A Study on Preparation and Characteristics of Polyimide /Poly (silsesquioxane)-like Nanocomposite Material

• Main Authors: Mei-Hui Tsai, 蔡美慧
• Other Authors: Wha-Tzong Whang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/07835385883202358885

博士 === 國立交通大學 === 材料科學與工程系 === 89 === Synthesis of low dielectric polyimide/poly(silsesquioxane)-like (PI/PSSQ-like) hybrid nanocomposite material and their dynamic mechanical properties and high temperature lifetime were described in this thesis. The APTS-PAA oligomers were prepared by the reaction of 4,4′-Diaminodiphenyl ether (ODA) and the 3,3′-Oxydiphthalic anhydride (ODPA) in the presence of p-Aminophenyltrimethoxysilane (APTS). APTS controls the polyimide block chain length (X) ranging from 3000 to 20000 g mole-1 and end-group functionality. The PAA-PTS oligomers were prepared by phenyltrialkoxysilane (PTS) and APTS-PAA. The X-PIS and X-PIS-y-PTS (PI/PSSQ-like) hybrid films were obtained by self-catalyzed hydrosis/condensation the APTS-PAA and PAA-PTS, which are designed to form three-dimensional structure with linear polyimide block and crosslinked PSSQ-like structure. In this article, we intend to correlate the properties with the silica component, the PSSQ-like content, the polyimide block chain length and the crosslinking density. The influence of composition of the PI/PSSQ-like on their morphology, thermal stability, phase transitions, dielectric constants, thermal expansion coefficient, moisture absorption, optical transparency in visible, dynamic mechanical properties and high temperature lifetime. In the first part of this thesis, the PSSQ-like nanocomposite domain sizes with uniform size are fairly well separated in the hybrid films by transmission electron microscope (TEM) and scanning electron microscope (SEM). Moreover, the PI/PSSQ-like hybrid films have excellent transparency even under high PTS content. The lowest dielectric constants of the nanocomposite in the series of 5000-PIS-140-PTS and 10000-PIS-100-PTS are 2.79 and 2.85 respectively. The PI/PSSQ-like hybrid films have higher onset decomposition temperature and char yield in thermogravimetric analysis (TGA) and higher Tg in differential scanning calorimeter (DSC) than the pure PI. In the series of X-PIS hybrid films, the coefficient of thermal expansion below Tg decreases with the APTS content, and in the series of X-PIS-y-PTS films, it slightly increases with the PTS content. However, above Tg the coefficient of thermal expansion of X-PIS and X-PIS-24-PTS is much lower than that of the pure PI. The dielectric constant, density and water absorption of X-PIS-y-PTS films decrease with the PTS content because of the higher free volume and hydrophobicity. The second part of this thesis describes dynamic mechanical properties of PI/PSSQ-like hybrid films. In the series of X-PIS hybrid films, decreasing the PI block chain length enhances the storage modulus, tensile modulus and Tg, but reduces the α-relaxation damping peak intensity and elongation. The activation energy of the α-transition depends on the chain length of the PI block. A maximum value is shown at the chain length of 10000 g/mole. In the series of X-PIS-y-PTS films with a constant PI block length, the storage modulus, tensile modulus, Tg, α-relaxation damping peak intensity and activation energy decreases with the PTS content. The third parts of this thesis focus on high temperature lifetime of PI/PSSQ-like hybrid films. Decomposition kinetics in thermogravimetric analysis (TGA) and dynamic mechanical relaxation in dynamic mechanical analysis (DMA) reveal that the PI/PSSQ-like hybrid films have longer lifetime (more reliable) in the thermal and mechanical characteristics than the pure PI. Even just 2 wt % of APTS in the PI/PSSQ-like hybrid film can significantly promote the service lifetime as much as at least four times in TGA decomposition kinetic study. The dynamical relaxation data are well fitted to the calculated WLF (Williams-Landel-Ferry) master curves. In the series of X-PIS hybrid films, decreasing the PI block chain length increases the decomposition activation energy, service lifetime (in both TGA and DMA), and relaxation modulus. In the series of X-PIS-y-PTS hybrid films, the decomposition activation energy and lifetime (in TGA) increase with the PTS content. Interestingly, the dynamic mechanical relaxation modulus of 10000-PIS-100-PTS film is lower than that of the corresponding 10000-PIS film at frequency > 102 rad/sec, but higher at frequency < 102 rad/sec. The former has a lower relaxation time than the latter at the modulus 5 ×108 Pa, but the relaxation time of the former becomes higher at 5 ×107 Pa.