Synthesis of monodisperse polymeric microspheres including polyimide prepolymer by using SPG emulsification technique

An occlusion of a functional material, polyimide prepolymer (PIP), into uni form polymeric microspheres was attempted in order to demonstrate the versa tility of the SPG (Shirasu porous glass) membrane emulsification technique. An oil phase consisting of hydrophobic monomers (styrene and acrylates wit h a longer side chain) and, although not necessarily, a water-insoluble rea gent (lauryl alcohol) dissolved PIP up to 50 wt.%, and also an initiator (A DVN). An aqueous phase contained polyvinyl alcohol (PVA) and a small amount of sodium lauryl sulfate (SLS) as a stabilizing pair. The former was perme ated through a SPG membrane, and uniform droplets were suspended in the lat ter. The seed droplets were swollen with the hydrophilic components, MMA an d EGDMA, with a selective addition of isoamyl acetate, hexanol or octanol. After the swelling, an additional amount of the stabilizer solution was add ed. Polymerization was carried out at 343 K for 24 h. Uniform polymeric sph eres, the coefficient of variation approximately 10% and occluding a maximu m 28.4 wt.% of PIP were obtained. The entrapment of PIP was improved when t he matrix polymer chains were crosslinked with EGDMA (but not with DVB), an d an employment of the acrylates with a longer side chain, implying that th e presence of ester groups are favored for a stable occlusion. A co-monomer system composed of MMA, 2-ethylhexyl acrylate and butyl acrylate plus octy l alcohol was able to occlude almost 100% of PIP in a stable condition with out the presence of EGDMA. (C) 1999 Elsevier Science B.V. All rights reserv ed.