Abstract
A novel PMR-type polyimide based on 3,3′4,4′-oxydiphthalic dianhydride (ODPA), 4,4′-methylenedianiline (MDA) with nadic ester (NE) endcaps was studied. Its random copolymers, which incorporated pyromellitic dianhydride (PMDA) and p-phenylenediamine (PPD) into the backbone, were synthesised. They are characterised in abbreviation as OPM (ODPA/PMDA-MDA) and OMP (ODPA-MDA/PPD) respectively. Oligomers with various molecular weights and components were synthesised, in order to compare the influence of the chemical structure and the crosslink density of polyimides on the final properties. MOPM, which contained an identical backbone to OPM but was terminated with a mono-nadic endcap, was also synthesised to see whether the different endcaps of oligomers could impact enhanced thermal properties. The thermo-oxidative stability, processing and mechanical properties of these polyimides were tested. The results showed that incorporation of PMDA or PPD into the ODPA-MDA homopolyimide (abbreviated as OM) could greatly enhance the Tg, while retaining comparable thermo-oxidative stability and reasonable processing properties.