contributions of electrostatic and non-electrostatic forces are discussed. Modern flocculants have a high degree of polymerization (e.g. c. 50 000) and an extremely extended configuration when dissolved in a favourable solvent; this factor explains qualitatively some of the peculiarities of flocculation by polymers and indicates the need for rational control of their use if optimum results are to be achieved. It is concluded, however, that a quantitative theory of specific flocculant systems is not possible at present. Future developments in flocculation technology will almost certainly include introduction of cheaper or more selective flocculants, improved control through the use of auxiliary reagents and more sophisticated consideration of the surface chemistry of materials that have to be flocculated.

Nitrogen-containing products from the thermal decomposition of flexible polyurethane foams

Abstract: The thermal decomposition of a polyester and a polyether flexible foam in a nitrogen atmosphere has been studied by gas chromatography, mass spec-trometry and elemental ultramicroanalysis. It is shown that the decomposition behaviours of the two foams are similar. At low temperatures (200 to 300 °C) there is a rapid and complete loss of the tolylene diisocyanate unit of each foam as a volatile yellow smoke leaving a polyol residue. The smoke has been isolated as a yellow solid (common to both foams) which contains virtually all of the nitrogen of the original foams and, under the conditions of test, is stable at temperatures up to 750 °C. Nitrogen-containing products of low molecular weight (mainly hydrogen cyanide, acetonitrile, acrylonitrile, pyridine and benzonitrile) observed during the high temperature decomposition (over 800 °C) of the foams are shown to be derived from the yellow smokes. At 1000 °C, approximately 70% of the available nitrogen has been recovered as hydrogen cyanide.

Kinetic investigation of the synthesis of a polyethersulphone

Abstract: This paper summarises results obtained from a kinetic investigation of the processes occuring during the synthesis of polyethersulphones by reactions such as: The factors determining the variations in functional group reactivities due to ‘bridge’ effects are described with reference to the reactivities of these groups in model systems, and the detailed kinetics shown by the polycondensations are explained. Evidence is presented to show that ether interchange can occur in a manner analogous to ester interchange in a polyesterification, and that in polycondensations where potassium fluoride (as opposed to the chloride or bromide) is eliminated chain extension is reversible and the use of high reactant concentrations is required to obtain polymers of high molecular weight.

Structure and permeability of porous films of poly(hydroxy ethyl methacrylate)

Abstract: Porous films of poly(hydroxy ethyl methacrylate) have been made by photo-polymerisation of solutions of the monomer. The permeability of homogeneous films depends on the cross-link density and the concentration and composition of the polymerisation solvent. A membrane of minimum water permeability, in which the transport mechanism is principally diffusion, results from a cross-link concentration of ∼9.4 mol-% and a monomer concentration of ∼75% in an aqueous ethylene glycol solvent (20% ethylene glycol). More porous (macroporous) films were prepared by first cooling the solution such that the solvent freezes and the monomer occupies the interstices between the solvent crystals. After polymerisation and removal of the solvent, a porous structure results. The rate of freezing, the profile of the thermal gradient, and the solvent and crosslinker concentrations control the permeability of this film. Slow cooling gives random pores (K ≃6 × 10−15 cm2), but rapid, directional cooling from one face gives oriented pores with K ≃10−12 cm2. A 6-order change in K results from varying the monomer concentration from 40 to 85% in a 4:1 water: ethylene glycol solvent, and a 3-order change from increasing the ethylene glycol content of the solvent from 0 to 40% at a fixed monomer concentration.

The effects of pressure and temperature upon the viscosities of liquids with special reference to polymeric liquids

