Preparation of polyimide particles by precipitation polymerization

Polyimide particles were prepared from 3,3', 4,4'-benzophenon tetracarboxylic dianhydride (BTDA) and various aromatic diamines in polar amide-type solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), and N, N-dimethylformamide (DMF) by precipitation polymerization. SEM demonstrated that the shape of these particles was a sphere, a formlessness or a form like a pie. The shapes and the diameters were varied by both the affinity of polyimides for reaction solvents (the difference of solubility parameter values between polyimide and solvent) and the average molecular weight of polyimides (the intrinsic viscosity of polyimides). Spherical particle sizes were in the range from 2.5 to 5.6 mu m. On the other hand, the sizes of polymeric aggregates in a formless fashion were in the range from 20 to 60 mu m. Thermogravimetric analyses indicated that these polyimides were fairly stable up to 500 degrees C, and the 10% weight loss temperatures in nitrogen and in air were observed in the range of 548 similar to 573 degrees C and 513 similar to 544 degrees C, respectively. These polyimides had melting points in the range of 408 similar to 480 degrees C, and glass transition temperatures were recorded in the range of 273 similar to 378 degrees C (DSC).