A series of molecular-weight-controlled imide resins end-capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4-bis(4amino-2-trifluoromethylphenoxy)benzene and 1,3-bis(4-aminophenoxy)benzene with 4,4'-oxydiphthalic anhydride in the presence of 4-phenylethynylphthalic anhydride as an end-capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular-weight-controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280 degrees C. The molecular-weight-controlled imide resins could be thermally cured at 371 degrees C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500 degrees C and high glass-transition temperatures greater than 290 degrees C, and good mechanical properties, with flexural strengths in the range of 140.1-163.6 MPa, flexural moduli of 3.0-3.6 GPa, tensile strengths of 60.7-93.8 MPa, and elongations at break as high as 14.7%. (C) 2007 Wiley Periodicals, Inc.