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Shell Chemicals Limited Fundacao Calouste Gulbenkian – FCG Fundacao para a Ciencia e Tecnologia - FCT

Conductivity of lithium triflate dissolved in silica/PEO composites is reported. The amount of silica added to the films varies between 7% and 24%, high and low molar mass PEO samples are used as co-composite materials. Measurements indicate good conductivity coupled with good physical properties over a range of temperatures.

Preparation of the polymer blends using emulsion polymerisation is reported. This is a novel technique for producing interpenetrating networks of methacrylate polymers which are stabilised only by physical interaction. Glass/rubber transition data is recorded.

Reaction of a range of bis(ylides) with acid chlorides has been used to prepare the bis(oxoylides) 11–15 . Similarly a range of simple ylides react with bis(acid chlorides) to give bis(oxoylides) 19–27 with the isomeric structure. Flash vacuum pyrolysis (FVP) of one example of the first type results in extrusion of Ph 3 P rather than the expected Ph 3 PO while six examples of the second type do extrude Ph 3 PO upon FVP at 500 °C to afford the bis(alkynes) 28 . Examples of the corresponding bis(tributylphosphonium ylides) have also been prepared but attempts to construct a tetrakis(oxoylide) 31 using a stepwise approach were unsuccessful. Fully assigned 13 C NMR spectra are presented for six of the bis(oxoylides).

The phosphorescence lifetime of carbazole in various homopolymer matrices was found to be highly dependent on additive concentration, temperature and supporting matrix. A partially deuterated polystyrene matrix caused a decrease in lifetime relative to that obtained for carbazole in the absence of deuterated species, and no significant quenching occurred on the addition of 3-bromocarbazole and Pr[18-crown-6](NO 2 ) 3 to the films. The results have been interpreted in terms of energy transfer from the additive to the polymer, and, in the case of the deuterated matrix, the possibility of energy migration is proposed.

The kinetic compensation effect was investigated for a great variety of polymers, showing its existence for a homogeneous solid state decomposition.

The results of an investigation of a polymer electrolyte system based on the poly(trimethylene carbonate) host matrix, designated as p(TMC), with lithium tetrafluoroborate guest salt are described in this presentation. Electrolytes with lithium salt compositions with n between 3 and 80 (where n represents the number of (O=COCH2CH2CH2O) units per lithium ion) were prepared by co-dissolution of salt and polymer in anhydrous tetrahydrofuran. The homogeneous solutions obtained by this procedure were evaporated, within a preparative glovebox and under a dry argon atmosphere, to form thin films of electrolyte. The solvent-free electrolyte films produced were obtained as very flexible, transparent, completely amorphous films and were characterized by measurements of total ionic conductivity, cyclic voltammetry, differential scanning calorimetry and thermogravimetry., Shell Chemicals Limited. Fundação para Ciência e Tecnologia. Fundação Calouste Gulbenkian.

The results of a preliminary investigation of a series of polymer electrolytes based on a novel polymer host, poly(trimethylene carbonate) or p(TMC), with lithium triflate or lithium perchlorate and various plasticizing additives, are described in this presentation. Electrolytes with lithium salt compositions of about n = 10 (where n represents the molar ratio of (O=COCH2CH2CH2O) units per lithium ion) and additive compositions between 5 and 15 wt% (with respect to p(TMC)), were prepared by co-dissolution of salt and polymer in anhydrous solvent with a controlled amount of additive. The homogeneous solutions obtained were evaporated within a preparative glovebox and under a dry argon atmosphere to form thin films of electrolyte. The solvent-free electrolyte films produced were characterized by measurements of total ionic conductivity, differential scanning calorimetry and thermogravimetry. In general the triflate-based electrolytes were found to show moderate ionic conductivity and good thermal stability while perchlorate-based electrolytes showed higher levels of conductivity but lower thermal stability. Electrolytes based on this host polymer, with both lithium salts, were obtained as very flexible, transparent, completely amorphous films., Fundação para a Ciência e a Tecnologia (FCT), Shell Chemicals Ltd

