Synthesis And Characterization Of Polysilanes With Functional Groups

In recent years, polysilanes have been attracted tremendous interests due to their unusual electrical and optical properties, which are widely useful functional materials as semiconductors, photoconductors, nonlinear optical materials, and so on. The unique electrical and optical properties of polysilanes do not only derive from the extensive delocalizaion of σ-electron along the Si-Si backbone, but also extremely influenced by the substituent groups. However, the introduction of reactive organic side groups into polysilanes through direct polymerization of functionalized monomers is limited to the species of silane and the harsh reaction conditions. Hence, the modification of polysilanes could be an alternative method to resolve the above problem, which can effectively introduce reactive side groups to the backbone of polysilanes and obtain the functionalized polysilanes.In this thesis, we have prepared three kinds of organic-substituted polysilanes by using high reactive polymethylsilane(PMS) as precursor: hydrophilic polysilanes, aryl-substituted polysilanes, phenoxy substituted polysilanes. All polysilanes were characterized by FT-IR,’H-NMR, GPC, UV, FL and TG, providing the molecular composition and structure, spectroscopic properties, stability and so on. The aryl-substituted polysilanes could be doped to study their semi-conductor properties.Two kinds of hydrophilic polysilanes, polymethyl(1-propionic acidyl)silane(Aa-PS)and polymethyl(1-undecylic acidyl)silane(Ua-PS)were synthesized by the hydrosilylation of two kinds of unsaturated aliphatic acid, acrylic acid and10-Undecylenic acid with PMS use2,2’-Azobisisbutyronitrile(AIBN)as catalyst. Both modified products show complete solubility in ethanol and diluents sodium hydroxide solutions.The stability of Aa-PS and Ua-PS are much better than PMS,and Ua-PS can stay stable in the air atmosphere for a long time. A red shift of16nm and30nm of maximum absorption wavelength is observed in UV curve of Aa-PS and Ua-PS which from296nm and310nm to280nm.Aryl-substituted polysilanes were prepared by a two step reaction. First, PMS was reacted with carbon tetrachloride for a long time in mild condition to prepare polychloromethylsilane (PCMS). Second, PCMS was reacted with Aryl Grignard reagent. Two Aryl-substituted polysilanes, polymethylphenylsilane (PMPS) and polymethyl(methoxyphenyl)silane (PMMS), were obtained in this paper. Both of the Aryl-substituted polysilanes possess outstanding thermal stability and excellent electronic and optical properties. The maximum UV absorption peak is306nm and312nm, respectively. The FL spectrum chacterization shows that PMPS and PMMS have two fluorescence emitting peaks. As same as PMS, their maximum emission peak in the ultraviolet region is357nm. Their maximum emission peaks in the visible region are420nm and465nm. The conductivity of aryl-substituted polysilane could be as high as10-5S/cm in the range of semiconductor after being doped with iodine. The electronic properties of the main chain are influenced by the electron donating groups, which results a red-shift of FL absorption band and promotion of conductivity.Phenoxy substituting polysilanes, polymethylphenoxysilane (PMPOS) was realized from PCMS and phenol using triethylamine as acid binding agent. It shows excellent optical properties. The maximum UV absorption peak is345nm. The maximum fluorescence emission peak is452nm.All of the modified polysilanes have good solubility in common organic solvents, outstanding performance in process and excellent thermal stability. Ua-PS may have potential applications in the field of Langmuir-Blogdett film and self-assemble macromolecular because of the long side hydrophilic chains. PMPS and PMMS may have potential applications in the preparation of photoelectronic materials. PMPOS is expected to be applied in optical devices due to its excellent spectral properties.