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

Abstract

An occlusion of a functional material, polyimide prepolymer (PIP), into uniform polymeric microspheres was attempted in order to demonstrate the versatility of the SPG (Shirasu porous glass) membrane emulsification technique. An oil phase consisting of hydrophobic monomers (styrene and acrylates with a longer side chain) and, although not necessarily, a water-insoluble reagent (lauryl alcohol) dissolved PIP up to 50 wt.%, and also an initiator (ADVN). An aqueous phase contained polyvinyl alcohol (PVA) and a small amount of sodium lauryl sulfate (SLS) as a stabilizing pair. The former was permeated through a SPG membrane, and uniform droplets were suspended in the latter. The seed droplets were swollen with the hydrophilic components, MMA and EGDMA, with a selective addition of isoamyl acetate, hexanol or octanol. After the swelling, an additional amount of the stabilizer solution was added. Polymerization was carried out at 343 K for 24 h. Uniform polymeric spheres, the coefficient of variation approximately 10% and occluding a maximum 28.4 wt.% of PIP were obtained. The entrapment of PIP was improved when the matrix polymer chains were crosslinked with EGDMA (but not with DVB), and an employment of the acrylates with a longer side chain, implying that the presence of ester groups are favored for a stable occlusion. A co-monomer system composed of MMA, 2-ethylhexyl acrylate and butyl acrylate plus octyl alcohol was able to occlude almost 100% of PIP in a stable condition without the presence of EGDMA.