A novel unsymmetrical dianhydride containing 4-(4-hydroxylphenyl)-2

3-phthalazin-1-one was svnthesized in order to improve the solubility of aromatic polyimides according to the principle of designing new monomers．This article reported a series of polyimide random copolymers derived from 4

4’-diamino diphenyl sulfone(DAPS)

4

4'-oxyl dianiline(ODA)and the new dianhydride-2-(3

4-dicarboxyl-phenyl)-4-(3’

4’-dicarboxyl．phenyl-oxyl)．phenyl-2

3-phthalazine-1-one dianhydride (DAH4) by“one-step”solution DolyoDndenSation in m-cresol with catalystic amount of isoquinoline at 200℃．Some properties of the copolymerS were investigated by DSC

TG and mechanical analysis．The result shows that the ηinh of copolymers is between 0.64 to 0.71 dL／g in m-cresol at 25℃

and the Tg of the copolylTters are higher than that of Durt poliymides containing 4

4'-oxyl dianiline(polymer 5)．The relationship between Tg and mole percent of DAPS is not obvious．Degradation temperature for 5% weight loss (Td5)of the copolymers occurs all above 470℃ in air．The mechanical properties of the copolymers age lower owing to introducing suIfone groups into polymer’s backbone．In sharp contrast

the copolymers have good solubility and can he easiIv soluble in 1

1

2

2．tetrachloroethane (TCE)

N

N-dimethylacetamide(DMAc)

N- methyl-2-pyrr01idinone (NMP)

m-cresol and pyridine．Furthermore

the copolymers have better solubility in dimethyl sulfoxide (DMSO) and chloroform than the polyimide derived from DAH4 and ODA．