Preparation Of Polyimide Microspheres In Nonaqueous Inverse Emulsion

The routes for synthesis of microspheres include emulsion polymerization suspension polymerization dispersion polymerization and precipitation polymerization. Due to the existence of aqueous, emulsion polymerization was not suitable to prepare polyimide microspheres. According to other literatures, the essence of suspension polymerization dispersion polymerization and precipitation polymerization was to precipitate polyimide microspheres using the difference of solubility Parameter. In the process, it would lead polyimide microspheres to adhesion and width size distribution.To overcome the shortcomings of these methods mentioned above, the non-aqueous inverse emulsion was used in the method for the synthesis of PI microspheres. The non-aqueous inverse emulsion was compounded with N,N-dimethyl formamide / (pluronic-F127, dodecylbenzenesulf) / liquid paraffin, in which the polyamic acid was synthesized with monomers of pyromellitic dianhydride and 4,4′-diamido diphenyl aether. Then, to avoide the adgesion between the microspheres and the negative impact of hydrolysis on the material properties, the polyimide particles were precipitated through the chemical imidization using the acetic anhydride/pyridine mixture as dehydrating agent. Ultimately, polyimide particles were completely imidized via thermal imidization.The method was suitable for praperetion of polyimide microspheresin, because of the absence of aqueous. In addition, the polyimide particles were good dispersity, spherical and high thermal stability.The main conclusion of this paper were as following:(1) The preparation of nonaqueous inverse emulsionIn the nonaqueous inverse emulsion system, the influence of the feeding sequence, the chemical imidization time, solid content, thermal imidization temperature was investigated. The product was characterized by FITR, SEM, TG. The results showed that polyimide microspheres with good dispersity and spherical morphology could be obtained when the chemical imidization time is 2h, the solid content was 20% and the thermal imidization temperature was less than 330℃. The average particle diameter was about 10μm.(2) The synthesis of polyimide microspheresThe factors which impacted the stability of nonaqueoue inverse emulsion were investigated, namely: the volume ratio of the two phase, the content of the emulsifiers, the compound ratio of the emulsifiers. The nonaqueoue inverse emulsion was characterized by centrifugation, stationarily, and the polarized microscope. The results showed that the non-aqueous inverse emulsion was optimal when the volume ratio of N,N-dimethyl formamide/liquid paraffin was 1:4, the mass ratio of pluronic-F127/dodecylbenzenesulf was 3:2, and the content of emulsifiers was 9 wt%. Under these conditions, the nonaqueous inverse emulsion had not appeared strstification, phase-inversion and flocculation when it was centrifuged at 3000r/min for 15min and standed for 48h at room temperature.(3) The synthesis of porous polyimide microspheresAccording to the mechanism of porous microspheres, LiCl,CS2,C6H5CH3 were used as porogen, and added in different stages in the reaction. The impact of the content of porogen was investigated. The product was characterized by SEM, TG. The results indicated that the spherical was destroyed when the porogens were LiCl and C6H5CH3. In the end, the porous polyimide microspheres was obtained by using CS2 as porogen, meanwhile the ratio of CS2 to N,N-dimethyl formamide was 0.06: 1.