Preparation Of Polyimide Microspheres By Prfcipitation Polymerzation

Polyimide (PI) microspheres have excellent performance of PI , such as high thermal stability, solvent resistance, wear resistance; and characteristics of microspheres in size and structural. In future, it is used in the catalyst carrier, purification, ion exchange. Currently, polyimide microspheres are mainly the following aspects: entity microspheres of polyimide; composite microspheres of polyimide/inorganic nanoparticle; porous microspheres of polyimide; hollow microspheres of polyimide. The ways of polyimide microspheres prepared are mainly suspension polymerization, dispersion polymerization, re-precipitation method. However, these problems are existed in process of polyimide microspheres prepared, such as complicated process, particles adhesion, particle size difficult to control, using a large number of stabilizing agents.Polymerization of precipitation has these features with the process simple, not adding stabilizing agents. Experiment examines the following aspects:①Preparation of polyamic acid (PAA) microspheres by polymerization;②Polyimide microspheres prepared with imidization of polyamic acid by the process conditions;③The thermal transition behavior of polyimide microspheres. (1) Preparation of polyamic acid (PAA) microspheres by precipitation methodThe polyamic acid (PAA) microspheres were prepared using the precipitation method in solvents such as methanol, ethanol, tetrahydrofuran (THF), Methyl ethyl ketone(MEK) N-metyl-2-pyrrolidone (NMP). Scanning electron microscopy (SEM) photographs show better PAA microsphere morphology while methyl ethyl ketone as solvent, and the average particle size is about 8.8μm. Subsequently, in order to get the larger size microspheres, methyl ethyl ketone (MEK) and N-methyl pyrrolidone (NMP) was used as mixed solvent for the reaction system. When the volume ratio of MEK and NMP was 8:1, the particles have better microspheres morphology, and average particle size is 16.5μm. The particle size increased with increasing the volume ratio of NMP.(2) Polyimide microspheres prepared with imidization of polyamic acid by the process conditionsBased on the front work, selecting the PAA microspheres at the volume ratio of MEK and NMP 8:1, two different forms of heating their sub-amination, such as temperature gradient heating and other time intervals, eventually PI microspheres were obtained. SEM images show microspheres morphology of PI by the temperature gradient heating are better than by the other time intervals; infrared spectroscopy displays the temperature gradient heating better the thermal of PI microspheres performance by temperature gradient heating was better than by the other time intervals .(3) The thermal transition behavior of polyimide microspheresThis article attempts to study the thermal preliminary behavior of polyimide microspheres. Gel permeation chromatography (GPC) analysis three different molecular weight of PI microspheres. The show that glass transition temperature (Tg) of polyimide microspheres increases with the number average molecular weight increasing.