Synthesis Of Functional Polyacetylenes And Their Hybridization With Carbon Nanotubes

Carbon nanotubes (CNTs) are of great interest in scientific research and technological innovation due to their unique nanostructures and novel properties. Particularly, their remarkable electronic and optical properties make them promising for such applications as nanosensors, nanoelectrodes, quantum wires, molecular diodes, and photoelectrochemical devices. In many cases, however, due to the strong hydrophobicity,Ï€-Ï€stacking, van der Waals attraction between the carbon nanotubes along with their ultrahigh molecular weight, CNTs are bounding together and insoluble in most common solvents. The insolubility greatly limits the applications of the carbon nanotubes to the real world.Two approaches, i.e., covalent and noncovalent functionalizations, have been used to improve the macroscopic processability of CNTs. The noncovalent approach can confer new properties on the CNTs without destroying the electronic conjugation of their curled graphene sheets. Among all the routes for the noncovalent functionalization, wrapping CNTs in conjugated polymers is an attractive one. It is well known that conjugated polymers with macroscopic solubility and electrical semiconductivity have the potential to find high-tech applications in photoelectronic devices such as light-emitting diodes, photovoltaic cells, and field-effect transistors. Wrapping CNTs in such polymers are expected to endow the CNTs with macroscopic processability and new photoelectronic properties. On the other hand, CNTs may help enhance charge transport, mechanical strength, and chemical stability of the conjugated polymers.Polyacetylene is a prototypical conjugated polymer. The discovery of metallic conductivity of its doped forms has opened up a new area of research on "synthetic metals" or "plastic electronics". Replacement of the hydrogen atoms in the repeat units of PA with appropriate pendants endows the polymers with such functional properties as photoconductivity, luminescence, mesomorphism, optical activity, gas permeability, biocompatibility and cytophilicity.This thesis attempt to fabricate functional polyacetylenes/CNTs hybrids in the hope of deriving a series of processable polyacetylenes/CNTs conjugates and combining the advantages of two components and generating new charming properties through a noncovalent way. Based on this concept, pyrene- and ferrocene-containing polyphenylacetylenes (PPAs) were synthesized. These derivatives are luminescent or redox-active. What's more, as expected, they can be used as good dispersants for CNTs. The solubilities of CNTs functionalized by these polymers are much higher than those modified by their counterpart monomers, exhibiting an obvious "polymer effect". The PPAs/CNTs hybrids show good stability, film forming ability and re-dispersion capacity. Meanwhile, effective photo-induced charge transfer and electron transfer are observed in these systems. The hybrids are promising to be applied in the fields of photovoltaic materials and devices.Unique beads-on-string morphologies are observed in pyrene-containing PPAs/CNTs hybrids. Through morphological and photo-physical studies, it is found that the strong interactions among the polymer chains induced self-aggregation and theÏ€-Ï€interaction between polymer chains and CNTs, which should be ascribed to the unique morphology.To further study the mechanism for solubilization of CNTs, some poly(l-alkyne)s (PAs) with ferrocene or pyrene pendants were synthesized. As comparison, poly(l-alkyne) without any aromatic motifs was also synthesized. It is found the latter polymer hardly contributes to the solubilization of CNTs, while the former polymers behave well. It suggests that sole polyalkyne main chain has no solvating power to CNTs, and the aromatic pendants play key roles in solubilizing CNTs. A notable "polymer effect" of the solvation power is also observed in this system. The discovery of different solvating powers of varied PPAs and PAs to CNTs, and the illumination of the mechanism are helpful for the design and synthesis of new functional polyacetylenes which can be used to generate soluble polyacetylenes/CNTs hybrids.Besides the monosubstituted polyacetylenes, diphenylacetylene derivatives containing reactive vinyl groups and polar ester functionality were successfully polymerized. The WCl₆-Ph₄Sn mixture can selectively catalyze the metathesis polymerization of the acetylenic triple bonds and leave the vinyl bonds undamaged. The solutions and films of the functionalized disubstituted PAs emit efficient green light upon photoexcitation. The photopolymerizability of the (meth)acrylic pendants of the polymers allows their films to be patterned into fluorescent images. A unique and useful aggregation enhanced emission (AEE) phenomenon is observed in the light emission processes of the polymers in the THF/water mixtures, owing to the restriction of the intramolecular rotations by the aggregate formation.Then some disubstituted polyacetylenes (DPAs) were used as the dispersants to disperse CNTs in common organic solvents. It is exciting that all of the polymers used are quite effective in solubilizing CNTs. All the DPAs/CNTs hybrids show the characteristic emission of the DPAs. However, the quantum yield (Φ_F) of different hybrid systems exhibit varying trends when compared with those of their pure polymer solutions. Generally, there are two factors affecting the change ofΦ_F. One is the electron and/or energy transfer between the polymer chains and CNTs, which will decrease the Of and the other is the AEE of the polymer chains aggregated nearby the CNTs, which will increase theΦ_F of the system.Unprecedentedly and successfully, direct polymerizations of acetylenic monomers bearing -COOH, -NO₂, and -NH₂ pendants using Rh complexes were realized. And it updated the traditional concept that -COOH containing acetylenic monomers can not be polymerized by Rh based catalysts. Through polymer reactions with NaOH and HCl solutions, -COOH and -NH₂ containing polyacetylenes were converted to water soluble polymers. Using them as dispersants, we obtained water soluble polyacetylenes/CNTs functional hybrids. Then these hybrids were decorated with metal and semiconductor nanoparticles. The successful preparation of the three component hybrids paves the way for the potential applications of these materials in catalysis, nanotechnology, electronic nanodevices and so on.