Polyurethane/Poly(methyl methacrylate)/Polyaniline composite particles via Miniemulsion Polymerization -Synthesis, Morphology and Property
Date Issued
2006
Date
2006
Author(s)
Li, Chien-Yu
DOI
en-US
Abstract
In this thesis, first of all, the synthesis of high-molecular-weight polyurethane (PU) was prepared successfully by two-step miniemulsion polymerization. Second, PU/PMMA hybrid particles were synthesized and discussed with their morphologies. In addition, by consideration of thermodynamics, the analysis of free energy changes produced the prediction of the preferred-particle morphology. Finally, the conducting composites of PU/polyaniline and PU-PMMA/polyaniline particles were also prepared and characterized.
Utilizing a two-step miniemulsion polymerization, hydrophobic polyurethane dispersions were prepared with co-surfactant, hexadecane (HD) hydrophobe in oil phase and sodium dodecyl sulfate (SDS) in water phase. The first step involved the formation of NCO-terminated prepolymers between isophorone diisocyanates (IPDI) and poly (propylene glycol) (PPG) oligomer in toluene. Next, polyurethane dispersions were produced by a miniemulsion method where an oil phase containing NCO-terminated prepolymers, HD, a chain extender 1,4-butanediol (BD), a cross-linking agent trimethylol propane (TMP), and a catalyst dibutyltin dilaurate (SnDBL) was dispersed in the water phase containing SDS. The influences of experimental parameters, such as ultrasonication time, concentration of SDS and HD, TMP/BD and NCO/OH equivalent ratios on the sizes of miniemulsion droplets and polymer particles, as well as the molecular weight and thermal properties of PU polymer were discussed. Chemical structure of the produced PU polymer was identified by Fourier-transform infrared spectrometer. Molecular weight distribution and average particle size were measured through gel permeation chromatography (GPC) and dynamic light scattering (DLS), respectively. Thermal properties of PU polymer was characterized through differential scanning calorietry (DSC) and thermal gravimetric analysis (TGA). The final morphology of PU particle was also characterized by transmission electron microscope (TEM).
PU/PMMA hybrid particles were synthesized by using the method of two-step miniemulsion polymerization. In the first step, PU prepolymer was synthesized by isophorone diisocyanates (IPDI) and poly (propylene glycol) (PPG) with methyl methacrylate (MMA) as a solvent. Then the oil phase, including the NCO-terminated prepolymer, MMA, hexadecane (HD), a chain extender as 1,4-butanediol (BD) or bisphenol A (BisA), a cross-linking agent trimethylol propane (TMP), and a catalyst dibutyltin dilaurate (SnDBL) is dispersed in the water phase containing SDS. Then the mixtures turn into miniemulsion by ultrasonifying. Two kinds of initiators, BPO and KPS, were applied for the polymerization of MMA. The influences of chain extenders, initiators and PU/PMMA weight ratios on the morphology of PU/PMMA latex particles were investigated. Conversion of MMA was measured and discussed. Particle size and distribution were analyzed by dynamic lighting scattering (DLS) and transmission electron microscope (TEM). Thermal stability of the hybrid particle was characterized through thermal gravimetric analysis (TGA). The cross section morphology of the hybrid particles was also characterized TEM. For BD/BPO and BD/KPS systems, when increasing the load of PU component, PU-rich phase was moved to the outside of hybrid particles. A core-shell structure can be observed. However, for BisA/KPS system, while using hydrophobic bisphenol A as chain extender of PU, the boundary of PMMA and PU phases was not clear. A more homogeneous structure of hybrid particles can be obtained.
In this chapter, the morphology of PU/PMMA hybrid particles prepared by miniemulsion polymerization was predicted through the consideration of their Gibbs free energy changes. Five morphological states of PU/PMMA hybrid particles were proposed and their Gibbs free energy changes were calculated. Before the formation of hybrid particles, the initial state included a monomer mixture of PU prepolymer, MMA, a chain extender, TMP and an initiator, which was in droplets suspended in water containing SDS. Two assumptions were made. First, the densities of all states were the same. Secondly, secondary nucleation of particles was negligible. Thus the size of initial droplet and final particle was unchanged through miniemulsion polymerization. The interfacial tensions were measured by a pendant drop method and were used for calculation. The preferred morphology of PU/PMMA hybrid particle had the minimum value of ΔGphase. Different NCO/OH ratios of PU and initiators of MMA were used to study the morphological change of PU/PMMA hybrid particles. When BD was used as the chain extender of PU, the hybrid particles showed the PU-rich phase as the shell and PMMA-rich as the core. When incorporating bisphenol A into PU polymer, the homogeneous structure of hybrid particle was preferred.
Polyurethane/polyaniline (PU/PANI) and polyurethane-poly(methyl methacrylate)/polyaniline (PU-PMMA/PANI) conductive core-shell particles were synthesized by a two-stage polymerization process. The first stage was to produce a core of PU or PU-PMMA via miniemulsion polymerization using sodium dodecyl sulfate (SDS) as the surfactant. The second stage was to synthesize the shell of polyaniline over the surface of core particles. Hydrogen chloride (HCl) and dodecyl benzenesulfonic acid (DBSA) were used as the dopant agents. APS was used as the oxidant for the polymerization of ANI. Different concentrations of HCl, DBSA and SDS would cause different conformations of PANI chains and thus different morphologies of PANI particles. UV-visible spectra revealed that the polaron band was blue-shifted due to the more coiled conformation of PANI chains by increasing the concentration of DBSA. Besides, with a high concentration of DBSA, both spherical- and rod-shape PANI particles were observed by transmission electron microscope (TEM) and the coverage of PANI particles onto the core surfaces was improved. The key point of formation of rod-type PANI particles was that DBSA was served with a high concentration accompanied with the existence of HCl or SDS. The better coverage of PANI particles over the core surfaces by charging higher DBSA concentrations resulted in a higher conductivity of hybrid particles.
Subjects
迷你乳化聚合
聚胺酯
聚苯胺
miniemulsion polymerization
PU
PANI
Type
thesis
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