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The Application Of Two-Dimensional Correlation Spectroscopy On The Study Of Some Representative Polymeric Systems

Posted on:2007-12-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y ShenFull Text:PDF
GTID:1101360212484288Subject:Polymer Chemistry and Physics
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This thesis centers on the application of two-dimensional (2D) correlation spectroscopy on the study of some representative polymeric systems. 2D correlation spectroscopy was proposed by Noda in 1986. And in 1993, it had been developed as "Generalized 2D Correlation Spectroscopy". Compared with conventional one-dimensional (ID) spectroscopy, 2D correlation spectroscopy owns the high resolution and it can distinguish the motion sequential order of the different functionalities of polymers. Thus, it is often looked upon as a useful initial probing tool to aid in the analysis of complex ID spectra and has received wide applications in the different fields. This thesis lays attention on the study of the perturbation-based structural/conformational changes of polymers by 2D correlation spectroscopy. The information can help us set up the relationships between the structure and property of polymers.The thesis contains six chapters. Chapter one is the introduction of the whole research work. In chapter two, three different polymers: polythiophene (PTh), poly (3-chlorothiophene) (PCTh) and poly(N-vinylcarbazole) Cr(CO)3 (PVKC) have been studied. Firstly, we have studied the thermal-based structural changes of PTh and PCTh using 2D Raman correlation spectroscopy. In doping PTh, the thiophene rings in the neutral species are connected by C-C bonds. Thus, it is easier for the neutral species to adjust the conformation under the thermal perturbation. On the other hand, the thiophene rings in the oxidized species are connected by C=C bonds. Lowering the temperature cannot easily change the conformation of the oxidized species. Thus, the oxidized species are not very sensitive to the temperature in the cooling process. However, in the heating process, the oxidized species are generally reduced to the neutral species. The occurrence of the structural change is due to that positively charged segments in PCTh are susceptible to a nucleophilic attack by oxygen or water and the increase of the temperature seems to accelerate the reaction processes, leading to the reduction of the oxidized species finally.On the basis of this work, we further investigate the thermal-based structural change of PVKC in the heating process using 2D FTIR correlation spectroscopy. The Tg of PVKC (75-95℃) is confirmed according to the result of the quantitative analysis, which is in accordance with the result of DSC experiment. A tentative assignment of carbonyl bands is also made using the information shown in the 2D spectra. More importantly, the detailed analysis show that the chromium tricarbonyl group may lose its bond with the aromatic ring in the ligand after 140°C, leading to the loss of the optical property.In chapter three, we have studied the mechanism of the liquid-crystalline (LC) phase development of a representative mesogen-jacketed liquid crystal polymer, poly{2,5-bis[(4-methoxyphenyl) oxycarbonyljstyrene} (PMPCS) using 2D FTIR correlation spectroscopy. The phase transition range 120°C-160°C is examined according to the result of the quantitative analysis. 2D correlation analysis is performed on the temperature-dependent IR spectra to probe the sequential order of changes in the different functionalities of PMPCS. The results show that both the backbone and side chain contribute to the LC phase development, although the functional group responsible for the formation of liquid-crystalline phase is located only in the side chain.Before the phase transition, the conformational change of individual side chains occurs sooner than that of the backbone due to the larger freedom of the side chains. After the phase transition, however, the readjustment of still somewhat mobile backbone occurs before the ordered, rigid, and mutually interacting side chains. That is, phase transition leading to the LC phase formation brings in a new cooperative restriction of motions to the segments. In addition, the earlier motion of the functionalities in disordered conformational state compared to those with ordered conformation under the thermal perturbation probably explains the relative ease of development of LC phase in PMPCS.In chapter four, the fabrication and denudation process of (poly(3-thiophene acetic acid) / poly(4-vinylpyridine))n ((PTAA/ P4VP)n) layer-by-layer (LBL) films has been studied by 2D UV-vis correlation spectroscopy. The UV-vis spectra are used to do the 2D correlation analysis. The results