Fundamentals of polymer chemistry / Henry Warson / n.d.  

Titre : Fundamentals of polymer chemistry Type de document : document électronique Auteurs : Henry Warson, Auteur Année de publication : n.d. Importance : 48 p. Présentation : ill. Format : 30 cm Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Polymères Index. décimale : 668.9 Polymères Résumé : The differences between the properties of crystalline organic materials of low molecular weight and the more indefinable class of materials referred to by Graham in 1861 as ‘colloids’ has long engaged the attention of chemists. This class includes natural substances such as gum acacia, which in solution are unable to pass through a semi-permeable membrane. Rubber is also included among this class of material. The idea that the distinguishing feature of colloids was that they had a much higher molecular weight than crystalline substances came fairly slowly. Until the work of Raoult, who developed the cryoscopic method of estimating molecular weight, and Van’t Hoff, who enunciated the solution laws, it was difficult to estimate even approximately the polymeric state of materials. It also seems that in the nineteenth century there was little idea that a colloid could consist, not of a product of fixed molecular weight, but of molecules of a broad band of molecular weights with essentially the same repeat units in each. Vague ideas of partial valence unfortunately derived from inorganic chemistry and a preoccupation with the idea of ring formation persisted until after 1920. In addition chemists did not realise that a process such as ozonisation virtually destroyed a polymer as such, and the molecular weight of the ozonide, for example of rubber, had no bearing on the original molecular weight. The theory that polymers are built up of chain formulae was vigorously advocated by Staudinger from 1920 onwards. He extended this in 1929 to the idea of a three-dimensional network copolymer to account for the insolubility and infusibility of many synthetic polymers, for by that time technology had by far outstripped theory. Continuing the historical outline, mention must be made of Carothers, who from 1929 began a classical series of experiments which indicated that polymers of definite structure could be obtained by the use of classical organic chemical reactions, the properties of the polymer being controlled by the starting compounds [2]. Whilst this was based on research in condensation compounds (see Section 1.2) the principles hold good for addition polymers. The last four decades have seen major advances in the characterisation of polymers. Apart from increased sophistication in methods of measuring molecular weight, such as the cryoscopic and vapour pressure methods, almost the whole range of the spectrum has been called into service to elucidate polymer structure. Ultraviolet and visible spectroscopy, infrared spectroscopy, Raman and emission spectroscopy, photon correlation spectroscopy, nuclear magnetic resonance and electron spin resonance all play a part in our understanding of the structure of polymers ; X-ray diffraction and small-angle X-ray scattering have been used with solid polymers. Thermal behaviour in its various aspects, including differential thermal analysis and high-temperature pyrolysis followed by gas–liquid chromatography, has also been of considerable value. Other separation methods include size exclusion and hydrodynamic chromatography. Electron microscopy is of special interest with particles formed in emulsion polymerisation. Thermal and gravimetric analysis give useful information in many cases. There are a number of standard works that can be consulted. En ligne : http://media.wiley.com/product_data/excerpt/80/04719526/0471952680.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=29887

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Measuring in microns / Henry Warson in POLYMERS PAINT COLOUR JOURNAL - PPCJ, Vol. 192, N° 4451 (04/2002)

[article]  inPOLYMERS PAINT COLOUR JOURNAL - PPCJ > Vol. 192, N° 4451 (04/2002) . - p. 17-19 Titre : Measuring in microns Type de document : texte imprimé Auteurs : Henry Warson, Auteur Année de publication : 2002 Article en page(s) : p. 17-19 Langues : Anglais (eng) Catégories : Latex Mesure Mesure -- Instruments Taille des particules Index. décimale : 667.9 Revêtements et enduits Résumé : The author details just a few of the methods and instruments available that are able to measure the size of fine particles down to 0.003 micrometers in diameter. The methods of measuring fine particle sizes have seen major developments in the past few decades. This applies to fine solids, but especially to latex particules. The oldest method for separating solid particles by size was the use of a sieve. Later, a range of sieves with different meshes was used. Woven sieves are available for measuring sizes of particles from several millimeters to 20 micrometers, although some care is needed in the latter case to ensure that the sieve does not become distortes. Shape has a strong influence on particule size by sieving. Originally, the only method of measuring the size of latex particles was by direct microscopic observation, which could give a maximum magnification of about 400. The phase microscope with oil immersion increases magnification to a maximum of about 600. The latex is diluted at least 10 times before a drop is placed on a slide and a cover glass is pressed over it. The assumption here is that particles in latex are essentially spherical, but this is noy always true. Simple observations can show whether particles in any latex are unisized or have a variety of sizes and shapes. In dealing with solids, size and shape have more significances. The minimum size which can be observed directly is about 0.4 micrometers. Note de contenu : - Modern methods - Electrode method - Light scattering - Photo correlation spectroscopy - Fine solids measurement - Turbimetry - Disc centrifuge - FIGURES : 1a. Flow schematics of Horiba system - 1b. Operation of Horiba system - 2. Accusizer 780 particle sizing system - 3. Brookhaven instrument, showing the effects of spinning - Equation 1. The stokes equation, which relates the sedimentation of particles to size and viscosity Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=28092 [article]

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