From Polymers to Plastics by A. K. van der Vegt

By A. K. van der Vegt

Therapy of homes and constitution of polymers and behavior of plastics fabrics.

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Well, it is easy to understand that various polymer properties are influenced by the molar mass. Moreover, it appears that different physical properties of polymers are controlled by different types of average molar mass. A few examples: Molecular composition 31 — – The number average, Mn , is proportional to the mass of one gramme of the polymer divided by the number of chains. It is, therefore, a function of the number of chains, and thus of the number of chain ends (apart from branching). Now suppose that a crack with a sharp tip propagates through a piece of the polymer, then this propagation is easier as less chains have to be broken, and it meets more chain ends on its way.

First the smaller molecules are taken away from the column, later on the bigger ones. g. by a viscosity measurement). g. 20) of different fractions. This Baker-Williams method is very time-consuming: fractionation and characterization of a sample takes, in total, about a week. A more modern method to determine the MMD is GPC, gel permeation chromatography, also named size-exclusion chromatography, SEC. A polymer solution is passed over a column with a porous structure. The residence time of the chains on the column depends on the diameter of the coiled chain: smaller chains can migrate through more pores (they can also enter into the smaller ones), and it takes a longer time for them to pass along the column.

E is related to ν, M and Mc according to Mc νe = ν·[1 – 2· M ] since the chain is divided into n = M/M c parts, two of which are always loose, so that the effective fraction is (n – 2)/n = 1 – 2/n. In our case νe = 8(1 – 2 × 250/1000) = 4. In this example only one half of the chain parts are effectively contributing to the network properties; the remaining part, the loose ends, are not being deformed when the material is strained. 1) and from swelling in solvents. In most cases, cross-linking is effected by the formation of chemical bonds between the chains; the network is then stable, such as with: – sulphur bridges with rubbers, – polystyrene chains with unsaturated polyesters, – bivalent with three- (or more-)valent reacting components, – cross-linking by irradiation; via radical formation a chemical link between chains is formed.

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