Synthesis And Characterization Of Polysilsesquioxane/Crown Ether-Polyimide Nanocomposite Films

Polyimide(PI) possesses high performances including mechanical properties, thermal stability and chemical resistance. It can be widely used in high-tech fields such as electronic and microelectronic industry. The intrinsic dielectric constant(k) of conventional PIs locates in the range from 3.1 to 3.6, and k lower than 2.5 is usually required for minimizing the power dissipation and delay of signal transmission in interlayer dielectrics for the ultra-large scale integrated circuits. When PI is modified by polysilsesquioxane, amino groups in polysilsesquioxane will react with anhydride and carboxyl groups in PAA. Polysilsesquioxane endows PI with better thermal and mechanical properties, as well as a lower k. When PI is modified by crown ether(CE), molecules of CEs will encircle the macromolecular chains of PI to construct special necklace-like interlocking CEs-PI composites. The structure of inclusion complex endows PI with excellent properties such as high stiffness and toughness, and low k.Octa(aminopropyl) silsesquioxane(OAPrS) is introduced to prepare PI nanocomposite films in the paper. Furthermore, OAPrS is attached to CEs-PAA composites to prepare polysilsesquioxanes/crown ether-polyimide nanocomposite films, which are expected to possess low-k(<2.50), excellent mechanical properties, and thermal property. Thus, OAPrS/PI nanocomposite films and OAPrS/CE-PI nanocomposite films are prepared through in-situ polymerization process.Each of the two kinds of PI nanocomposite films mainly has an amorphous peak in XRD patterns. The dramatical decrease of the crystallization peak proves that there exists the sufficient reaction between PI and polysilsesquioxane, and the introduction of CE can accelerate the formation of amorphous structure in PI. SEM patterns show that there is a homogeneous morphology consisted of the additives and the matrix.From the UV transmittance spectrum, it is shown that the introduction of OAPrS lowers the transmittance of PI films, while the introduction of CE may make up the loss. PI films modified by polysilsesquioxane possess the higher thermal degradation temperature and more carbon residue, while the addition of CE plays a negative effect on the thermal stability of PI. Thus, Tmax(the temperature at which the maximum weight loss rate occurs) of pure PI, OAPrS-7.5/PI, and OAPrS-7.5/CE6-4PI is 598.6 °C, 602.9 °C, and 594.5 °C, respectively. Their carbon residue at 900 °C is 58.1 wt%, 59.9 wt%, and 54.0 wt%, respectively. The glass transition temperature(Tg) and storage modulus(E’) of PI increase by the introduction of polysilsesquioxane, and CE causes E’ to a higher value while Tg to a lower value. Tg of pure PI is 346.6 °C, and Tg of OAPrS-7.5/PI and OAPrS-7.5/CE6-4PI is 360.1 °C and 317.6 °C, respectively. The introduction of polysilsesquioxane is beneficial to the strength and stiffness of PI, while is the unfavorable factor for the toughness of films. Compared to pure PI, Young modulus of OAPrS-7.5/PI increases from 2.81 GPa to 4.40 GPa, tensile strength increases from 119.3 MPa to 132.2 MPa, the elongation at break decreases from 22 % to 6 %, and the energy to tensile fracture decreases from 20.9 MJ/m3 to 5.2 MJ/m3. As CE is added, the strength and stiffness of PI enhance further, and toughness can be compensated at the same time. Young modulus, tensile strength, the elongation at break, and the energy to tensile fracture of OAPrS-7.5/CE6-4PI are 5.78 GPa, 146.6 MPa, 12 % and 17.3 MJ/m3, respectively. k of PI films declines to a desired value by the co-modification of polysilsesquioxane and CE. k of pure PI is 3.59, and it decreases to 2.51 for OAPrS-10/PI, and 2.43 for OAPrS-10/CE6-4PI. OAPrS/CE-PI nanocomposite films with excellent comprehensive properties are prepared to meet the demand of microelectronic circuit.