In this paper, the results of preliminary studies of two new solvent-free polymer electrolytes based on poly(trimethylene carbonate), p(TMC), with lithium trifluoromethanesulphonate, (triflate), and lithium perchlorate are described. Thin films of these electrolytes were obtained by evaporation of solvent from homogeneous mixtures of known masses of host polymer and salt. Electrolytes with compositions of n between 1.5 and 85, where n represents the molar ratio of (OCOCH2CH2CH2O) units per lithium ion, have been prepared. These solvent-free electrolytes were characterized by measurements of total ionic conductivity, differential scanning calorimetry (DSC) and thermogravimetry (TGA). As expected from previous studies with these salts in poly(ethylene oxide), PEO, the triflate-based system showed superior thermal stability but with a lower total ionic conductivity than that of the perchlorate-containing electrolyte. The highest conductivity (approximately 3×10−4 Ω−1 cm−1) was found at 95°C with the electrolyte composition of (TMC)2LiClO4., Fundação para a Ciência e a Tecnologia (FCT), Shell Chemicals Ltd

Mathematical modelling of the oxidation of a polymer, based on Fick's Law for diffusion of oxygen with reaction, with suitable boundary conditions produced an equation which combines the diffusion-free kinetics of the surface layers of the oxidising sample with the diffusion-controlled kinetics which predominate at greater depth. Comparison of the final, simplified, equation with literature results for oxidation rates versus film thickness showed excellent agreement with experiment. Attempts to fit to the experimental results an equation which assumes diffusion control from the film surface failed, indicating that the splitting of the film into two domains for the purpose of kinetic investigation was correct.

The oxygen/ethane and oxygen/1-butene reactions have been investigated in a continuous flow system at atmospheric pressure over a manganese oxide/carbon fibre catalyst. The products of reaction were carbon dioxide and water. Apparent activation energies were 108 ± 4 kJ mol−1for the former reaction from 673 to 573 K, and 81 ± 4 kJ mol−1 for the latter from 573 to 473 K. Kinetic data for both reactions were best described by the rate equation:[Formula: see text]The surface mechanism may be complex and it is proposed that reactants interact as adsorbed species each of which is adsorbed on two surface sites. Both oxygen and the hydrocarbon gas appear to be directly involved in further steps. Scanning electron microscopy, X-ray photoelectron spectroscopy, and low temperature krypton adsorption were used to assess the catalyst structure.

Quenching of excimer fluorescence from polystyrene and monomer emission from 5 and 10% methyl methacrylate copolymer with styrene has been studied in solution using dibromoethane and iodine as quenching species. From the measured rate constants along with polarization measurement of the emissions, it is concluded that energy migration does not occur in dilute solution of polystyrene. It is proposed that excimer is formed by rotation of a pendant, excited phenyl group with a face-to-face conformation with its nearest neighbour.

A study has been carried out into the interaction of hydrogen halide gases with the polyene systems present in thermally degraded poly(vinyl acetate). Highly coloured products were formed during a dark reaction at 20°C and experimental results indicated a continued deacetylation reaction catalysed by hydrogen halide. A mechanism, involving the double bonds of the polyene systems, has been put forward to explain these results.

For a purified sample of poly(vinyl chloride), it is found that radiation of wavelength less than 300 nm causes dehydrochlorination. It appears that polychromatic radiation yields a constant ratio of concentrations of polyenes, even from the very early stages of reaction. It is proposed that energy transfer is an important step in the photodecomposition of poly(vinyl chloride).

Polyacrylamide has been synthesised at the surface of carbon fibre by the technique of electropolymerisation. Some details of the polymerisation have been presented and a preliminary proposal made for the mechanism responsible. The characterisations of carbon fibre and its surface have always presented a problem; in this work torsional braid analysis has been used to study the polymer present on the surface of the fibre.

Hindered amines are known to act as good photo-oxidative stabilizers for polymers, but controversy still surrounds the mechanism whereby this is achieved. The significance of complex formation between hindered amines and hydroperoxide groups in the mechanism is questioned, and the inability of hindered amines, or their nitroxide derivatives, to act as excited state quenchers is demonstrated. A mechanism involving complexation of trace transition metal impurities is proposed to account for the photo-stabilizing ability of these compounds.

