On the Kinetics of Inverse Emulsion Polymerization of Acrylamide

Abstract

The inverse emulsion polymerization of acrylamide (AAm) initiated by a water-soluble initiator (ammonium peroxodisulfate, APS) was investigated. The rate of inverse emulsion polymerization increased with both increasing initiator and emulsifier concentrations. The molecular weight of polyacrylamide decreased with increasing the initiator concentration and slightly rose with increasing the emulsifier concentration. With increasing APS concentration the curves are broader. This indicates widening of molecular weight distribution. The decrease in M¯ _w with increasing APS concentration results from the increased termination of growing radicals mainly by primary or oligomeric radicals. The number of radicals per particle was inversely proportional to the APS concentration. The increased deactivation of primary and monomeric radicals decreased their desorption rate and re-entry rates as well. The desorption rate of radicals was interpreted using three models: the Nomura model (N_model, k′ _{des, N}), the Gilbert model (G_model, k′ _{des, G}) and the Ugelstadt model (T_model, k′ _{des, T}). The desorption rate constant (k′ _des) for the different models differs by up to two orders of magnitude. The value of k _des increases in the following order: N_model < G_model < T_model. The radical entry rate decreases with rising emulsifier concentration and increases with rising initiator concentration.

Keywords:

• ACRYLAMIDE
• INVERSE EMULSION POLYMERIZATION
• POLYMERIZATION RATE
• DESORPTION OF RADICALS
• POLYMER MOLECULAR WEIGHTS