Abstract
AbstractDuring the emulsion polymerization of ethylene the solubility of the monomer at 85°C and 4500 psig is 0.3–0.6 mol/1 in the aqueous phase and about 5 mol/1 in the monomer‐polymer particle. Hence, ethylene, like vinyl acetate, can be considered a water‐soluble monomer. The rate of polymer formation is proportional to the square root of the initiator concentration. The polymers contain a large amount of low molecular weight polymer that contributes to their characteristic lack of elongation at break. They also contain emulsifier covalently bound in the polymer by a chain‐transfer reaction. Because chain transfer occurs with emulsifier adsorbed on the particle surface and retards the rate of polymer formation, the molecular weight of the polymer is proportional to the particle diameter and the rate of polymer formation is inversely proportional to the emulsifier concentration. Based on similarities in dependence of density and branching on temperature, the propagation step in emulsion polymerization resembles that in the high pressure synthesis of polyethylene. In the absence of chain transfer, however, the structure of emulsion polyethylene becomes complex.
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