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Phase Separation in Styrenic Polymer Solutions Studied by Spectroscopy

Author: ZhengXinDan
Tutor: ChenXuDong
School: Sun Yat-sen University
Course: Polymer Chemistry and Physics
Keywords: Phase separation Topology Chain entanglement Micellization Conformational transition behavior
CLC: O631.3
Type: Master's thesis
Year: 2010
Downloads: 35
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Abstract

Over the years, the phase separation behavior of polymer solution has been a lot of research attention. Research interests include the molecular weight, solvent effect, the penetration of the polymer, the cyclization reaction kinetics, and so on. Generally speaking, the changes in the chain structure may often lead to a completely different nature of the polymer solution. For example, compared to the equivalent molar mass linear polymer, a high degree of branching of the polymer is usually have lower solution and melt viscosity. Compared with the linear polymer, a high degree of branching of the polymer due to the end of the functional group having a high concentration, thus making the structure is limited, resulting in a very different chemical and physical properties. Therefore, it is very necessary to understand the impact of this topological chain structure of the polymer solution properties. For now, however, few studies have reported on the phase separation of polymer topology chain structure of the solution. In this paper, the authors used the intrinsic fluorescence spectrometry and light scattering studies of macromolecules (including ABA block polymers with different topologies, the hyperbranched structure) chain movement and its phase separation behavior, the main conclusions summarized as follows: (1) through an elastic light scattering intensity variation with temperature, the phase separation process of the PE/PS/CHCl3 solution can be divided into three stages: nucleation - growth spinodal separation and the formation of precipitates. By fluorescence spectroscopy, and further describes the aggregation behavior of the PS in the phase separation process in the chain. By dynamic light scattering and static light scattering, three different molecular weights of the hyperbranched polyethylene has a similar topology. We believe that the branched chain entanglement exists, resulting in three molecular weight hyperbranched polyethylene and polystyrene blends phase separation results different. With PS molecular weight increases, the greater the radius of the PS chain, making it more difficult to enter the voids of the PE, thereby PS molecular weight increases, and the PE worse compatibility. (2) SEBS micellization process in the S-band selective solvent dichloromethane, steady-state fluorescence and scattering methods found that the macromolecular chains movement there are three stages of change. Steven-Ban equations, stage II and stage III excimer formation activation energy is E ae (II) = 22.6 kJ / mol, E the ae (III) = 16.7 kJ / mol. The transient fluorescence results showed that the wavelengths greater than 320nm the monomer peak excimer peak can be ignored, while the the macromolecular chains excimer fluorescence lifetime decreases with decreasing temperature. Molecular chains within excimer fluorescence decay according to the Arrhenius equation, the activation energy E aτ = -8.3 kJ / mol. ΔH o of the SEBS / dichloromethane system micellization process -639.9 kJ / mol, 305K under ΔG o and ΔS o were -29.8 kJ / mol and -2.0 kJ / mol, ΔG o 285 K and CMC were -69.9 kJ / mol and 2.3 × 10-11 g / ml. (3) SEBS the micellization process EB segment selective solvent, n-hexane / cyclohexane (3/1), dynamic light scattering and fluorescence method are able to monitor very clearly four changes to the movement of the macromolecular chain stage. Interestingly, the PEB segment close to and away from the PS has a different ability to display a different conformational changes in behavior in the micellization process. By Steven-Ban equations obtained two excimer formation activation energy: E ae (II) = -3.0 kJ / mol, E ae (IV) = 6.7 kJ / mol. Obtained by the Arrhenius equation, the PEB segment aggregation process away from the PS excimer fluorescence decay activation energy E aτ = - 9.9 kJ / mol.

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