The conductances of LiClO 4 and LiCF 3 SO 3 solutions in a low mol. wt polyether have been measured as a function of salt concentration. The results have been interpreted in terms of ion pair and triplet formation. It is concluded that, at the electrolyte concentrations normally used to form “polymer electrolytes”, most of the salt is present as ion pairs and that the conducting species are likely to be triplets and higher charged aggregates rather than single ions.

The products of the thermal decomposition of a series of copolymers of structure with n = 0, 1, 3, 4 and 5, have been investigated. A high proportion of the products consists of low molecular weight analogues of the parent polymers, with styrene the major constituent of the volatile liquids. The copolymers are more stable than head-to-tail polystyrene. Some general conclusions are drawn on the overall mechanism of breakdown.

Apparent changes in weight recorded by a mass-flow balance during experiments carried out by heating samples near, but not on, the balance platform have been ascribed to pressure gradients developing around the platform. The extent of such changes varies with the design of the balance system and the effect has also been observed using a micro-balance and a suspension balance mechanism.

The reaction of atomic oxygen and singlet oxygen molecules with films from various polymeric substrates was studied. The polymers used were poly(vinyl chloride), polyacrylonitrile, polystyrene, nylon 66, and poly(ethylene terephthalate). Atomic oxygen reacted readily with all of these polymers. The reaction was confined to the surface layers which results in the polymer films becoming more hydrophilic. No change was observed in the contact angle of water with films of poly(vinyl chloride) and polystyrene after they had been exposed to singlet oxygen molecules for several hours. Die Reaktion von atomarem und von Singulett-Sauerstoff mit Filmen aus verschiedenen Polymeren wurde untersucht an Polyvinylchlorid, Polyacrylnitril, Polystyrol, Nylon 66 und Polyathylenterephthalat. Atomarer Sauerstoff reagierte leicht mit den genannten Polymeren. Die Reaktion beschrankte sich auf die Oberflache, was dazu fuhrte, das die Polymeren hydrophiler wurden. Der Kontaktwinkel von Wasser mit Filmen von Polyvinylchlorid und Polystyrol zeigt nach mehrstundiger Einwirkung von Singulett-Sauerstoff keine Anderung.

Experiments have shown that hindered amine light stabilisers (HALS) are able to complex strongly with transition metal ions. During this reaction, in air, there is a marked tendency for oxidation of the metal ion species and the reaction is shown to be general across the first transition series. Using these results, in addition to evidence from other work, a scheme is proposed whereby these HALS, because of their complexing ability, will act as photo-oxidation stabilisers for polymers. Preliminary results show that HALS are also able to complex with non-transition metals.

The kinetics of the thermal decomposition of a series of copolymers of structure with n = 1, 3, 4, 5, 6 and 10 have been studied. Activation energies have been calculated for all the copolymers at various stages of decomposition. Apart from the n = 1 sample, the copolymers have similar values for the activation energy of the overall reaction. Surveys of stability using programmed and isothermal thermogravimetry both showed the same trends in behaviour.

Preliminary results are reported for the electrochemical synthesis of compounds formed by carbon fibre which are analogous to the ‘synthetic metals’ based on graphite and polyacetylene.

The photolysis of polystyrene in solution and in films has been studied using radiation greater than 300 nm in the absence of oxygen. Chain scission was observed for a free-radical polymerised sample and a sample prepared by anionic polymerisation in solutions of chloroform, but not in films unless traces of solvent were present. It is proposed that the species responsible for initiation of the scission reaction is a molecular complex between polymer and solvent.

Conductivity and n.m.r. measurements are reported for three poly(ethylene oxide)-inorganic salt complexes: PEO-LiCF3SO3-NaI ([EO]/[Li]/[Na] = 8/1/1), PEO-LiCF3SO3 ([EO]/[Li] = 4), and PEO-NaI ([EO]/[Na] = 4). The mixed-salt system was shown to have a larger amorphous phase content than either of the single-salt systems and more potential charge carriers. A dramatic effect upon the lithium motion and the microviscosity of the amorphous phase was noted upon the mixing of salts. It is proposed that some lithium ions are in environments of low symmetry, possibly of the ion-pair type, and do not contribute to the n.m.r. signal. The recrystallisation behaviour of the mixed-salt material was studied by the n.m.r. technique and an initial fast recrystallisation appears to be due to the formation of the high-melting temperature phase.

