Steric stabilization by grafting and copolymerization of water‐soluble oligomers and polymers

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Abstract
Different types of nonionic, water‐soluble polymers and macromonomers are investigated as emulsion stabilizers in the batch emulsion polymerization of styrene. A power law dependence of the rate of polymerization vs. stabilizer concentration is observed, in formal accordance to Smith‐Ewart kinetics. For water‐soluble polymers, exponents in the range of 0,6 are found which are close to that of the reference anionic surfactant (0,67). The differences are mainly attributed to the larger initial particle size which is accompanied by secondary agglomeration during polymerization. Several reasons for this agglomeration are discussed which have their origin in the solution and adsorption properties of the water‐soluble polymers. Compared to the non‐functional polymers some macromonomers show a similar kinetic behavior with exponents in the range of 0,4 to 0,5, while others give very small values. These differences strongly depend on the molecular structure of the macromonomers. They are in particular attributed to enhanced homopolymerization as well as solubility in monomer and polymer. No secondary agglomeration takes place when using macromonomers as emulsion stabilizers. This is due to the enhanced colloidal stability because of the defined bonding of the macromonomers to the latex particle surface as compared to the more random grafting of the non‐functional water‐soluble polymers.

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