Synthesis And Characterization Of Monodisperse Polyimide Particles

Polyimide spherical particles have some unique properties such as outstading surface performance, large ratio of surface to volume, intense adsorbability, that because of their special structure and size. and it also has excellent thermal stability and solventresistance,along with good mechanical and electrical properties. it will have potential applications of the microsphere in sophisticated technique such as medical treatment, medicine biochemistry, isolation/adsorption materials, catalyst carrier, coating,bioengineering, information technology.In this article, a kind of poly(amic acid)(PAA) has been synthesized from Pyromellitic dianhydride (PMDA) and 4,4'-diamino diphenyl (ODA) with the magnetic stirring. Subsequently , polyimide particles formed by via of imidezation. polyimide polymer particles were prepared by using precipitation polycondensation and suspension polycondensation, respectively. The mixture of THF/MeOH is a new solvent in precipitation polycondensation. and the suspension polycondensation is different from the normal suspension method. By changing the recipes of solvent and reaction condition,the effects on size,dispersion and morphology were investigated.PI particles can be obtained from PAA after two-steps imidization -chemical imidization and thermal imidization. PI particle can be obtained finally.(1) poly(amic acid)(PAA) as a precursor polymer was fabricated by Pyromellitic dianhydride (PMDA),4,4'-diamino diphenyl (ODA) in the mixture of THF and MeOH, polyimide (PI) fine particles were obtained through the"two-steps imidization",chemical imidization and thermal imidization of PAA solution. The effect of morphology ,particle size and the dispersion of PI particles was studied when different solvent was used.SEM showed that PI particles obtained in the solvent of the mixture (THF/MeOH=7:3) and the particle size range is 5 to 10μm.The peak viscosity of PAA appeared after 4 h reaction. Infrared spectroscopy indicated that PI particles yielded after Two-steps Imidization. Thermogravimetric analysis test indicated that PI particles T5d , Td1 0 is 530℃,560℃, respectively.(2) Cyclohexane is a key factor in suspension polymerization system, and have an important effect on the size of PI particles.The properties of particles are characterized by SEM , IR spectro scopy and XRD. As a result , the diameter of polyimide particles decreased with increasing the Cyclohexane contens and thestirring speed. the polymer microespheres with the size f rom 0. 5μm to 15μm ,There is no crystalline structure in the polyimide particles.