A new copoly(ether imide) 1a was synthesized from 4,4'-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA) and 4,4'- bis [3'-trifluoromethyl-p-aminobiphenyl ether)biphenyl (TFBB) with 20 wt% loading of 3,5-diaminobenzoate terminated polydimethylsiloxane (DBPDMS) by solution imidization technique. The copoly(ether imide) showed a glass transition temperature of 272 degrees C by differential scanning calorimetry and of 300 degrees C by dynamic mechanical analysis, respectively. The polymer showed thermal stability up to 371 degrees C for 5% wt loss in synthetic air. Dynamic mechanical analysis showed storage modulus as high as 1.62 GPa at 40 degrees C. In the DMA plot a distinct sub Tg relaxation was observed at 130 degrees C. The copolyimide formed tough transparent film, with tensile strength up to 47 MPa, a modulus of elasticity up to 1.83 GPa and elongation at break up to 65%. Thermal, mechanical and surface properties of the copoly(ether imide) have been evaluated and compared with the already reported analogous random copoly(ether imide) containing siloxane unit in the main chain and with the homopolyimide without siloxane unit.