Thermal and Mechanical Properties of Phenylethynyl-Containing Imide Oligomers Based on Isomeric Biphenyltetracarboxylic Dianhydrides

In order to further improve both processability of imide oligomers containing pendent or/and terminal phenylethynyl groups and their cured T-g values without sacrificing mechanical properties, isomeric dianhydrides, 2,2',3,3'-biphenyltetracarboxylic dianhydride (3,3'-BPDA) or 2,3',3,4'-biphenyl tetracarboxylic dianhydride (3,4'-BPDA), were introduced into main chain. The rigid and bent structure of the isomeric BPDAs can provide a good combination of melt flow while maintaining a high T-g. Phenylethynyl containing oligoimides were prepared from the reaction of isomeric dianhydrides (3,3'-BPDA, 3,4'-BPDA and 4,4'-BPDA), 4,4'-oxydianiline (4,4'-ODA), 3,5-diamino-4'-phenylethynyl benzophenone (DPEB) and 4-phenylethynylphthalic anhydride (4-PEPA) or phthalic anhydride (PA) at an approximate number average molecular weight of 2500 and 5000 g mol(-1). The imide oligomers from 3,3'-BPDA and 3,4'-BPDA exhibited good processability. The 3,3'-BPDA-based imide oligomers exhibited slightly lower melt viscosity and the cured resins exhibited similar T-g values compared with those from 3,4'-BPDA. OI-7 and OI-8 each with a molecular weight of 2500 g mol(-1) had lower melt viscosities of 25 Pa s (342 degrees C) and 178 Pa s (344 degrees C) and higher cured T-g at 367 degrees C and 365 degrees C. The cured films from OI-7, OI-8 showed good tensile properties and the elongations at break were around 10%. The neat resins from OI-7 and OI-8 had higher compressive strengths of 200 and 190 MPa. G827/OI-7 and G827/OI-8 exhibited comparable mechanical properities: flexural strengths of 1714 and 1826 MPa, flexural modulus of 130 and 124 GPa, and interlayer shear strengths of 95 and 101 MPa, respectively.