Thermosetting phenylethynyl terminated polyimides are well known for their super thermo-oxidative stability and excellent toughness

and have been widely used in aerospace area.PETI-5 (PhenylEthynyl Terminated Imide-5) developed by NASA is the-state-of-art of this type polyimides

while it is a semi-crystalline polyimide with melting temperature of 353℃ near the crosslinking temperature of phenylethynyl groups

which made it difficult for PETI-5 to fabricate complex shape parts.In the pursuit of novel phenylethynyl terminated polyimides with high melt processability

researchers have developed several polyimides by introduction of fluorine groups and twisty structures.In this paper

a series of oligoimides (PIO) with calculated molecular weight of 5000 were prepared using flexible dianhydride of 4

4′-oxydiphthalic anhydride (ODPA)

and mixtures of two diamines of 1

3-bis(4-aminophenoxy)benzene (1

3

4-APB) and 3

4′-oxydianiline (3

4′-ODA) in the presence of 4-phenylethynylphthalic anhydride (4-PEPA) as endcapping agent in order to enhance the processability.In addition

oligoimides (PIB) using 3

3′

4

4′-biphenyltetracarboxylic-dianhydride (s-BPDA) were also prepared for comparison.Effects of the kind of dianhydride and diamine on their properties and melt processabilities were systematically investigated.Experimental results indicated that PIO was amorphous in nature

and exhibited low melt viscosity and high melt viscosity stability at elevated temperatures

and with the increase of the content of 1

3

4-APB the melt viscosity decreased correspondingly.The PIB is semi-crystalline in nature and exhibited high melt viscosity at elevated temperatures

meanwhile

the melt temperature of PI-B was close to the cure temperature of phenylethynyl groups

which reduced the processability.The molecular weight-controlled oligoimides could be thermally cured at 371℃ to yield thermosetting polyimides by polymer chain extension and crosslinking of phenylethynyl groups.All cured resins showed good thermal stability with 5% weight loss temperature of500℃

and high glass transition temperatures of243℃.In addition

with the increase of the content of 1

3

4-APB

the glass transition temperatures of PIO cured resin decreased from 281 to 243℃.PIO-2 cured resin also exhibited good mechanical properties with tensile strength of 102 MPa

tensile modulus of 1.8 GPa

high break elongation of 10%

flexural strength of 142 MPa and flexural modulus of 3.1 GPa.