Fabrication of polyimide microspheres with high precursor polymer concentration

Polyimide (PI) microspheres with high precursor polymer concentration were successfully prepared using non-aqueous reverse emulsion polymerisation. The emulsion was composed of N, N-dimethyl formamide and liquid paraffin, in which Span85 was used as surfactant. The effect of Span85 concentration on the resulting PI product has been investigated. The results indicated that with the increase in Span85 concentration, the average diameter declined, and the size distribution became narrow. When the concentration of surfactant Span85 was around 0.15 w/w, a yellow-to-brown-coloured powder of PI microfine spheres was obtained, with an average particle size of 25.6 m. As an emulsifier and a chain termination agent, surfactant Span85 chemically bonded to the growing polymer chains, and not only formed stable non-aqueous inverse emulsion but also increased precursor polymer concentration.