A new type of low dielectric polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid nanocomposite material is successfully prepared from the polyimide (ODA-ODPA) precursor containing phenyltrialkoxysilane IPTS) at two chain ends and monoaryltrialkoxysilane with a self-catalyzed sol-gel process. We employ p-aminophenyltrimethoxysilane (APTS) to provide bonding between the PTS and ODPA-ODA phase, It is shown by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) that the PSSQ-like domain sizes with uniform size are fairly well separated in the hybrid films. The silica domain sizes of 5000-PIS and 5000-PIS-50-PTS films are in the range of 30-100 nm, of 5000-PIS-100-PTS and 10000-PIS-100-PTS in the range of 80-200 and 300-600 nm, respectively. The dielectric constant can be 2.79 for 5000-PIS-140-PTS with fairly good mechanical properties. The PI/PSSQ-like hybrid films have higher onset decomposition temperature and char yield in thermogravimetric analysis (TGA) and higher T-g in differential scanning calorimetry (DSC) than the pure PI. Moreover, the PI/PSSQ-like hybrid films have excellent transparency even under high PTS content. In the series of X-PIS hybrid films, the coefficient of thermal expansion (CTE) below T-g increases with the PI block chain length, but in the series of X-PIS-y-PTS films, it slightly increases with the PTS content. However, above T-g the CTE of X-PIS and X-PIS-24-PTS is much lower than that of the pure PI. The dielectric constant and water absorption of X-PIS-V-PTS films decrease with the PTS content because of the higher free volume and hydrophobicity. (C) 2001 Elsevier Science Ltd. All rights reserved.