Nitroxide-mediated microemulsion polymerization of n-butyl acrylate: decoupling of target molecular weight and particle size

Abstract

The independent control of particle size and molecular weight is a highly desirable yet challenging objective to achieve in SG1-mediated living radical emulsion polymerizations. For example, to preserve colloidal stability, reduction in particle size typically necessitates making higher molecular weight chains, severely constricting the usefulness of the process. The strong inverse correlation between target molecular weight and particle size has been successfully decoupled to a significant extent in nitroxide-mediated microemulsion polymerization of n-butyl acrylate using a two-stage differential monomer addition technique. These microemulsion polymerizations were carried out at 120 °C using SG1-based alkoxyamine BlocBuilder® MA and the anionic surfactant Dowfax™ 8390 at low surfactant-to-monomer ratios (0.2 : 1 to 0.5 : 1 w/w) and a solids content of 20 wt%. The nanolatexes were colloidally stable and the polymerizations showed living and controlled behaviour. The mean particle diameters obtained ranged from 20–100 nm, although the focus was on particles in the 20–50 nm range, for target molecular weights from 20 000–80 000 g mol⁻¹. These results show that changing the surfactant-to-monomer ratio, the BlocBuilder® MA-to-buffer ratio, the initial monomer content in the seed stage, and surfactant feed rates can allow both molecular weight and particle size to be targeted independently in nitroxide-mediated microemulsion polymerization.