Abstract: From a consideration of the work required for expansion of a liquid, the following relationship between viscosity η, pressure P and temperature T is put forward. For unassociated liquids with molecules which are not too large, V* is taken as the parachor, log10 (η* in Ns/m2) is −3.88, P* is 8.58 × 106 N/m2, R is the gas constant, and T* is a constant characteristic of each liquid. The equation can be applied to polymeric liquids if V* and η* are taken as disposable constants. For example, for polystyrene V* is found to be 3 × 10−3 m3 mol−1 and log10 (η* in Ns/m2) to be 3.4 log10Mw −10.2 where Mw is the weight-average molecular weight (kg/mol) from 5 kg/mol upwards. In the equation, the same constants serve for the variation of viscosity with pressure and with temperature. The viscosity under a high pressure can therefore be estimated from viscosities all measured at normal pressures but at different temperatures. The viscosities of a number of polymers have been measured over a range of temperature and pressure and the results support the equation. Support is found for the view that segments are involved in the flow of polymeric liquids and V* gives a measure of the volume of the segment. The size of the segment seems to increase as the flexibility of the polymer chain decreases. The lowest values for V* are found for polysiloxanes in which the segment seems to be only four atoms long. Larger values of V* are found for polymers with units of the type –CH2–CHR-. Larger values still of V* are given by polymers with units of the type –CH2-CR1R2- and even larger V* values are found for those polymers with benzene rings constituting a major part of the main chain. As V* rises the viscosity of the polymeric liquid becomes much more dependent upon pressure and temperature. Thus whilst the polysiloxanes have viscosities which are relatively insensitive to pressure and temperature, the aromatic polysulphones and poly(2,6-dimethylphenylene oxide) have viscosities which are very sensitive to pressure and temperature.

Stabilisation of polyacrylonitrile by oxidative transformation

Abstract: The changes occurring during the heat treatment of polyacrylonitrile polymers in the presence of air up to 350 °C have been examined using both physical and chemical techniques. It is concluded that substantial oxidation does not occur until the polymer has been converted to a ladder structure containing readily oxidisable methylene groups. The development of the highly characteristic physical behaviour of the oxidised polymer, notably absence of melting and hydrophilicity, is associated with the formation of a strongly hydrogen bonded polydihydropyrid-4-one structure which acts as an internal restraint to molecular motion and permits the orientation of the parent polymer to be carried through to the higher temperature pyrolysed carbon fibre.

Toxic products from the combustion and pyrolysis of polyurethane foams

Abstract: Products from the thermal decomposition of four polyurethane foams heated to temperatures in the range 220 to 400 °C, in atmospheres of nitrogen, of 6% oxygen in nitrogen and of air were examined for some of the anticipated toxic materials. When phosphorus-containing inhibitors were added to or chemically incorporated in the foams, phosphorus compounds were evolved under most of the conditions employed. Other materials detected were hydrogen cyanide, isocyanate, urea, halogenated compounds and alkenes. A brief discussion is given of the hazard presented by polyurethane foams decomposing under these conditions.

Siloxane modification of polyamides

Abstract: 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.

The use of high molecular weight polyacrylamides in the selective flocculation separation of a mineral mixture

Abstract: Most of the conventional mineral processing separation methods are not effective on mineral mixtures that contain a large percentage of slimes. Selective flocculation is a potentially attractive process for treating such mixtures. The process relies on achieving conditions under which the polymer flocculant adsorbs onto the surface of one mineral and not on the others. In a practical system this selective adsorption would have to be achieved under conditions of fluctuating water quality and mineral composition. Partially hydrolysed polyacrylamides with a molecular weight of around 3 × 106 have been used in the selective flocculation separation of a synthetic finely-divided mixture of haematite and a silicate (100% < 20 μm). It was possible to flocculate selectively from the mixture either the haematite or the silicate by using polyacrylamides of differing anionic character. It was usually necessary to employ a 1:1 electrolyte and a dispersant, in addition to the flocculant, to achieve good selectivity in this system.

Calibration procedures in gel permeation chromatography

Abstract: Procedures for the determination of the log molecular weight vs. elution volume calibration relation are reviewed for linear homopolymers. The calibration curve is readily established with narrow molecular weight distribution fractions. For broad molecular weight distribution fractions the peak molecular weight at the peak elution volume of a fraction's gel permeation chromatogram has to be calculated from average molecular weights. When well-characterised fractions of the polymer requiring analysis are unavailable, a calibration curve can be established by procedures which assume that the hydrodynamic volume of a polymer molecule in solution controls fractionation in gel permeation chromatography. These universal calibration procedures require information on Mark-Houwink viscosity constants or polymer unperturbed dimensions. The validity of hydrodynamic volume as the universal calibration parameter is discussed with special reference to the goodness of the solvent for a polymer and polymer polarity. Examples are given of the various calibration procedures which are employed in the determination of molecular weight distribution and average molecular weights for poly(methylmethacrylate), polyethylene and polyisoprene.