The dynamics of the crystallisation process in a mixed salt/polyethylene oxide (PEO) solid ionic conductor is investigated, using nuclear magnetic resonance techniques. The formation of the crystalline complex and the formation of the PEO crystals from 100% amorphous samples (obtained by a quenching technique) are observed, by 1H NMR, to occur with time constants sufficiently different to permit easy identification of the components of the inhomogeneous samples at equilibrium at 313 K. 19F NMR then shows in which component of the sample the anions reside. The evidence is that the anion/cation pairs of a particular salt do not in general reside in the same component of the samples.

The photo-oxidation of styrene type copolymers has been investigated using radiation with λ > 300 nm. At less than 1% oxidation, carbon dioxide and water were produced in significant quantities but at later stages O 2 uptake was predominant. The reaction was initiated by light of wavelength up to 330 nm and the rate of the early part was proportional to the light intensity. A three stage mechanism has been proposed for the reaction; an initiation phase, involving the production of hydroperoxides from charge transfer complexes between oxygen and phenyl units, is followed by the breakdown of the hydroperoxides to form ketonic groups, and the final and most important stage is the production of oxygen-consuming radicals by excited states of the ketones. A dark reaction proceeded at a rate of oxygen up-take comparable with that observed during the period of radiation.

Electrolyte a base d'un copolymere styrene-butadiene-styrene avec une courte chaine laterale polyoxyde d'ethylene et interaction avec le trifluoromethanesulfonate de lithium. Relation entre la concentration et la conductivite

Experimental techniques and theoretical analyses of thermogravimetry as applied to the thermal decomposition of polymers are reviewed. It is concluded that little useful mechanistic information can be derived simply by measuring weight loss during heating. Stability assessments can be based on apparent A and E values determined by isothermal analysis. However, such parameters will apply only within the temperature range defined by the conditions of data collection.

The conductance/temperature behaviour of poly(ethylene oxide)/LiClO4 electrolyte prepared under anhydrous conditions has been studied. Amorphous electrolyte samples have been crosslinked using γ-radiation from a Co-60 source. It is shown that light crosslinking cause a small reduction in the conductivity, probably due to restricted backbone segmental motion; however the tendency of electrolyte, treated in this way, to transform to a mixed crystalline/amorphous state of much lower conductivity, seems to have been comletely eliminated.

The effect of the mixing of lithium triflate and sodium iodide at high and equal concentrations in a polymer-based (poly(ethylene oxide)) ionic conductor are investigated. A variety of characterisation techniques, namely conductivity, X-ray diffraction, DSC and NMR, are employed. The salient observations involve enhanced conductivities, reduced microviscosity, greatly enhanced mobility of those lithium ions observed by NMR and a recurring absence of NMR observability of a substantial fraction of the cations. The data are interpreted as indicating that the effects of mixing of the salts are to enhance greatly the volume of available amorphous phase. Another feature of the interpretation is the inhomogeneous distribution of the various cations and anions around the different phases present in the materials.

In the photophysics of macromolecular systems, migration of singlet electronic energy has been accepted as a phenomenon which occurs for poly(vinyl arenes) both in solution and in the solid state. Experimental evidence, on which the postulated mechanism is based, is reviewed and many of the observations accounted for by proposing triplet energy migration which is a more likely process than migration involving the very short-lived singlet state.

It is found that oxygen accelerates the photodecomposition of poly(vinyl chloride) whereas hydrogen chloride inhibits it. It is postulated that O 2 quenches energy-rich polyenes and reacts in the singlet state ultimately yielding carbonyl functions which themselves absorb the radiation and speed up the photodecomposition. The HCl is thought to undergo addition to already formed polyenes thereby reducing the amount of light absorbed and consequently causing retardation.

The synthesis and some of the properties of a novel ion-conducting polymer are described. The polymer, based on a styrene-butadiene-styrene ABA triblock copolymer has pendant, short-chain poly(ethylene oxide) (PEO) grafted onto the B block. The concentration of PEO in the polymer can be controlled by varying either the number of pendant groups per molecule or the molecular weight of the PEO chain. The polymers were combined with LiCF 3 SO 3 to form ion-conducting phases. The conductivities of films of these materials were found to be sensitive to preparation technique, and especially to casting solvent. The best conductivities, typically 10 −5 S cm −1 at ambient temperatures, were obtained using solvents that were likely to induce microphase separation (with concomitant improvement in the mechanical properties of the system). The temperature dependence of the conductivity suggested that the materials were essentially amorphous over the range studied.

