The corresponding growth process generally involves decomposition of the solids to hydrocarbon gases followed by their adsorption onto metallic substrates (e.g. Cu). The Cu foil substrate was also discovered to facilitate the orientation of aromatic moieties during the carbonization process of PI. Since approx. 50% of the original amount of PAA was found to remain at 1000°C, thermally stable polymers can reduce the amount of starting material required to produce high-quality films of graphene.
While the synthesis method of PPX and PPV polymers has been studied, there have been few examples of the attached group on ethylene and vinylene backbone. Furthermore, FT-IR and GC-MS data were investigated to support the structure of bibenzyl and stilbene type dimer. As previously studied, 1H NMR and FT-IR determined the structure of PPX, BrPPX and PPV.
37 Figure 3.7: (a) 13C NMR spectra recorded dehydrohalogenation of TEA-treated BrPPX-2a (CDCl3, with resolution, no NOE, relaxation time = 10 s). b) UV-vis spectra recorded in DMF for BrPPX-2a to PPV-2a. 38 Figure 3.8: (a) Scheme of the alkyne-azide click reaction (b) 1H NMR spectra recorded by PPX-2e (black) and after the click reaction (red) (c) FT-IR recorded by PPX-2e (black) and after click reaction.. b) UV-vis recorded for PPX-2i in DCM solution at 348 nm after UV and visible light cycles.
Introduction
- Engineering plastics from aromatic polymers
- Carbon-carbon bond formation with various condition
- Saturated aromatic polymer – poly(p-xylylene) (PPX)
- Unsaturated aromatic polymer – poly(p-phenylene vinylene) (PPV)
- Contents of Dissertation
Most of the polymers have an aromatic ring in their backbone forming a rigid chain to reduce chain flexibility, terminated with high glass transition temperature (Tg). Wurtz coupling is one of the oldest coupling methods in which a new carbon-carbon bond was given by the reaction of aryl and alkyl halides treated to sodium metal. The proposed mechanism for Wurtz coupling is the formation of organosodium via halogen–metal exchange and formation of a new carbon–carbon bond with the displacement of the halide in an SN2 reaction (Scheme 1.3).
They use the chemical vapor deposition (CVD) method, one of the promising methods for the synthesis of PPX and described in Scheme 1.6. In addition, direct laser writing of the barrelene copolymers obtained by aromatization followed PPV, suitable material for lithographic application. Although functionalized PPX and PPV polymers were studied, there were few examples of the attached group on the ethylene and vinylene backbone.
We also explore the polymerization and structure of the resulting polymers, as well as their underlying polymerization mechanism. Furthermore, we explore halogenated PPX, which is a precursor polymer of PPV, and discuss the modification of the earlier “Gilch” method.
Synthesis of heterocyclic polyimide and usage of the solid source as a graphene synthesis
- Introduction
- Results and Discussions
- Conclusions
- Experimental Method & Materials
- Acknowledgements
As shown in Figure 2.1(b), PAAs exhibit a weight loss around 200℃, which was the dehydration of the cyclization to the imide ring of the amide group. Using LB techniques, monolayers of PAAs and PMMA salts were deposited on copper foils109-110 and these surface and thickness characterizations were performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) (Figure H.1). ; the corresponding isotherms of surface pressure and area (Π-A) of the bottom of the LB are shown in Figure H.2. Then, efforts were directed to determine the thickness of the polymer film that affected the graphene conversion, and different film layers were deposited on the Cu surface by the LB method.
As shown in Figure C.4, an inspection of the temperature-dependent Raman spectra recorded for BTDA-PDA on Cu foils revealed that the size of the graphitic domains (crystallites) increased during the carbonization process, consistent with the mechanism described above. On the other hand, the thicker PAA films (i.e. those consisting of three or five layers) may not have resulted in the formation of high quality graphene upon annealing because the upper regimes of the carbonized materials were not in contact with the Cu surface. and therefore structural realignments are less likely to occur. Yellow and gray lines represent PAA precursors. a) The change in weight as a function of temperature.
Graphene formation from (b) PAA and (c) PMMA according to the corresponding temperature of the graph shown above. Finally, we discuss how the quality of the PI-GR products depended on the type of PI precursor used.
Synthesis of aromatic polymers (PPX, BrPPX and PPV) and deciphering their structure . 25
Results and Discussions
Conclusions
Experimental Method & Materials
Acknowledgements
General scheme of synthesis PPV from Gilch and Wessling route
Vansheĭdt, A.; Mel'Nikova, E.; Krakowjak, M.; Kuhareva, L.; Gladkovskiĭ, G., Synthesis and properties of crystalline polymers of the type poly-p-xylenes and polyphenylene methyl derivatives.
Synthesis of PPV using transition metal-catalyzed coupling reaction (Heck, Suzuki,
Synthesis of PPV through ring-opening metathesis polymerization
In Chapter 2, various types of ultrathin polyimide film were prepared by the reaction of dianhydride and diamine after the addition of poly(amic acid) salt produced from alkylamine. After the polymer solution was spread in the trough and several layers of it, the film was deposited on the substrate by the Langmuir-Blodgett method and further heat treatment provided polyimide film. Then, carbonization of the polyimide film was performed under vacuum in a CVD system to obtain graphene on the substrate from a solid polymer source.
