MECHANISM, KINETICS AND MODELING OF INVERSE-MICROSUSPENSION POLYMERIZATION .2. COPOLYMERIZATION OF ACRYLAMIDE WITH QUATERNARY AMMONIUM CATIONIC MONOMERS

A mechanism has been developed for the inverse-microsuspension polymerization of acrylic water-soluble monomers. This includes the influence of ionogenic monomers and polyelectrolytes, and has been applied to the copolymerization of acrylamide with quaternary ammonium species. A multistage experimental investigation has also been conducted so that phenomena unique to the kinetic model can be isolated, and independent parameter estimates generated. This included: homopolymerizations in aqueous solution and inverse microsuspension, to measure the rate parameter k(p)/k(t)1/2 and decouple it from the initiation efficiency; monomer partitioning measurements to distinguish the rate of macroradical chain addition in the aqueous and organic phases; and copolymerization in inverse microsuspension. The reaction system consisted of the cationic monomers dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, Isopar-K as the organic phase, and fatty acid esters of sorbitan as steric stabilizers. Polymerizations were performed between 40 and 60-degrees-C and were chemically initiated with oil-soluble (azobisisobutyronitrile) and water-soluble (potassium persulphate) species. The experiments have confirmed the three main postulates of the reaction mechanism: specifically, that nucleation and polymerization occur within the monomer droplets; heterophase diffusion-limited oligoradical precipitation is the predominant initiation reaction; and unimolecular termination with interfacial species is competitive with the bimolecular process. Further, propagation and termination were not found to be influenced by the nature of the polymerization system, proceeding at equal rates in solution and inverse microsuspension. The kinetic model is therefore found to be in excellent agreement with experimental polymerization rate, copolymer composition and particle size data.