Sequence length and crystallinity in alpha‐olefin terpolymers

Abstract: The minimum sequence length for crystallisation in a polymer was determined by a novel kinetic approach using sequence analysis of a series of blocky terpolymers. Copolymers and terpolymers of ethylene, propylene, and but-l-ene were prepared with a Ziegler–Natta catalyst system. Compositions of feeds and polymers were analysed, and kinetic reactivity parameters were calculated using both the Fineman–Ross and Alfrey–Goldfinger approaches. The parameters were then applied to determine the sequence length distribution of each component in the terpolymers. Also, deliberate control of sequence lengths enabled synthesis of heptane-soluble, rubbery polymers even using a catalyst system which normally produced blocky materials. Crystalline contents of the terpolymers were determined experimentally by nitric acid digestion. A critical comparison of the measured crystallinities with the calculated sequence length distributions was thereby made possible. From this comparison a minimum sequence length of monomer below which crystallisation did not occur was estimated; this length was approximately 20 backbone carbon atoms.

Structural characterisation of some polystyrene—polyisoprene copolymers

Abstract: The various levels of organisation which may be distinguished in non-crystalline block copolymers are considered. An account is given of the application of low-angle X-ray diffraction and electron microscopy to the characterisation of the two-phase morphology and grain texture of some styrene/isoprene copolymers. The first group of copolymers to be considered contains two series of samples of the type S–I, (S–I–)2X, (S–I–)3Y, and (S–I–)4Z where I is polyisoprene, S polystyrene and X, Y and Z are di-, tri- and tetra-functional coupling groups. The second group of copolymers which was subjected to a less detailed study than the first consists of just two polystyrene-g-polyisoprene samples.

The effect of a secondary process on the course of polymer crystallisation

Abstract: The possibility that the presence of several processes occurring during the crystallisation of polymers may account for anomalous constant fractional values of the Avrami exponent is reconsidered, and for various reasons rejected. Experimental isotherms exhibit systematic variations when analysed as two stage processes, which can only be accounted for by fractional n values of no theoretical significance. An explanation for these deviations must be sought in the mechanism of spherulitic crystallisation, and in particular the mechanism of branching and impurity rejection of the basic fibrillar units.

Flammability of polymers. v. thermal volatilisation analysis of polyester resin compositions

Abstract: Thermovolatilisation analysis has been used as part of an investigation of the flammability of an insaturated polyester resin. It was clearly possible to distinguish two reaction stages which were attributed to breakdown of the styrene and polyester chains respectively and in neither case did flame retardants affect the reaction very much.

An extension of polymer crystallisation kinetics to a branching mechanism for spherulitic growth

Abstract: The initial stages in the development of spherulites from primary nuclei to spherical arrays of branching fibrils are included in the kinetics of polymer crystallisation. Since most of the experimental isotherms exhibit the required time dependence only over a limited range it is considered that the model has little use, and these initial stages in the development of spherulites have little effect on the degree of fit of the experimental isotherms to the Avrami rate equation. The general time dependences of crystallisations developing as a branching process is outlined and compared with that of the Avrami equations for growth of spherical particles.

Parameters affecting the performance of polyelectrolytes as aids to water clarification

Abstract: An investigation of the flocculation of silica and alumina suspensions by a series of synthetic flocculants of a wide range of charge density both anionic and cationic in nature has been carried out. The extent of flocculation was determined by measurements of settling rate, sediment volume and supernatant clarity. The effect of the pH of the suspension on the performance of a number of selected polymers has been investigated. In the systems examined, flocculation was largely controlled by the charge carried by the suspended particles and polymer molecules. The dosage/settling rate characteristics of kaolin suspensions flocculated with non-ionic polymers of varying molecular weight are reported. The dosages of non-ionic polymers required for optimum flocculation of kaolin suspensions of varying solids content have been measured. At low particle concentrations bridging is less effective, and is probably reduced due to the adsorption of polymer molecules on to single particles.