The kinetics of random and end-initiated depolymerization are examined taking into account distribution of molecular sizes. It is shown that for a sample undergoing random scission with complete unzipping the breadth of the distribution of molecular weights as measured by the ratio P w / P n has a marked effect on the relationships between sample weight, molecular weight, and time. Furthermore the molecular weight/conversion curves for this condition lie in the area of the graph which hitherto had been assumed to indicate end-initiated depolymerization uniquely. It is proposed that the order of the reaction with respect to weight of sample is a reliable guide to the mechanism of initiation. On the experimental side it is suggested that interpretation of thermogravimetric analysis data in depolymerization experiments must be made in light of the fact that the order of the reaction will alter once the molecular population changes due to loss of molecules, and since distribution of molecular weights has such a marked effect on randomly initiated reactions, this parameter should be measured in experimental investigations of depolymerization.

The products of the thermal decomposition of a series of copolymers of structure with n = 1, 3, 4, 5, 6, and 10 have been investigated. The volatile product consists largely of low molecular weight analogues of the parent polymer with α-methyl styrene as the major constituent of the volatile liquid fraction. Mechanisms are postulated to account for the formation of most of the volatile products; the importance of secondary chemical reactions is emphasized.

Cast poly(vinyl chloride) films have been irradiated by ultra-violet light at various intensities and temperatures under a nitrogen atmosphere. The dehydrochlorination reaction is shown to occur in two parts. During the first hour the reaction is dependent on intensity and temperature but later it is independent of these two parameters.

A survey is made of vinyl-type polymers in which there appear to be links more susceptible to scission (during thermal degradation) than the normal links. The presence of such links is indicated by an examination of the change in molecular weight during the course of the reaction. A theoretical expression is used which assumes that both normal, and weak link scission, are random processes. Apart from the polymers already known to have weak links, polystyrene, polyethylene, polymethylene, and polypropylene, it appears that poly(methyl methacrylate) also contains such links. It is suggested that an alternative explanation may account for the apparent presence of weak links in so many polymers. In einem Uberblick werden die Bindungen in Vinylpolymeren betrachtet, die wahrend eines thermischen Abbaus anscheinend eher spalten als gewohnliche Bindungen. Derartige Bindungen zeigen sich, indem man die Anderung des Molekulargewichts wahrend des Reaktionsverlaufs untersucht. Es wird eine theoretische Beziehung angewendet, nach welcher die Spaltung sowohl gewohnlicher als auch schwacher Bindungen statistisch verlaft. Neben den bekannten Polymeren mit schwachen Bindungen wie Polystyrol, Polyathylen, Polymethylen und Polypropylen scheint auch Polymethacrylsauremethylester derartige Bindungen zu enthalten. Es wird eine andere Erklarung dafur gegeben, das in so vielen Polymeren schwache Bindungen vorliegen sollen.

It is proposed that the adiabatic bulk modulus of a polymeric glass is determined by interchain forces which obey conventional intermolecular force relationships. Based on the Lennard-Jones expression for the intermolecular forces in liquids an equation is derived relating the bulk modulus and the volume of the polymer glass relative to its volume at the condition of zero expansion volume. The relationship deduced is tested on data available for poly(methyl methacrylate), polystyrene, polyethylene, and poly(vinyl chloride).

A survey is made of the experimental and theoretical studies of the thermal degradation of poly(methyl methacrylate). The mechanism proposed by GORDON is shown to be incorrect. At 300°C the reaction causing complete depolymerisation of the fraction of a polymer sample which is stable at 270°C. is initiated at random in the polymer molecules. It is shown that care must be taken when interpreting percentage molecular weight versus percentage degradation plots as a guide to mechanism of a depolymerisation reaction. Es wird ein Uberblick der experimentellen und theoretischen Untersuchung des thermischen Abbaus von Polymethacrylsauremethylester gegeben. Der von GORDON vorgeschlagene Mechanismus und die Kinetik treffen nicht zu. Die bei 300°C vollstandig verlaufende Depolymerisation einer bei 270°C bestandigen Polymerfraktion wird durch statistischen Angriff der polymeren Molekule ausgelost. Wenn man den Mechanismus einer Abbaureaktion erschliesen will, mus die Auswertung einer Beziehung Prozent des Molekulargewichts zu Prozent Abbau sorgfaltig erfolgen.

