Polyarylenes: Synthesis and Characterization Towards Advanced Applications

A series of semi-fluorinated and non-fluorinated Diels−Alder step-growth polyarylene polymers and co-polymers were synthesized via typical oil bath heating (days/weeks) and more rapid microwave-assisted polymerization (hours). The polymers were characterized by multi-nuclear (1H, 13C, and 19F) NMR and ATR−FTIR spectroscopy, thermal analysis (TGA, DSC, and DMA), GPC, XRD, water contact analysis (WCA), and refractive index (RI) measurements. The NMR spectra indicated a mixture of para and meta conformations through the polymer backbone increasing to more para with greater fluorine content. Thermal gravimetric analysis revealed the fluorine-containing polyarylenes possessed the highest char yields at almost 80% at 1000 oC under nitrogen, and all the polyarylenes possessed onset of degradation temperatures above 550 oC under nitrogen and air atmospheres. XRD analysis showed more ordering for the fluorine-containing polyarylenes which afforded the high char yields. DMA gave storage moduli values in the range of 1-10 GPa for the polyarylenes. GPC results indicated molecular weights for all samples were above 100 kg/mol. Water contact angles did not change with fluorine content due to the shielding effect of the pendant phenyl groups. However, the refractive index decreased to 1.6497 at 632.8 nm for the polyarylene with the highest fluorine content. A series of six new polyarylene polyimides (PAPI) were prepared from a new diamino-phenylated-phenylene synthesized via a Diels−Alder reaction, followed by a one-step microwave-assisted step-growth polycondensation reaction with a variety of dianhydrides. The polymerizations were optimized from 10 to 30 minutes in reaction time with isoquinoline as catalyst. Yields as high as 99% were achieved using nitrobenzene as the solvent. Semi-fluorinated dianhydrides were included to compare polyimide properties to the non-fluorinated materials. Full characterization was carried out via 1H and 19F nuclear magnetic resonance and attenuated total reflectance Fourier transform infrared spectroscopy. Thermal properties were characterized via thermal gravimetric analysis and differential scanning calorimetry. The onset of thermal degradation was approximately 550 oC in nitrogen and air atmospheres while the char yield at 1000 oC in nitrogen was almost 70%. The semi-fluorinated polyarylene polyimide exhibited the highest char yield. The glass transition temperatures were in the range of 355 to 387 oC, with the semi-fluorinated material possessed the highest Tg. The optical transparency was good in all the materials, with the semi-fluorinated material having the largest optical window in the UV-Vis region. The polymers were colorless or pale-yellow solids. Solubility was excellent in chloroform, tetrahydrofuran, toluene, and cyclohexanone