Study On Preparation Of New Asymmetrical Aromatic Diamines And Related Polyimides

Aromatic polyimides possess excellent thermal and mechanical, electrical, and chemical properties. Therefore, they are being used in many high-technology applications such as microelectrics and aeronautics. However, the commercial use of these materials is often limited because of their poor solubility, and high softening or melting temperatures. To overcome these problems, more and more attempts have been focused on the preparation of novel polyimides with improved properties.This paper summarizes the structural characteristics of polyimides with excellent properties, and analyzed the contributions of several structural modification methods to each aspect of polyimide properties. Three novel aromatic diamines were designed and prepared based on the viewpoint of molecular design, which structures were confirmed by elementary analysis, FT-IR, NMR and MS. Derived from the resulted diamines and dianhydrides, four series of novel polyimides were successfully synthesized. The polymer constructions were confirmed by elementary analysis, FT-IR and1H-NMR. Their solubility, thermal property,, aggregate structures, and dielectric property were investigated and discussed.A series of new polyimides were synthesized from an unsymmetrical aromatic diamine,3,4’-bis(4-aminophenoxy)-benzophenone (BABP) with various commercially available aromatic dianhydrides. The resulting polyimides exhibits excellent film-forming capability and high thermal resistance and exhibited excellent solubility in polar solvents, such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidinone.A novel method for the preparation of an asymmetric fluorinated aromatic diamine,3,4’-bis(4-arnino-2-trifluoromethyl-phenoxy)-benzophenone was investigated. This new diamine containing trifluoromethyl side group was synthesized from the nucleophilic substitution reaction of2-chloro-5-nitrobenzotrifluoride and3,4’-dihydroxybenzo phenone in the presence of potassium carbonate, followed by catalytic reduction with SnCl2·6H2O and concentrated hydrochloric acid. This novel diamine was used to react with different commercially available aromatic tetracarboxylic dianhydrides to prepare polyimides via thermal or chemical imidization. The polyimide properties such as inherent viscosity, solubility, thermal and surface properties were investigated to illustrate the contribution of the trifluoromethyl group and the asymmetry structure of the polyimide. The polyimides obtained had good thermal stability and the glass-transition temperature values ranged from225to267℃. All of these novel polyimides held10%weight loss at the temperature above543℃in air and left more than47%residue even at800℃in nitrogen. The inherent viscosities of the obtained polyimides were above0.73dL/g and were easily dissolved in both polar, aprotic solvents and some low-boiling-point solvents. Moreover, these PI films had dielectric constants of2.94-3.53(1KHz), with moisture absorption in the range of0.07-0.34wt%. In comparison with the analogous symmetric PIs6series based on4,4’-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone, the PIs5series revealed better solubility, low dielectric constant and moisture absorption.A new kind of aromatic unsymmetrical diamine monomer,2’-(4-amino phenoxy)-7’-(2-trifluoromethyl-4-aminophenoxy)-spiro(fluorene-9,9’-xanthene), was successfully synthesized using9-fluorenone as starting material. A series of new polyimides were synthesized from the diamine with various commercially available aromatic tetracarboxylic dianhydrides via a conventional two-stage process with the thermal or chemical imidization of the poly(amic acid) precursors. The results polyimides had inherent viscosities of0.56-1.23dL/g and were easily dissolved in both polar, aprotic solvents and some low-boiling-point solvents. The strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at5%weight loss) above477℃and glass-transition temperatures in the range of222-278℃, These films also held dielectric constants of2.83-3.02(1KHz). Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.