The Molecular Weight Distribution of Polymer Samples.

• Autores: Arturo Horta Zubiaga, Alejandra Pastoriza Martínez
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 84, Nº 7, 2007, págs. 1217-1221
• Idioma: inglés
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• Resumen

  • Introductory polymer courses and textbooks discuss the statistical distribution of chain lengths or molecular weight that exists in polymers and connect the averages and breadth of such distribution with the mechanism of the polymerization, for example, with the degree of advancement or stoichiometry in step-growth polymerization or with the existence of transferences or with the type of termination in chain addition polymerization. To determine averages and breadth of the distribution, the polymer has to be separated from the reaction medium and converted into a "sample". In this process, the shorter chains, which are most soluble, may be lost with the result that the sample is not identical to the original polymer. A student exercise is proposed and developed, in which we calculate the difference between "sample" and original polymer. We use standard material given in the introductory courses or textbooks such that the calculation can be performed easily by the students. The results are discussed to ascertain whether the different distribution of the sample may alter the interpretation of the mechanism by which the original polymer was obtained.