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An Investigation of Novel Isomeric Polyimide/Sio2 Hybrid Material

K.UMAKANTH ,H.R.SREEPAD

A novel isomeric polyimide/SiO2 hybrid material was successfully prepared through sol–gel technique, and its structure, thermal properties and nanoindenter properties were investigated. The researches on solubility and thermal properties of PEIPTES show that it can be used for modifying nano-SiO2 precursor. Then the PEIPTES solution and the nano-SiO2 precursor were mixed for 6 h to let the PEIPTES molecules react with the nano-SiO2 precursor, and modified nano-SiO2 precursor was obtained. Thermo gravimetric analyzer, dynamic mechanical thermal analyzer and nanoindenter XP was employed to detect the properties of the materials, the results demonstrated that isomeric polyimide/SiO2 hybrid material has much better thermal properties and nanoindenter properties than those of isomeric polyimide. The discussion covers solubility, thermal and dielectric properties, permeability and perm selectivity for gas separation, and rheology of isomeric polyimides. Several useful general rules have been found: i.e. the glass transition temperature of polyimides based on isomeric dianhydrides with a given diamine decreases in the order 3,3′->3,4′->4,4′-dianhydride if the polymers are of comparable molecular weight, whereas the thermal stability and the Tβ/Tg ratio (in absolute temperatures) increase in the order of 3,3′- <3,4′- <4,4′-dianhydride. Polyimides from 3,3′- or 3,4′-dianhydride have higher solubility than those from 4,4′-dianhydride. Polyimides from 3,4′-dianhydrides exhibit much lower melt viscosity than those from the other isomeric anhydrides. The dielectric constants of polyimides derived from m,m′- diamines are lower than those from p,p′-diamines. Polyimides based on 3,3′- or 3,4′-dianhydrides have higher permeability and slightly lower perm selectivity than polyimides based on 4,4′-dianhydrides.