A series of novel-poly(amide-imide)s (PAIs) containing sulfur elements were synthesized and characterized.The flexible sulfur-containing groups

either the linear thioether linkage or cyclic thianthrene group were introduced into the PAIs in order to increase the refractive indices and decrease birefringences of the polymers.Thus

an aromatic diacid compound 1

4-bis(4-trimellit-imidophenylenesulfanyl) benzene (BTPB) was first synthesized from a sulfurcontaining diamine 1

4-bis(4-aminophenylenesulfanyl) benzene (2SPDA) and trimellitic anhydride （TMA）.Then

BTPB was polymerized with two aromatic diamines with high sulfur contents

4

4′-thiobis［(p-phenylenesulfanyl) aniline］ (3SDA) and 2

7-bis(4-aminophenylenesulfanyl)-thianthrene (APTT)

respectively to afford two PAIs.The obtained high-molecular-weight PAIs with the inherent viscosities of 1.06～1.17 dL/g are soluble in N-methyl2-pyrrolidinone (NMP) at room temperature.The PAI films exhibit good thermal stability up to 440℃ and glass transition temperatures higher than 190℃.In addition

the PAI films show good optical transparency in the visible light region with the cutoff wavelengths around 400 nm and optical transmittances higher than 90% at 500 nm.The high sulfur contents and the flexible thioether linkages endow the PAI films with refractive indices higher than 1.73 and birefringences lower than 0.04 at 632.8 nm.