Zhewen Han

Synthesis of acid-soluble graphene and its use in producing a reduced graphene oxide–poly(benzobisoxazole) composite

A new chemically modified graphene was prepared using carboxylated graphene oxide (GO) and fluorinated poly(hydroxyamide) (6FPHA), the latter is the precursor of fluorinated poly(benzobisoxazole) (6FPBO). The results showed that, unlike common GO, which can only be dispersed in water under neutral or basic conditions, the RGO–6FPBO (reduced graphene oxide–6FPBO) could be stably dispersed in Lewis acids. The RGO–6FPBO–poly(benzobisoxazole) (PBO) composite was achieved by simple solution blending of RGO–6FPBO and PBO in methanesulfonic acid. The obtained RGO–6FPBO–PBO composite films exhibited a dramatic increase in electrical conductivity, by 8 orders of magnitude at the RGO–6FPBO content of 4 wt%, without significantly sacrificing optical transparency. When the content of RGO–6FPBO was higher than 4 wt%, the dielectric constant of the composite film also increased remarkably. The mechanical properties and thermal stability of the composite were also improved by the incorporation of RGO–6FPBO.

Synthesis and photoluminescence properties of polybenzoxazoles containing perylenebisimide functionalized graphene nanosheets via stacking interactions

The stable acidic dispersion of reduced graphene oxide (RGO) is prepared by a non-covalent functionalization method using perylenebisimide-modified fluorinated poly(hydroxyamide) (PTCDA-6FPHA). Then a series of RGO–polybenzoxazole (PBO) composites were prepared by a solution blending method in MSA. The change of perylenebisimide absorption peaks in the UV-Vis absorption spectra indicates that π–π stacking indeed occurs between graphene and perylene rings. The conjugation between functionalized RGO and PBO molecular chains increases the conjugation degree of the composite, since the PTCDA-6FPHA-containing perylene rings have a high π-electron delocalization degree. The energy gap of RGO–PBO composite is 2.72 eV with the absorption edge at 456 nm. The corresponding data of pure PBO film are 2.78 eV and 446 nm, respectively. Moreover, the intensity of the two emission peaks at 442 and 467 nm in the PL emission spectra of RGO–PBO decreases rapidly along with the increase of RGO–PBO ratio. The intensity of the weak emission peak at 622 nm increases with the increase of the RGO–PBO ratio. This behavior can be attributed to the energy transfer between benzoxazole chromophore units and functionalized RGO. Meanwhile, the RGO–PBO composite has outstanding thermal stability.

Protonation Effect of Polybenzoxazole: Experimental Evidence

In order to investigate the protonation effect of polybenzoxazole, a type of soluble thiophene-based polybenzoxazole (PBOP-Th) is synthesized and characterized by the FTIR, 1H-NMR, elemental analysis, thermogravimetric analysis (TGA), UV-Vis and photoluminescence (PL) spectra. Another polymer aminophenols-based polybenzoxazole (PBOP-Ph) was also synthesized as reference polymer. Unlike usual polybenzoxazoles such as poly(p-phenylenebenzobisoxazole) (PBO) and poly(2,5-thienylbenzobisoxazole) (PBOT), PBOP-Th and PBO-Ph have greatly enhanced solubility due to the introduction of isopropylidene and/or thiophene cycle. The effect of protonation on photophysical properties of polybenzoxazoles is studied by an experimental method for the first time. The 30 nm red shift on the UV-Vis and PL spectra of polymer is observed in methanesulfonic acid (MSA) solution compared with that of polymer in neutral N,N-dimethyl fomamide (DMF) solution, which is believed to be due to the protonation effect.