Synthesis And Characterization Of A New Type Of Soluble Polyimide Containing Perfluorocyclobutane Rings

Aromatic polyimides are known for their exceptional mechanical, thermal, and electrical properties. Because of this unusual combination of properties, they are widely used in high temperature films, adhesives, and molded parts. Since many PIs are insoluble in organic solvents, they are solution processed in the form of their polyacid precursors, and then it was converted in place to the polyimides. Due to their high glass transition temperatures (T_g), thermoplastic PIs must be melt processed at elevated temperatures. It has limited their utility in microelectronic and composite applications. One of the most successful approaches to improving melt processability has involved the use of monomers with fluorine group.The incorporation of fluorine in polymers is important in the development of advanced materials exhibiting high thermal and thermo-oxidative stability, chemical resistance and superior electrical insulating ability. A relatively recent focus has involved the synthesis of partially fluorinated polyimides, where placement of fluorine-containing segments within the repeating unit has been used to enhance properties.Recently, Babb and his coworkers developed a new synthetic route to monomers terminated with trifluorovinyl ether groups. A new type of polymer containing the perfluorocyclobutyl (PFCB) ring was prepared by the free-radical thermal cyclodimerization of aryl trifluorovinyl ether monomers. Because the PFCB- containing polymers have low dielectric constants, good thermal-oxidative stability, excellent processability, and optical transparency, they have received considerable attention. Thus, it was postulated that PFCB-containing polyimides would also display superior properties that would make them especially attractive for microelectronic, optical and composite applications.In this dissertation, a new type of polyimides containing perfluorocyclobutane rings were synthesized from dianhydrides and a new diamine 1,2,3,3,4,4-hexafluoro-1,2-bis(4-aminophenoxy)cyclobutane, which contains a perfluorocyclobutane (PFCB) ring and was synthesized via fluoroalkylation of commercially available 4-acetamidophenol with BrCF2CF2Br followed by Zn-mediated elimination and exothermic cyclodimerization. Three anhydrides including bicyclo[2.2.1]octane-2,3,5,6-tetracarboxylic 2,3,5,6-dianhydride (BHDA), biphenyltetra-carboxylic dianhydride (BPDA) and benzophenone-3,3',4,4'-tetracarboxylic dianhydride (BTDA) were used respectively. The polymers were characterized by means of FT-IR, inherent viscosity, solubility experiment and thermal analysis including differential scanningcalorimetry (DSC) and thermogravimetric analysis (TGA). TGA studies indicate that the polymers were all stable up to 480 °C. DSC results indicate that two of the three polymers have a Tg below 150°C. The polymers were found to be soluble in the main commonly used polar solvents, such as DMF> NNfl\ THF. Thus the polymers containing PFCB rings exhibited excellent solubility and processability.