Chemical analysis has shown that the important structural components of the body are high polymers, so I intend to consider their formation from the point of view of polymer chemistry. These compounds are distinguished by being of high molecular weight and formed from a limited number of structural components, which are joined together either by direct addition, or by the elimination of water, as in the case of the formation of proteins from amino-acids and polysaccharides from sugars. It is best to consider first the synthetic polymers (1), since the mechanism of their formation is known in the greatest detail, to find the type of factors which are of importance. Polyethylene is the simplest polymer, but there are variations in its physical properties according to the method of manufacture. The texture and softening point can show considerable differences with chain branching. The nylons show variations in extensibility and dye uptake, caused by small differences in physical conditions of production; but they also show variations in these and other properties, such as solubility, according to the identity and proportion of their components. These and the majority of the commercial polymers are first polymerized and then processed. The synthetic polymer, methacrylate, is polymerized in the form in which it is to be used. With a mixture containing methyl methacrylate shrinkage occurs and a badly shaped object results; if butyl or isobutyl methacrylate is chosen instead, one should get the shape of the mould reproduced, in the presence of a suitable catalyst.
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