Polymerization in supercritical fluids

Abstract

The chemical industry has become increasingly aware of environmental concerns over the use of volatile and hazardous organic solvents to synthesize commercial polymers. Attractive properties of supercritical fluids make them a potential alternative solvent in polymerization reactions. The present study deals with the kinetics of free radical polymerization of styrene, methyl methacrylate, butyl acrylate, and vinyl acetate in three supercritical fluids: carbon dioxide, methane, ethane, and in THF. The variation of molecular weight with initiator concentration was studied for the synthesis of all the polymers in different supercritical fluids. Experiments in supercritical fluids were carried out in a batch tubular reactor under high pressure, and reactions using THF as a solvent were also performed. In both cases, the number-average molecular weight of the polymer product was determined by gel permeation chromatography (GPC). Key observations:

The reaction rate in supercritical fluid is enhanced compared to the reaction rate in THF due to rapid mass transfer. The rate coefficients were determined, and the activation energies were calculated from the temperature dependence of the rate coefficient. The activation energies were in the range of 20.6 to 25.4 kcal/mol for the polymerization.