Synthesis And Characterization Of Fluorinated Polyamides And Polyimides Containing2,6-Diphenylpyridine Groups

In this dissertation, the recent progress on the research of2,6-diphenylpyridine-based polyamides and polyimides was investigated. The main works include thefollowing four parts:1. The pyridine-based dinitro compound,4-(4-trifluoromethylphenyl)-2,6-bis(4-nitrophenyl)pyridine (BNTP), was successfully prepared from a modifiedChichibabin reaction of4-nitroacetophenone and4-trifluoromethyl benzaldehyde. Thepyridine-based diamine monomer,4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine (BATP), was then obtained from a reduction of the resulting dinitrocompound. Homoplastically, the other diamine monomer,1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (BATB), was synthesized by a nitro reduction of1,4-bis(4-nitro-2-trifluoromethylphenoxy), which was acquired by reacting hydroquinone with2-chloro-5-nitrobenzotrifluoride. A series of aromatic co-polyamides (co-PAs)containing2,6-diphenylpyridine units were then achieved by a conventional solutionpolycondensation of different ratio of BATP/BATB and paraphthaloyl chloride. Theinherent viscosities of the obtained co-PAs ranged from0.58to1.10dL/g. The glasstransition temperatures of these co-PAs ranged from266to358°C and thedecomposition temperature at5%weight ranged from428to473°C in nitrogen.Meanwhile, all the co-PAs left around53%residual even at750°C in nitrogen. Theco-PAs were soluble in dipolar aprotic solvents such as NMP, DMAc and DMSO, andalso in a less efficient solvent such as THF and pyridine. Furthermore, co-PAsexhibited outstanding mechanical properties with tensile strengths of49.6–70.1MPa,modulus of elasticity of0.84–1.01GPa and elongations at break of58.6–110.2%. Inaddition, the aromatic co-polyamides films exhibited good optical transparency andlow moisture uptakes of0.98–1.21%.2. The synthesis of2,6-diphenylpyridine-based polyimides (PI) involved reactingthe diamine (BATP) and various dianhydrides at ambient conditions in a dipolaraprotic solvent (DMAc) to yield intermediary poly(amic acid)s which were thencyclized into the final polyimides. The poly(amic acid)s obtained displayed inherentviscosities ranging from0.49to0.94dL/g. The polyimides based on BPDA、HQDPA、ODPA and TDPA were partially soluble in common polar aprotic solventsonly on heating. While the polyimide based on6FDA showed excellent solubilitybeing attributed to the low cohesion energy provided by fluorinated groups. It wassoluble in dipolar aprotic solvents such as NMP, DMAc and DMSO and also in a lessefficient solvent such as THF and pyridine. The glass transition temperatures of thesePIs ranged from324to416°C and the decomposition temperature at5%weightranged from538to581°C in nitrogen. Meanwhile, all the PIs left above58% residual even at750°C in nitrogen. The results showed that the wholly aromaticpolyimides maintained desirable high temperature characteristics. Furthermore, the2,6-diphenylpyridine-based PI films exhibited desirable mechanical properties withtensile strengths of68.03–131.65MPa, modulus of elasticity of1.1–1.99GPa andelongations at break of7.03–27.15%. In addition, the aromatic polyimide filmsexhibited good optical transparency, low moisture uptakes of0.56–1.27%andrelatively low dielectric constants of3.49–4.0.3. A series of poly(amic acid)s were achieved by a solution polycondensation ofdifferent ratio of BATP/BATB with3,3’,4,4’-biphenyl tertracarboxylic dianhydride.And the intermediate poly(amic acid)s was then converted to the final polyimides by athermal imidization route. The poly(amic acid)s obtained displayed high inherentviscosities ranging from0.89to1.77dL/g. The wholly aromatic polyimides werepartially soluble in common polar aprotic solvents only on heating. While the whollypolyimides maintained desirable temperature characteristics. The glass transitiontemperatures of these PIs ranged from282to347°C and the decompositiontemperature at5%weight ranged from567to581°C in nitrogen. Meanwhile, all thePIs left above57%residual even at750°C in nitrogen. Furthermore, the PI filmsexhibited outstanding mechanical properties with tensile strengths of109–120MPa,modulus of elasticity of1.34–1.52GPa and elongations at break of27.8–48.7%. Inaddition, the PI films exhibited good optical transparency, relatively low moistureuptakes of1.13–1.61%and low dielectric constants of3.59–4.01.4. A series of poly(amic acid)s were achieved by a conventional solutionpolycondensation of different ratio of BATP/BATB with4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). And the intermediate poly(amic acid)s wasthen converted to the final polyimides containing2,6-diphenylpyridine groups by athermal imidization route. The polyimids obtained displayed inherent viscositiesranging from0.58to0.89dL/g. The wholly aromatic polyimides were soluble indipolar aprotic solvents such as NMP, DMSO and DMAc, and also in a less efficientsolvent such as THF and pyridine. The glass transition temperatures of these PIsranged from272to338°C and the decomposition temperature at5%weight rangedfrom522to531°C in nitrogen. The results showed that the2,6-diphenylpyridine-based polyimides maintained desirable temperaturecharacteristics. Furthermore, the PI films exhibited outstanding mechanical propertieswith tensile strengths of107.2–153.2MPa, modulus of elasticity of1.35–1.8GPa andelongations at break of13.2–19.6%. In addition, the PI films exhibited excellentoptical transparency above79.5%at500nm, very low moisture uptakes of0.57–0.73%and relatively low dielectric constants of3.17–3.43.