It is some 10 years or so since I first became involved in the question of the validity of non-isothermal rate equations [l] and still papers appear devoted to this subject 121. The specific objection to my proposals has been that conversion and time are not state functions, and therefore the use of partial derivatives in my original paper was incorrect. While the controversy was not totally resolved, it seemed. following a number of papers by Sest&k and co-workers [3,4], that the bulk of opinion was against my approach, although clear proof one way or the other was lacking. One piece of evidence of detail rather than of principle which is frequently quoted as demonstration of the validity of the single term rate expression is that shown in Fig. 9 of ref. 3, in which Holba and gest&k plot rate of reaction (as fractional conversion) vs. T according to the one term [eqn. (15) ref. 31 and the two term [eqn. (22), ref. 3) rate expressions_ The authors claim that the fair agreement between the one term theory and experimental plots, compared with their evaluation of the two term expression, constitutes good evidence for the validity of the one term rate expression. Using their two term expression they calculate that the maximum rate is almost an order of magnitude higher than that observed experimentally_ Their method of calculation is not clear but it is obvious that some serious error has been incorporated since (Y for all three curves goes to unity then the area under the curves for the plots of the two theoretical rates vs. temperature should be equal to each other and should be the same as that for the experimental plots. Indeed if the two term plot is scaled down to achieve this requirement then it appears that this function gives a closer fit to experimental observations than the single term analogue. I have now developed an alternative derivation based on accepted physicochemical principles which I believe resolves the problem of whether a one or two term rate expression is applicable to non-isothermal kinetics_ The basic premiseis that of the transition state theory which proposes. that the rate of a chemical reaction is proportional to the number of activated complexes, A*, which are themselves in equilibrium with reactant molecules A as shown by eqn. (1).

A model is proposed to account for the changes in the intensity of excimer to monomer fluorescence emission with varying molecular weight and copolymer composition. The theory is applied to published data for polystyrene homopolymers and copolymers, and satisfactorily accounts for the excimer;'monomer fluorescence ratio without involving the concept of energy migration.

The appropriate statement of the stationary-state hypothesis in bulk polymer degradation reactions is examined. It is concluded that the kinetics of those depolymerization reactions which are not first-order with respect to the weight of the sample cannot be analysed on the premise that the stationary-state hypothesis is applicable.

The major techniques of thermal analysis can readily be grouped into three headings, differential scanning calorimetry, DSC, differential thermal analysis, DTA, and thermogravimetry, TG. The latter technique is used widely as a means for assessing the thermal stability of polymeric materials and, as such, it can provide valuable technical information. It must be borne in mind that the conclusions drawn with regard to stability are only relevant within the context of loss-of-weight of the sample. There are reactions which can take place on heating a polymer and which alter drastically the physical properties of the material without an observed change in weight. The side chain condensation of polyacrylonitrile provides a good illustration of this type of reaction.

The life-time of phosphorescence emission from triphenylene and coronene suspended in a range of styrene/methyl methacrylate copolymers has been measured at 77 K. It has been concluded that the polymer matrix quenches the triplet state of the polycyclic aromatics, presumably by an energy transfer mechanism.

The optical anisotropy of excimer emission from polystyrene dissolved in dichloromethane is found to vary with concentration and molecular weight. It is concluded that the time constant for rotation of the dimeric structure increases with increasing both concentration and molecular weight. It is proposed that intermolecular interactions cause this, and such interactions occur well below the concentration corresponding to overlap of macromolecules.

Polarization of fluorescent emission of excimer structures for polystyrene and poly (α-methyl styrene) has been examined in cyclohexane solution. No depolarization was observed resulting in the conclusion that energy migration does not take place under the experimental conditions studied.