Synthesis, Optoelectronic Properties, And Morphology Of Triphenylamine-Functionalized Polyacetylene

Nowadays, metathesis cyclopolymerization (MCP) as a highly novel method has been widely used in the syntheses and investigation of various functionalized polyacetylene (PA) derivatives, such as liquid crystal materials and nonlinear materials, however, the research towards both optical and nanomaterials area is relatively rare. Therefore, it is essential to expand the research and application in these fields. After MCP, the PA main chain own a unique microstructure due to the introduction of the cyclic structure and the conjugated double bonds, so, it is possibility to obtain single microstructure of PA by selecting suitable catalyst and monomer. At the same time, introducing various substituents at 4-position of 1,6-heptadiyne monomer could synthesized soluble and functional PAs by MCP. Adjusting the number and size of substituents is to solve the problem of poor solubility and oxidative stability of polymer, and further to promote the properties of polymers.Triphenylamine-functionalized polyacetylene (TPA-PA) is a class of functionalized PA derivatives that TPA moiety was introduced into PA backbone, which were found to have the properties of photoluminescence, electrochromism, gas permeability, and dissolution of multiwalled carbon nanotube since 2006. Reported TPA-PAs were obtained from the diphenylacetylene derivatives polymerized with several Rh-, W-, and Mo-based catalysts. Although such methods can also synthesize the PAs with high molecular weight (Mn), relatively long conjugated chain, its application is still limited due to broadpolydispersity index (PDI), irregular microstructure, and instability in air. The third-generation Grubbs catalyst (Ru-Ⅲ) has many advantages, such as high activity, good control and stereoselectivity.When MCP was performed, resultant polymer with high Mn and narrow PDI, and selectively generated a five-membered ring and all-trans microstructure. Therefore, it is envisioned that the MCP of TPA-functional 1,6-heptadiyne monomer by use of Ru-Ⅲ catalyst would generate PA derivatives possessing regular microstructure and excellent properties.In this dissertation, we have designed functional 1,6-heptadiyne monomer bearing one or two pendent TPA groups to obtain PAs with excellent optoelectronic properties and unique nanocylinder morphology via MCP.Changing the number and size of substituent is to obtain polymer with different photoelectric properties, oxidation stability, thermal properties, and self-assembled morphology; the characterization of polymerization behavior, maximum absorption wavelength, and energy bandgap indicated the relationship between the number or size of substituent and the polymerization rules or photoelectric properties. Further investigation on the influence of substituent and polymer properties, such as oxidation stability and self-assemble morphology, was well performed.As an initial attempt, we have designed the mono-substituted TPA-functional 1,6-heptadiyne monomer Ml and MCP was conducted to obtain poly(Ml) with different degree of polymerization. Firstly, The use of NMR and Roman spectroscopy effectively characterize the microstructure of poly(Ml), possessing a five-membered ring structure and all trans-PA. The Mn increased with increasing the ratio of monomer to catalyst, which demonstrated that MCP of Ml in THF proceeded in a good controlled manner by the action of catalyst Ru-Ⅲ. Secondly, poly(Ml) showed excellent solubility in common organic solvents and displayed solvatochromic behavior, the λmax of poly(Ml) shifted in a small region from 591 to 595 nm when the DP sharply increased from 22 to 316, the onset absorption (λonSet) was 680 nm, band gap (Eg) was 1.82 eV, and the fluorescence quantum yield (ΦF) in toluene was 1.4%. On the basis of above results, by changing the number and size of substituent of monomer has been considered. We have synthesized bis-substituted TPA-PA (poly(M2)) and found that it also own all-trans five-membered ring microstructure. Although the DP of poly(M2) was only up to 29, the λmax was red-shifted to 605 nm, and the corresponding λonset was extended to 700 nm, Eg was 1.77 eV, and ΦF was increased to 12.3%, indicatingthat poly(M2) with shorter conjugated chain length has a relatively better optoelectronic properties. Thus, when the polymer own the same microstructure, the number and size of side groupswould determine the properties of polymer.To confirm and gain further understanding on relationship between the number or size of side groups and the properties of polymer, the oxidation stability, thermal properties and morphologyof TPA-PAs have been investigated. Firstly, TPA-PAs have been characterized by IR spectra, and found that the IR spectrum of poly(Ml) showed obvious carbonyl absorption band at 1796 cm-1 after exposed for 3-4 months in air at the room temperature, however, IR spectrum of poly(M2) has almost no change after exposed for 3-4 months. UV-vis spectroscopy in THF is more effective method to characterizethe oxidation stability of PAs, when poly(Ml) was saved in THF solvent, the absorption overall intensity died away after 10 days, by contrast, poly(M2) was extremely stable in THF even prolonged time to 30 days. Secondly, DLS, AFM and TEM results showed that poly(Ml) was loosely aggregated in different solvents, while had no obvious assembly behavior, however, poly(M2) could stably achieved the spontaneously self-assembly of intriguing nanocylinder in different concentrations and solvents. These results further demonstrated that the number and size of side group have an effect on polymer properties. XRD and DSC results show that poly(M1) had a low degree of crystallinityof 14%, whereas poly(M2) was amorphous and the glass transition temperature was up to 130.6 ℃.