show that PTAA has a faster adsorption rate than P4VP. Combining the driving force of (PTAA/ P4VP)n multilayers, we have proposed a model to describe the construction of the multilayer film. P4VP chaintakes advantage of its flexible property to entangle around the rigid backbone of PTAA, which largely shortens the distance between the neighboring PTAA chains. Thus, it is reasonably proposed that there exist hydrogen bonds between the neighboring PTAA chains. Accordingly, the borderline can only be distinguished between the bilayers and there is no clear borderline between PTAA and P4VP in each bilayer of the multilayer films.As we know, hydrogen bonds are sensitive to pH value. We have further investigated the influence of the acid and alkaline aqueous solutions to the structure of multilayers using 2D UV-vis spectroscopy. In the alkaline aqueous solution, PTAA is ionized and two different types of hydrogen bonds (I: hydrogen bonds between PTAA and P4VP chains; II: hydrogen bonds between PTAA and PTAA chains) are destroyed, leading to the rapid deconstruction of the multilayers. In the acidic aqueous solution, the protonation of P4VP only destroys the hydrogen bonds between PTAA and P4VP chains. On the other hand, the hydrogen bonds between PTAA and PTAA chains still exist because PTAA dissociates slightly at low pH value. Thus, the rate of the deconstruction in the acidic solutions is much slower compared with that in the alkaline solutions.In a word, the information shown in the 2D UV-vis spectra not only helps us set up a model of the construction process, but also provides a reasonable explanation of the change of the components in the deconstruction process. This work proves the feasibility of 2D UV-vis spectroscopic technique.In chapter five, we have studied the dynamic diffusion behavior of water in the polymeric membranes using 2D ATR-FTIR correlation spectroscopy. Two different polymeric materials: poly(4'4-oxydiphenylene pyromellitimide) (PMDA-ODA)/silica nanocomposite (PISA) and polypropylene (PP) have been studied. The dynamic ID ATR-FTIR spectra were firstly recorded and then we apply 2D correlation analysis to gain the information about the state of water molecules and the dynamic diffusion behavior.Firstly, we take advantage of the high resolution of 2D spectroscopy to separate the different states of water molecules according to the different strength of hydrogen bonds. In PP matrix, water molecules have no interaction with PP network because PP is a hydrophobic material. Thus, the hydrogen bonds only exist between the water molecules. However, in PISA matrix, water molecules have interaction with PISAnetwork because PISA is a hydrophilic material. Thus, the hydrogen bonds refer to several formations: H-bonding formed between the water molecules, H-bonding formed between water molecule and silicic acid (residues), H-bonding formed between water molecule and PI system.Secondly, we distinguish the motion sequential order of the different states of water molecules according to the signals of 2D cross-peaks. The study shows that the volume of the water clusters influences the diffusion rate, while the property of the polymer influences the amounts and diffusion coefficient of the water molecules.Chapter six is the conclusion to the whole research work. The main technique used in all the work is the 2D correlation spectroscopy. Firstly, we record the dynamic spectra of the polymeric materials. Secondly, we take advantage of the high resolution of 2D spectroscopy to separate the weak bands and originally overlapped bands in the ID spectra. Accordingly, we can distinguish the groups in different states and conformations. Thirdly, 2D correlation analysis can often simplify spectral features corresponding to various inter- and intramolecular interactions, so we can elucidate the relationships between different groups and further search the related mechanism.On the other hand, in this thesis, we apply the 2D correlation analysis to different ID spectroscopies. The most useful research technique is the 2D FTIR correlation spectroscopy. And in this thesis, we have applied this method to the study of PVKC and PMPCS. Additionally, we have applied 2D Raman correlation spectroscopy to the study of conducting polymers. More importantly, we also tried the 2D UV-vis correlation spectroscopy in one chapter. As for our knowledge, the research work centering on the application of 2D UV-vis correlation spectroscopy in the study of mechanism remains limited. The work here not only verifies the feasibility of 2D UV-vis correlation spectroscopy, but also opens the application fields of it.
Keywords/Search Tags:two-dimensional correlation spectroscopy, polymer, structural change, mechanism
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