Functional Modification Of Polymethylsilane

Polysilanes have recently attracted considerable attention due to their unusualelectronic and photophysical properties as well as their potential applications inceramics, in microlithography, as photoconducting polymers, as nonlinear opticalmaterials and so on. The unique electronic and photophysical properties of polysilanesare derived from the extensive delocalization ofσ-electrons along the silicon backboneand are extremely sensitive to the nature of the substituents attached to the polymerbackbone. The introduction of functional organic groups into polysilane by directpolymerization of funcionalized monomers is limited by the vigorous conditionsemployed in the condensation reaction. Functional modification of preformed polysilaneis a smart strategy to overcome this limitation and prepare polysilane high polymers.In this study, we synthesized a high reactive polymer, polymethylsilane (PMS)which was used as a modification template to prepare two kinds of organic-substitutedpolysilanes: amphiphilic polysilane andσ-πconjugated polysilane. The polymercomposition, the molecular structure, the molecular weight, the stability, the spectrumproperties, and other properties of the polysilanes were characterized by FT-IR,1H-NMR, GPC, UV, TGA, FL and so on.PMS is often used as a kind of SiC ceramic presurcor due to its stoichiometric ratioof Si:C. On the other hand, PMS is a very good modification template to preparefunctional polysilane for its plenty of reactive Si-H bonds. In this work, PMS wassynthesized by Wurtz coupling reaction from methylhydrodichlosilane with sodium.The chemical composition of the PMS is [Si(CH3)2]0.03[(Si(CH3)H]0.66[Si(CH3)]0.31. Thenumber average molecular weight is 441, and the weight average molecular weight is1089 charcterized by GPC (Polystyrene Standard, similarly hereinafter).Two kinds of amphiphilic polysilanes, polymethyl(1-propionic acidyl)silane(Aa-PS) and polymethyl(1-undecylic acidyl)silane (Ua-PS) were synthesized by thehydrosilylation of two kinds of unsaturated aliphatic acid, acrylic acid and10-Undecylenic acid with PMS using 2, 2'-Azobisisbutyronitrile (AIBN) as catalyst,respectively. The reaction time effecting on the degree of hydrosilylation and theresulted polymer structer was studied and the best reaction time was 12h. The reactionmechanism was also studies, another competition reaction mechanism was supposed.The resulted Ua-PS was characterized as the structure[Si(CH3)2]0.03[Si(CH3)R]0.40[Si(CH3)H]0.26[Si(CH3)]0.31{R = (CH2)10COOH)} with thenumber average molecular weight 4428 and the weight average molecular weight 5157.Ua-PS and Aa-Ps became amphiphilic polymers while PMS was a hydrophobilcpolymer. The UVλmax of Ua-PS and Aa-PS had a red shift from 280nm to 300nm compared to PMS. Ua-PS showed a double peak in the UV spectrum, which might bedue to its special conformation. The stability of Ua-PS and Aa-PS was much better thanPMS, and Ua-Ps could stay stable in the air atmosphere at room temperature.σ-πconjugated polysilane was synthesized by a two step reaction. First, PMS wasreacted with CCl4 in the mild condition to prepare polymethylchlorosilane (PCMS).Second, PCMS was reacted with phenyl Grignard reagent to preparepolymethylphenylsilane (PMPS). The resulted PMPS was characterized as the structure[Si(CH3)2]0.03[Si(CH3)Ph]0.40[Si(CH3)(n-Bu)]0.05[Si(CH3)H]0.21[Si(CH3)]0.31 with thenumber average molecular weight 3081 and the weight average molecular weight 8005.The UVλmax of PMPS had a red shift from 280nm to 305nm compared to PMS. Thestability of PMPS was much better than PMS both in ambient temperature and elevatedtemperature in inner atomosphere. The FL spectrum chacterization showed that PMPShad two fluorescence emitting peaks with theλmax 360nm in the ultraviolet region andtheλmax 420nm in the visible region.Both the two kinds of modified polysilane showed good solubility in commonorganic solvents. They were very stable in the air at room temperature. Ua-PS may havepotential applications in the field of Langmuir-Blogdett film and macromolecularassemblies due to the long side hydrophilic chains, and PMPS may have potentialapplications in the preparation of photoelectronic materials.