Abstract
AT the Friday evening discourse at the Royal Institution on April 23, Prof. H. Mark discussed “The Synthesis of Large Molecules”. In Nature, all organized objects consist of large molecules. The great importance of the natural highly polymerized substances has led to the conclusion that very valuable mechanical and physiological behaviour is associated with these macro-molecules. Therefore the industries concerned with synthetic rubber, artificial silk and synthetic resins have worked out a number of synthetic high polymers, which are, in fact, of great use in making insulators, fibres and solid materials of high resistance and valuable properties. It appears that the kinetics of polymerization reactions is very complicated, but one can already distinguish three main processes which play an important role in every polymerization reaction. First a nucleus of high reactivity must be built. This can be done by a thermal collision of high energy, or photochemically, or by means of a catalytic agent. The production of these nuclei requires a high activation energy, and is therefore rather slow. The nuclei react quickly with the molecules of the mono-meric substance and grow with rather high velocity step wise to a chain. The activation energy of the growing reaction is low (about 5,000 cal./mol.) and therefore the probability of the growth is large. The chains would grow infinitely if there were not break-up reactions of different kinds. There is the possibility that the growing of the chains may be ended by lack of monomeric substance; it is possible that the decreasing steric factor of the association reaction may diminish the velocity of chain growth to a very low rate, and one must consider that different side-reactions may break up the chains suddenly. In the case of styrene, we have succeeded in distinguishing these three different stages and developing a reaction mechanism which seems to be in fair agreement with the experimental data.
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Synthesis of Large Molecules. Nature 139, 749–750 (1937). https://doi.org/10.1038/139749d0
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DOI: https://doi.org/10.1038/139749d0