A study of poly[3-(dimethoxymethylsilyl)-1-propanethiol] dispersion stability: from emulsions to latexes

Abstract

In this work the polymerisation of 3-(dimethoxymethylsilyl)-1-propanethiol (DMST) is investigated in aqueous ethanol solution under alkaline conditions. During heating droplets containing cyclic DMST and linear poly(DMST) are formed. The droplet size increases during synthesis to above 5 µm which is accompanied by sedimentation of a gel phase. The data presented support the view that this is due to flocculation. During this process cyclic DMST undergoes ring opening polymerisation and increases the proportion of linear species present. The dispersion stability was improved by adding methoxy-poly(ethyleneglycol) methacrylate (MPEGMa, Mn = 1100 g mol⁻¹) during the early stages of poly(DMST) particle growth. This resulted in grafting of MPEGMa to the particle surface by a Michael addition. The grafted layer thickness was ca. 10 nm and conferred steric stabilisation to the dispersion. The final particle size was ca. 2.8 µm. The particles at the lower end of the particle size distribution exhibited hexagonal close packing when observed by scanning electron microscopy.