Chap._100011 - destroy the colloidal properties of the...

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* Average molecular weight Number average molecular weight (Mn) Weight average molecular weight (Mw) measured by colligative properties measured by light-scattering (such as freezing point depression) or osmotic pressure * Some historical Aspects 1850s: The existence of atoms and molecules was accepted. 1861: Graham found that solutions of such natural materials as gelatin and glue (from nature) diffused through a parchment membrane at a very slow rate. Materials of this kind were called colloids (Greek: kolia-glue). In contrast, solutions of materials like sugar and salts diffused readily early 1900s: Some molecules, such as nature rubber were then supposed to aggregate “colloidal particles” by virtue of secondary valency forces (physical interactions) arising from the presence of double bonds 1920s: Staudinger in Germany proposed the long chain structure-macromolecule, which is accepted today. He showed that, contrary to then current expectations, chemical modification does not
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Unformatted text preview: destroy the colloidal properties of the organic materials. Additional support for the existence of macromolecules came with the development of methods of molecular weight determination. 1930: Carothers in the USA synthesize polymers of definite structure through the use of established reactions of organic chemistry and the elucidation of the relationship between structure and properties of polymers. These researches were brilliantly successful and finally dispelled the mysticism surrounding this field of chemistry. One outstanding result of Carothers' work was the commercial development of nylon. Nylon stockings came on the market in 1940, when polymers, in terms of popular acceptance, might be said to have arrived. The theoretical, practical and economic foundations had been laid and since this date progress has been phenomena....
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