| Summary: | 博士 === 國立臺灣科技大學 === 纖維及高分子工程研究所 === 88 === The degree of interaction between polymer and solvent much depend on the molecular structures of each component. The polymer chains exhibit relatively extended conformations in a good solvent system, but they are collapsed in a poor solvent system. Generally, the strong intermolecular charge rearrangement and strong dipole-dipole interaction directly generate the attractive interaction between each component. In this thesis, the degree of the polymer-solvent interaction in the polyvinyl chloride (PVC) solutions can be estimated by the static light scattering and viscometric methods. The -temperature in PVC/ tetrahydrofuran (THF) system is close to 0℃ which is much lower than that in the PVC/ morpholine (MOR) (56℃) and PVC/ dioxane (DOA) (70℃) systems. The results clearly predict that the degree of molecular interaction is PVC/THF > PVC/MOR > PVC/DOA in order. In PVC/THF system, it is more difficult to form gel; the critical gel concentrations are 1.5 gdL-1 and 2.2 gdL-1, respectively, for PVC/DOA and PVC/MOR systems. Then, it could illustrate that PVC/DOA gels are more heterogeneous through the light scattering and pulsed NMR measurements, but the solutions are more homogeneous in PVC/THF system. In the PVC/ nitrobenzene (NrBz) and PVC/ chlorobenzene (ClBz) systems, the affinity of NrBz to PVC is higher than that of ClBz. The value for PVC/ClBz solution is only 1.7 gdL-1, but for the PVC/NrBz solution it is much higher than 6 gdL-1. The CPMG decaying signals from pulsed NMR measurement of the PVC gels could be decomposed into three components, reflecting respectively the proton mobility in the junction zone, in the polymer-rich phase and in the solvent-rich phase of the gel network. The solutions began to show the fraction of junction zones at the PVC concentration above 1.5 gdL-1 and 6 gdL-1, respectively, in the PVC/ClBz and PVC/NrBz solutions, while the formation of the junction zones could interconnect the polymer chains to be a three-dimensional network structure macro-domain. Therefore, the result indicates that the PVC/ClBz solution has better gelation ability. Through the discussion of the diffusion property of the solvent molecules, we could clearly verify that the gel network of PVC/ClBz gels is denser than that of PVC/NrBz gels.
In the PVC/Poly(methly methacrylate) (PMMA)/solvent ternary system, the interaction between PVC and PMMA could influence the viscosity behavior of the polymer solutions. In PVC/PMMA/tetrahydrofuran (THF) solution, the tighter PMMA coils in solution could be regarded as islands; the extended PMMA coil could be regarded as see. At lower PMMA fraction, the sea-island heterogeneous structure directly reflects lower PVC/PMMA miscibility. At PMMA weight fraction higher than 0.7, the PVC/PMMA mixtures are relatively miscible and give more homogeneous polymer solutions. In PVC/PMMA/N,N-dimethylformamide (DMF) solution, two polymers really present extended conformations, which enhance the interaction with each other. Actually, it exhibits higher miscibility between PVC and PMMA when the PMMA weight fraction equal to 0.5.
The intermolecular interaction discloses more complex in a polymer/mixed solvent system, two solvent molecules own competition for attack a polymer segment. In general, the polymer segments preferentially adsorbed with the good solvent molecules. In polyvinyl alcohol (PVA)/N-methyl-2-pyrrolidone (NMP)/water system, one NMP molecule could bind with two water molecules for formation of strong NMP(water)2 ter-solvency complex. Then, the formation of complex is found to significantly affect the polymer preferential adsorption phenomenon. At the NMP volume fraction <0.73, the PVA chains preferentially adsorb the water molecules. Owing to lower affinity of water, the contracted PVA coils are formed at this condition. At >0.73, the PVA chains preferentially adsorb NMP, which is a better solvent for PVA, inducing the A2 values rapidly increases. The PVA coils exhibit much extended conformations. Moreover, the theoretical values of preferential adsorption coefficient, , obtained from two Read formalisms are in poor agreement with the experimental results, for without consider the formation of solvent complex. Then, we try to expand the Read formalism with considering the complex effect, then the calculating data more conforms to the experimental result.
In PVA/ dimethyl sulfoxide (DMSO)/water system, the solution could form hydrogen bonded DMSO(water)2 complexes, involving one DMSO and two water molecules. The complex formation directly induces PVA chains preferentially adsorb water molecules at DMSO mole fraction, , lower than 0.33, but preferentially adsorb DMSO molecules at >0.33. Indeed, the formation of DMSO(water)2 complexes could increase the tendency for liquid-liquid phase separation and aggregation of PVA chains in solution. At ~0.33, both DMSO and water molecules have large tendency to leave PVA chains domains, this desorption phenomenon reflect the rapid gelation rate and liquid-liquid phase separation.
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