Preparation of semi-interpenetrating networks of phthalonitrile and polyetherimide resin: study of their curing characteristics and thermal properties

Present embodiment is an account of work done on impregnation of thermoplastic polyether imide (PEI) [ULTEM 1000] into high-temperature biphenyl-based phthalonitrile (PN) thermosetting resin to form a semi-interpenetrating network (s-IPN) in order to find an optimum composition with little compromise on glass transition temperature (Tg) and thermal stability of base resin system. The PEI has been cured with PN resin in varied ratios of 5-30 mass% in arithmetic progression to study its effect on thermal and physical properties. Fourier transform infrared spectroscopy, differential scanning calorimetry and thermos-gravimetric (TG) measurements of the s-IPN compositions were carried out to assess the extent of curing, curing enthalpy, glass transition (T-g), thermal stability and char yield, respectively. The dynamic mechanical analysis (DMA), measurements were done to ascertain the effect of PEI component in PN system on its storage modulus, T-g under dynamic load with respect to temperature. PN95 composition having PN/PEI ratio in 95:05 stoichiometry has demonstrated the best desirable properties with respect to PEI content with least compromise in Tg temperature. More than 5 mass% PEI has resulted in drastic change in T-g of s-IPN from > 673 K to 525 K in case of 10 mass% PEI as evaluated by DMA. The morphological analysis of 30% PEI-containing s-IPN showed interesting cross-linked patterns probably formed by the fibrillar orientation of the thermoplastic resin in the PN matrix.