The laboratory evaluation of polyelectrolyte flocculants

Abstract: The application of polyelectrolyte flocculants as primary coagulants, coagulant aids and sludge conditioners in the treatment of water for public supply is discussed. Laboratory techniques that have been used to evaluate commercial polyelectrolytes for these uses are described and exemplified with results. The difficulty of defining floc characteristics is emphasised.

Investigations into the behaviour of “plumbonacrite” basic lead carbonate as a thermal stabiliser for polyvinyl chloride

Abstract: An apparatus is described which permits reasonably uniform heat treatment of fairly large samples of PVC blends in controlled atmospheres, at preset temperatures, and for predetermined lengths of time. Experiments are described in which portions of a plasticised PVC blend, and also portions of an unplasticised PVC blend, were heated under nitrogen at 180 °C for various lengths of time up to those stages when Congo Red tests showed hydrogen chloride to be liberated. Each blend contained the basic lead carbonate “plumbonacrite”, 6PbCO3. 3Pb(OH)2.PbO, as stabiliser, and stearic acid as milling lubricant. Carbon dioxide evolved during the stabilising reactions was measured, and the crystalline solids in each heated PVC blend sample were studied by X-ray diffraction. The results obtained show that the plumbonacrite stabiliser in each PVC blend was used continuously and completely during the effective stabilisation period. The rates of carbon dioxide evolution were found to differ markedly between the plasticised and unplasticised blends, but in each case they could be described in terms of first order reaction kinetics. Correlation of these carbon dioxide measurements with the X-ray diffraction results led to the conclusion that the stabilising reactions in the plasticised PVC blend took place mainly in solution, whereas these reactions in the unplasticised PVC blend seemed to take place within the plumbonacrite crystals themselves. It is shown that these findings are consistent with previous work in these laboratories which has led to the idea that soluble lead compounds are formed by reaction of the basic lead stabiliser crystals with stearic acid milling lubricant, and that these compounds are in some way responsible for stabilising polyvinyl chloride against thermal decomposition. Further, it is suggested that the present results show that basic lead compounds act as thermal stabilisers for PVC in the true sense of the word. Considering in particular a radical chain mechanism for the thermal dehydrochlorination of polyvinyl chloride, a theory is proposed which explains how basic lead compounds can stabilise this polymer.

Thermodynamic parameters of polystyrene solutions in cyclohexane, determined from sedimentation—diffusion equilibria in the ultracentrifuge. dependence on concentration, temperature and molecular weight

Abstract: Determination of the sedimentation–diffusion equilibrium is one of the methods furnishing data on the thermodynamic parameters of polymer solutions. By means of this procedure measurements can be performed over a considerable range of concentrations. The equilibria in the ultracentrifuge have been determined for five polystyrene samples of narrow distribution covering the molecular weight range 2 × 104 to 2 × 106, at concentrations up to 40 wt-% and at temperatures of 30, 45 and 65 °C. The results are expressed in the data for the chemical potential of the solvent, the number-average chemical potential of the polymer and the interaction parameter ξ. The results are compared with those obtained from osmotic pressure, light scattering and critical miscibility measurements. At very low concentrations the molecular weight dependence of the interaction parameter is in agreement with literature values derived from osmotic pressure and light scattering figures. At higher concentrations this molecular-weight dependence decreases sharply but remains noticeable up to 40% concentration.

The polymerisation of styrene on 13X zeolite

Abstract: The polymerisation of styrene on 13X zeolite at 30°C has been studied. Rates of monomer consumption were determined dilatometrically, and the molecular weight distributions of the product were investigated by gel permeation chromatography. The effects of varying the weight of zeolite and the concentration of styrene were studied; the effects of preheating the zeolite samples to two different temperatures were also investigated. A cationic mechanism for the polymerisation is proposed; the initiation is on the zeolite surface and involves adsorbed water. The available space in the vicinity of the sites activated by water appears to determine the rate of propagation, and the molecular weight of the polymer.

trans-polypentenamer: A general purpose rubber from a novel reaction

Abstract: The nature of the catalysts for the ring-opening polymerisation of cycloolefins is reviewed with particular reference to the production of trans-polypentenamer. The roles of the components of the catalyst systems are discussed and a mechanism for the ring-opening polymerisation of cycloolefins is proposed.

