Poly(phthalazinone ether sulfone ketone)(PPESK) hollow fiber membrane for gas separation was prepared by dry/wet phase inversion technique in water.The cloud point titration method and the calculation based on linearized cloud point (LCP) curve correlation were employed in the research of the phase separation of PPESK ternary spinning solution.In the PPESK/N

N-dimethylacetamide (DMAc)/gamma-butyrolactone (GBL) and PPESK/DMAc/propionic acid (PA) systems

the theta composition of nonsolvent additive (NSA)/DMAc solvent mixture was determined according to Elias's method.The results showed that the experimental cloud points and the calculated binodal lines based on LCP had a good agreement in the systems of PPESK/DMAc/PA and PPESK/DMAc/water.From the thermodynamics stability of spinning solution and the final performance of hollow fiber membrane

conclusion could be drawn that higher the thermodynamics stability of spinning solution was

higher the gas selectivity of ultimate membrane was.The theta composition of NSA/DMAc solvent mixture played a very important role in the membrane forming.When the NSA content of spinning solution was lower than its content at theta composition

the performance of membrane was excellent

but when the NSA content was higher than the theta composition

the performance of membrane droped sharply.The PPESK hollow fiber membranes had fine mechanical properties.