In situ stabilizer formation from methacrylic acid macromonomers in emulsion polymerization

Oligomers of methacrylic acid containing a propenyl ω-endgroup (i.e. MAA-macromonomers) were synthesized by cobalt-mediated catalytic chain transfer polymerization and used as precursors to stabilizers in emulsion polymerization. It was found that only in those polymerizations in which these precursors were sufficiently quickly converted into amphiphilic molecules, via a type of polymerization induced self-assembly (PISA) mechanism, stable emulsion polymerization could be carried out. This process was too slow in the emulsion polymerization of methyl methacrylate (MMA) and in order to obtain stable latexes, the addition of a conventional surfactant (sodium dodecyl sulphate, SDS) was necessary. In the emulsion polymerization of butyl acrylate, however, reactions with the macromonomers were faster and because of the more hydrophobic nature of BA (as compared to MMA), stabilizers were sufficiently quickly formed in situ and stable latexes were produced without the need for additional SDS. Also the emulsion polymerization of butyl methacrylate (BMA), which reacts via the same “sulfur-free RAFT” mechanism as MMA, could be carried out in the absence of SDS because of the greater hydrophobicity of the monomer. Copolymerizations of MMA with >30% of BA or 85% BMA also resulted in stable latexes without the addition of SDS. The synthesized macromonomers and in situ formed copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy and MALDI-ToF MS.