Functionalized derivatives of PPX and PPV were envisioned through the incorporation of substrates containing alkene, alkyne, benzyl, cholesterol, azo group ester or carboxylic acid groups. Characterization of the converted film was performed with FT-IR spectroscopy, as aromatic PIs become infusible and insoluble. The key change of FT-IR was the disappearance of C-N bond peak observed at 1405 cm-1 and carbonyl C=O peak observed at 1662 and 1722 cm-1 assigned to corresponding carboxylic acid and amide.
Then the appearance of a new peak at 1359 cm-1 assigned to the C-N-C imide bond and carbonyl C=O for imide peak observed at 1720 and 1778 cm-1 respectively. 1 disappears after imidization indicated that the dehydration occurred during imidization. Furthermore, there was no change of C=C bond of aromatic ring observed at 1513 cm-1 before and after imidization.
The synthesis of PAA and its salt followed the method described in the literature9, 108-110 and was summarized in Scheme 2.1. In order to investigate the thermal stability of PAA and PI, the weight change during the thermal annealing process was monitored by TGA up to 1000 ℃ with a heating rate of 100 ℃ min-1 in an Ar atmosphere, which was a similar condition for performing the heating process. carbonization into graphene. Although some wrinkles were observed, they may have originated from the difference in the coefficient of thermal expansion between copper and graphene.81 The HR-TEM image shown in Figure 2.2(c) together with the fast Fourier transform image (inset) shows that high-quality graphene was created.
Raman spectra measured by layer characterization of graphene and the sharp peaks of the G and 2D bands with the high 2D/G ratio (2.25) and the lack of a D band suggested that the resulting graphene was monolayer with a defect-free surface . On the other hand, when monolayer PMMA was used as solid source, resulting graphene showed strong and broad D and G bands with a weak 2D band indicating the incomplete formation of graphene.114-115 Moreover, PMDA-based PAA produced a lower quality of graphene than BTDA based PAA from these Raman data Figure 2.2(d). Notably, the use of three layers of PAA produced graphene that was of higher quality than that obtained from five layers of PAA.
A difference between using monolayer versus bilayer of PAA as precursors is that the former provided a surface approximately 92% covered with graphene where the latter resulted in essentially complete coverage. The as-prepared monolayers of PAA dehydrate upon heating to 240 ℃ and the resulting PIs undergo carbonization together with atomic rearrangement and fusion upon further heat treatment.98, 116 It is known that reorientation of aromatic moieties occurs in confined spaces during carbonization such species are not precisely in line not Meanwhile, the substrate can help the conversion of such aromatic intermediates to graphene by reducing the activation barriers for dehydrogenation and nucleation due to the strong interactions formed between Cu and the aromatic moieties in PI As noted in the conclusions derived from the TGA data described above, about 50% of the initial amount of PAA remained after heating the material to 1000.
Proposed mechanism of graphene growth on Cu substrates from various polymer
From the Raman spectra shown in Figure 2.2(d), we concluded that the PI-GRs grown from the BTDA-based PIs were of higher quality than those prepared from the PMDA-based PIs. In support of this conclusion, annealing PMDA-based PIs at 450 ℃ improved the quality of the formed graphene (Figure C.5). Monolayers of PAA were transformed in situ into thermally stable PIs when heated to 240 ℃ and then into layers of graphene when exposed to temperatures of approximately 1000 ℃ on Cu foils.
The corresponding conversion mechanism was investigated and appears to consist of the rearrangement of aromatic species arising from the PIs during the carbonization process along with orientational assistance from the catalytically active Cu substrate. Collectively, the methodology described herein increases atomic efficiency to prepare high quality sheets of graphene from solid precursors, especially compared to methods using PMMA or other solid sources. Before deposition, the Cu substrate was treated with an oxygen plasma for 10 minutes to make the surface hydrophilic.
The sample was then cooled on removal from the furnace and transferred to a Si substrate prepared by depositing 300 nm SiO2 on a Cu substrate followed by etching with ammonia persulfate (0.1 M). I acknowledge the contributions of Jo, Hye Jin in the synthesis and analysis of graphene and also grateful to Lim, Hyunseob, Yoon, Seong In, C.W.
Redox reaction and potential of Tetrakis(dimethyl amino) ethylene
Preparation of PPX, BrPPX and PPV from α-bromo xylene derivatives with organic
Synthesis of dialkyl 2,2’-(1,4-phenylene)bis(2-bromoacetate)
The 5% decomposition temperature (Td5) was recorded for PPXs higher than 300 ℃ that polymer exhibited great thermal stability, while those of PPVs were obtained at temperature higher than 220 ℃ relatively low PPX- ve that can from the remaining BrPPX, especially gave the less soluble side chain methyl PPV-2a (Figure 3.6).
