A Rational Bottom-Up Chemical Synthesis Of Graphene

Graphene, a recently discovered novel carbon material possesses many unique chemical and physical properties because of its unusual two-dimensional (2D) hexagonal network structure of sp2-hybridized carbon atoms. Developing novel synthesis methods of graphene has become a very popular research topic in graphene chemistry field. There are numbers of synthesis methods of graphene, including mechanical exfoliation, graphite oxide-reduction, chemical vapour deposition, epitaxial growth, arc discharge, organic synthesis and so on. Among them, organic synthesis of graphene is attracting more and more attention because of its advantage of preparing graphene with few defects in high efficiency.Explorations of pure organic synthesis approaches starting from precursor small molecules towards grapheme have fascinatingly attracted many organic synthetic chemists. In this thesis, we present a chemical synthesis approach towards graphene by flash pyrolysis of poly(2,5-dichlorophenylene-1,4-ethynylene), which can be efficiently synthesized from 2,6-dichloroaniline. The synthetic logic can be divided into two steps:(1) building a graphene one-dimensional skeleton, poly(phenylene vinylene) chain, starting from a single-aromatic-ring small molecule; (2) lengthening the one-dimensional skeleton in parallel and orthogonal directions to construct graphene two-dimensional network by thermal cyclodehydrogenation. This thesis can be divided into two parts:1. The poly(2,5-dichlorophenylene-1,4-ethynylene) was efficiently prepared by four-step syhthesis from 2,6-dichloroaniline, a single-benzene-ring molecule. The fluorescence and electrochemical behaviors of poly(2,5-dichlorophenylene-1,4-ethynylene) were examined by fluorescence spectrum, ultraviolet visible spectrum (UV-vis), cyclic voltammetry (CV), thermogravimetric analysis (TGA). A flash pyrolysis of poly(2,5-dichloro phenylene-1,4-ethynylene) gave FP-1000 product sample which was characterized by Raman spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The analysis results show that FP-1000 has a characteristic foiled layer structure of graphene, majority of these nanoobjects have heights around 0.6-0.7 nm, corresponding to the thickness of a single or double layer graphene. Plenties of internal hollow defects were found in the layers as well.2. A series of side-chain liquid crystalline polymers (LCPs) with polysiloxane backbones have been synthesized by grafting acetylene-terminated or alkene-terminated mesogenic monomers to polymethylhydrosiloxanes (PMHS) via hydrosilylation. Their properties were studied in detail by a combination of 1H-NMR,29Si-NMR, GPC, TGA, DSC, POM and SAXS. The results show that both the glass transition temperatures and the the LC-isotropic transition temperatures of two polysiloxane-based LCPs PVLC1 and PVLC2 prepared by alkene-hydrosilylation are respectively lower than those of their alkenylsilane-analogues PALC1 and PALC2. Compared with PVLC1 and PVLC2, PALC1 and PALC2 become more prone to form smectic phases. This scenario indicates that alkenylsilane linkers, compared with traditional alkylsilane linkers, are much more rigid and markedly influence the mesomorphic properties of LCPs.