Low dielectric polyimide/poly(silsesquioxane)-like nanocomposite material

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 (PTS) 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 Tg 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 Tg 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 Tg 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–y-PTS films decrease with the PTS content because of the higher free volume and hydrophobicity.