Study On Synthesis And Properties Of Novel Soluble Polyimides Containing Irregular Structure In Main Chain

Polyimides, as aromatic polymers, have exhibited a series of outstanding characters, such as excellent thermostability, mechanical and electrical properties, as well as ability of solvent-resistance, so that they are being widely employed in the aerospace, microelectronics, optoelectronics, composites and so on. 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. Based on the viewpoint of molecular design, novel pyridine-containing and unsymmetrical acylamide-containing aromatic diamines were designed and synthesized, which structures were confirmed by elementary analysis, FT-IR, NMR and MS. Their solubility, thermal property, mechanical property, aggregate structures, and dielectric property were investigated and discussed.Two novel pyridine-containing aromatic diamine monomers, i.e.4-phenyl-2,6-bis[3-(4-aminophenoxy)-phenyl]-pyridine(m-PAPP),and 4-phenyl-2,6-bis[3-(4'-ami no-2'-trifluoromethyl-phenoxy) phenyl] pyridine (m-PAFP), were successfully designed and synthesized as a potentially convenient condensation monomer to form pyridine-containing polyimides. Meanwhile, series of pyridine-containing polyimides were synthesized from the resulting diamine monomer with several aromatic dianhydrides by a two-step procedure, and the polyimides obtained were characterized detailedly. Most of the resulted polyimides were soluble in common organic solvents. The resulting strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 403℃and the glass transition temperature in the range of 180-264℃, as well as outstanding mechanical properties with the tensile strengths of 90.1-114.1 MPa, tensile modulus of 1.16-1.89 GPa and elongations at breakage of 8.9-15.7%. The dielectric constants of FPIs at 1 MHz and 10 MHz were in the range of 2.84-2.98 and 2.64-2.74 respectively.The two unsymmetrial aromatic diamine monomers,3,4'-Diamino ben-zophenone (3,4'-DABP) and 4"-diaminophenyl-3',4-diacylamidebenzophenone (DAAP), were successfully synthesized using 4-nitrobenzoic acid as starting material and employed in the preparation of novel polyimides by polycondensation with several aromatic dianhydrides via the two-step method. The resulting polyimides poly(amide-imide)s hold inherent viscosity values of 0.37-0.98 dL/g and were easily dissolved in highly dipolar solvents. The polyimides and poly(amide-imide)s show good thermal and thermo-oxidative stabilities with the glass transition temperatures (Tg) of 156-242℃, the temperature at 5% weight loss of 495-593℃in air and residual weight retentions at 800℃in air of 55-71%, meanwhile, they exhibit outstanding mechanical properties with the tensile strengths of 78.7-108.3 MPa, elongations at breakage of 11.1-15.7% and tensile modulus of 1.28-2.06GPa.