Compression, supramolecular organization and free radical polymerization of ethylene gas

Abstract

© 2019, Iran Polymer and Petrochemical Institute. All rights reserved. At low pressure, ethylene gas consists of single translating and rotating molecules and behaves as an ideal gas. With decrease of free volume by compression, various rotating supramolecular particles are formed, which require less space for the movement: molecular pairs, bimolecules and oligomolecules. The appearance of a new kind of particles is manifested as a phase transition of the second or third order. An ideal gas consists of single translating and rotating molecules. α phase consists of rotating single molecules and rotating molecular pairs and it exists when the volume V is reduced to V c <V<2V c . (V c is critical volume). β phase consists of molecular pairs and bimolecules and it exists when V<V c and S>S. c (S c is critical entropy). γ phase and liquid ethylene consist of bimolecules and oligomolecules and they exist when S<S c . The main goal of this article is to publish how we developed that model and what were thermodynamical, physical and chemical evidences which confirmed its validity. Instead of the classical theory of radical polymerization, we applied Kargin and Kabanov theory of polymerization of organized monomer to interpret high pressure free radical polymerization of ethylene. The arrangement of monomer molecules in individual supramolecular particles and the supramolecular organization of whole system have decisive effects on the mechanism and kinetics of polymerization and on the formation of polymer structure and properties, i.e. molecular mass and its distribution, branching, density, etc. There is isentropic rule: the same structures and properties are obtained for polyethylene if the entropy of ethylene under polymerization conditions is the same, regardless the differences in other polymerization conditions, i.e. reactor type, pressure, temperature and method of initiation. Mathematical models of the effect of ethylene entropy on polyethylene structure and density enable practical design of polyethylene with desired characteristics. Finally, it is mentioned that we expanded the model of ethylene to other gases and liquids as well as to other polymerization cases, including liquid monomers and olefins polymerization by Ziegler-Natta, metallocene and Phillips catalysts.