Fifty years of polymer research

Abstract: The writer summarises his researches in the field of polymer science. He began with studies of the structures of space-network and sheet polymers in crystals. Currently he is working on the structures of macro-ions in silicate and borate crystals and glasses and on the development of a new theory of structures and thermodynamic properties of (polymer and other) solutions.

Effect of annealing on transport properties of organic vapours in drawn polyethylene

Abstract: Drawing of quenched polyethylene at 60°C transforms the spherulitic sample into a material with fibrous structure. As a consequence, the sorption and still more the diffusion of C2Cl4 vapours are drastically reduced. Annealing at 120 and 125°C increases the crystallinity and hence reduces the amount of the amorphous component. In spite of that, it enormously increases the transport properties. It restores the sorption per unit volume of amorphous component to a value which, corresponding to completely relaxed amorphous component, is even higher than that of the starting undrawn but quenched material. The diffusion constant after annealing is a little smaller than in the undeformed original sample and shows the same small dependence on concentration in striking contrast with the drawn material. One concludes that the restoration by annealing of the sorption and diffusion coefficients for drawn polyethylene to the values of the undrawn material is a consequence of the complete relaxation of polyethylene chains, in particular of tie molecules, in the amorphous component which completely overcompensates the effects of a reduced amorphous fraction and the increase in crystal perfection.

High pressure polymerisation of acetylenic compounds

Abstract: Acetylenic compounds have been polymerised by heating at pressures up to 23.5 kbar in the absence of initiators. The products are either low melting or intractable solids. 2-Butyne copolymerises with tetramethylethylene and trimethylethylene. Propiolic acid gives carbon dioxide and a mixture of aromatic acids as well as an amorphous polymeric acid.

Separation of polymer and copolymer mixtures by means of a disc centrifuge

Abstract: By means of a disc centrifuge it is possible quickly and easily to separate the components of particulate mixtures of polymers and copolymers having different densities. The technique has been applied to mixtures and copolymers of PVC and PMMA, and PE and PVAc, but is believed to be of general application.

The effect of boiling water on an amorphous aromatic polyamide

Abstract: Amorphous poly(sulphonyldi-p-phenylene-α,ω-alkylene dicarboxamides) undergo marked changes during immersion in boiling water. This treatment produces opacity, softening and ultimately blistering and embrittlement of moulded or cast specimens produced from these polyamides. These changes have been shown to be due to a lowering of the glass-transition temperature (Tg) to below 100 °C, and to the acid catalysed, hydrolytic scission of in-chain amide bonds. The stability to boiling water is improved by copolymerisation to raise the Tg and by minimising the total acid content of the polymers. An n.m.r. method for the determination of terminal amine groups in these polyamides is described.

Mechanical properties of fibers of linear poly(ester urethanes) and poly(ether urethanes) in relation to details of their chemical structures

Abstract: Elastic fibres soluble in dimethylformamide were made from essentially linear polyester- and polyetherurethanes. The molecular structures of the polyurethanes were varied by using as chain extenders aliphatic diamines with a successively increasing number of carbon atoms. Mechanical investigations resulted in modulus, stress relaxation and creep data which oscillated with increasing number of carbon atoms of the diamines used. These results and the temperature- and time-dependence of these data can be explained by a model proposing the existence of hard segment domains in a matrix of soft but crystallisable polyester or polyether material.

Application of europium and praseodymium shift reagents to the n.m.r. spectra of polymers

Abstract: The use of Eu(fod)3 and Pr(fod)3 shift reagents for the investigation of the nuclear magnetic resonance spectra of polymers is reported for the following samples: poly(vinyl methyl ether), poly(vinyl ethyl ether), poly(vinyl acetate) and poly-(propylene oxide).

The characterisation of polyolefins using a curie‐point pyrolyser and gas chromatography

Abstract: The products of controlled thermal degradation of polyolefins have been examined by gas chromatography. The factors determining the formation of decomposition products in the Curie-point pyrolyser have been studied and a highly reproducible distribution of products has been obtained at a pyrolysis temperature of 595 °C. The probable degradation mechanisms are discussed and a diagnostic scheme has been derived for determining from the degradation products the nature of the branches and thus identifying the comonomer in an ethylene copolymer.