Synthesis and Characterization of Polyol Poly-12-Hydroxy Stearic Acid: Applications in Preparing Environmentally Friendly Overbased Calcium Oleate Detergent

From near hard spheres to colloidal surfboards

This work revisits the synthesis of the colloidal particles most commonly used for making model near hard suspensions or as building blocks of model colloidal gels, i.e. sterically stabilised poly(methyl methacrylate) (PMMA) particles. The synthesis of these particles is notoriously hard to control and generally the problems are ascribed to the difficulty in synthesising the graft stabiliser (PMMA-g-PHSA). In the present work, it is shown that for improving the reliability of the synthesis as a whole, control over the polycondensation of the 12-polyhydroxystearic acid is the key. By changing the catalyst and performing the polycondensation in the melt, the chain length of the 12-polyhydroxystearic acid is better controlled, as confirmed by ¹H-NMR spectroscopy. Control over the graft copolymer now enables us to make small variations of near hard sphere colloids, for example spherical PMMA particles with essentially the same core size and different stabilising layer thicknesses can now be readily produced, imparting controlled particle softness. The PMMA spheres can be further employed to create, in gram scale quantities, colloidal building blocks having geometrical and/or chemical anisotropy by using a range of mechanical deformation methods. The versatility of the latter methods is demonstrated for polystyrene latex particles as well.

Revisiting the synthesis of a well-known comb-graft copolymer stabilizer and its application to the dispersion polymerization of poly(methyl methacrylate) in organic media

Polymeric stabilizers are an essential ingredient for the dispersion polymerization of poly(methyl methacrylate) (PMMA) in nonpolar media. In this contribution, we focus on the synthesis of an amphipathic copolymer consisting of pendant poly(12-hydroxystearic acid) (PHS) chains grafted to an insoluble PMMA backbone. This type of steric stabilizer is well established and capable of producing spherically shaped, monodisperse PMMA colloids. Unfortunately, the comb-graft copolymer is not available commercially; furthermore, the multistep synthesis of the desired stabilizer has proven challenging to reproduce. We discuss the practical matter of preparing PHS-graft-PMMA, and report specific techniques developed over several years in our lab. Gel permeation chromatography, mass spectroscopy, and end group analysis of the stabilizer and the precursor macromonomer reveal important, previously unreported details about the chemical synthesis. Our protocol is reproducible and resulted in the production of low polydispersity PMMA particles.