Browsing by Author "Yei, DR"

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Enhanced thermal properties of PS nanocomposites formed from inorganic POSS-treated montmorillonite
(2004-04-13)
Yei, DR
;
Kuo, SW
;
Su, YC
;
Chang, FC
;
應用化學系
We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at up to a 3 wt% content of pristine clay relative to the amount of polystyrene (PS). We used two different surfactants for the montmorillonite: the aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS) and the ammonium salt of cetylpyridinium chloride (CPC). Both surfactants can intercalate into the layers of the pristine clay dispersed in water prior to polymerization. Although the d spacing of the POSS-intercalated clay is relatively smaller than that of the CPC-intercalated clay, PS more easily intercalates and exfoliates the POSS-treated clay than the CPC-treated clay. IR spectroscopic analysis further confirms the intercalation of POSS within the clay layers. We used X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The nanocomposite prepared from the clay treated with the POSS containing surfactant is exfoliated, while an intercalated clay was obtained from the CPC-treated surfactant. The molecular weights of polystyrene (PS) obtained from the nanocomposite is slightly lower than the virgin PS formed under similar polymerization conditions. The value of T, of the PS component in the nanocomposite is 8 degreesC higher than the virgin PS and its thermal decomposition temperature (21 degreesC) is also higher significantly. The presence of the POSS unit in the MMT enhances the thermal stability of the polystyrene. (C) 2004 Elsevier Ltd. All rights reserved.
Enhanced thermal properties of PS nanocomposites formed from montmorillonite treated with a surfactant/cyclodextrin inclusion complex
(2005-01-26)
Yei, DR
;
Kuo, SW
;
Fu, HK
;
Chang, FC
;
應用化學系
We have prepared polystyrene/clay nanocomposites using an emulsion polymerization technique. The nanocomposites were exfoliated at 3 wt% content of pristine clay relative to the amount of polystyrene (PS). We employed two surfactants for the montmorillonite: cetylpyridinium chloride (CPC) and the CPC/alpha-CD inclusion complex. Prior to polymerization, each surfactant intercalates into the layers of the pristine clay dispersed in water. The inclusion complex was characterized by X-ray diffraction, C-13 CP/MAS NMR spectra, and H-1 NMR spectroscopy, and TGA. X-ray powder patterns of the CPC/alpha-CD complex indicate that the alpha-CDs units form channels. The C-13 CP/MAS NMR spectrum of the complex suggests that a CPC chain is included in the channel formed by the alpha-CDs. The H-1 NMR spectra of the complexes indicate that the stoichiometry of the complexes is 1:2 (i.e. one CPC molecule and two alpha-CD units). The TGA reveals that the inclusion complex has higher thermal stability relative to the virgin CPC. We employed both X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structures of the nanocomposites. The value of T-g of the PS component in the nanocomposite is 6degreesC higher than that of the virgin PS and its thermal decomposition temperature is 33degreesC higher. The CPC/alpha-CD-treated clay is more effective than is virgin CPC-treated clay at enhancing the thermal stability of polystyrene. (C) 2004 Published by Elsevier Ltd.
Synthesis of a novel benzoxazine monomer-intercalated montmorillonite and the curing kinetics of polybenzoxazine/clay hybrid nanocomposites
(2006-01-15)
Yei, DR
;
Fu, HK
;
Chen, WY
;
Chang, FC
;
應用化學系
Polybenzoxazine (PBZ), which has a structure similar to that of phenolic resin, is formed through the thermal self-curing of benzoxazine, that is through a heterocyclic ring opening reaction that requires no catalyst and releases no condensation byproducts. We have used the solvent blending method to prepare PBZ/clay nanocomposites possessing various clay contents. We synthesized a monofunctional benzoxazine monomer (MBM) and then treated the clay with this intercalation agent. The results of X-ray diffraction (XRD) analysis indicated that MBM intercalated into the galleries of the clay; the nanocomposite possessed an exfoliated structure at 3% clay content. To better understand the curing kinetics of the PBZ/clay nanocomposites, we performed dynamic and isothermal differential scanning calorimetry (DSC) measurements. We describe the thermodynamics of the curing process, using all three of the Kissinger, Ozawa, and Kamal models. The Kissinger and Ozawa methods gave fairly close results for the calculated activation energies, which decreased upon increasing the clay content. The Kamal method, based on an autocatalytic model, suggested a total reaction order of between 2.4 and 2.8. The glass transition temperature (T,) decreased upon increasing the clay content. Thermogravimetric analysis (TGA) indicated that the nanocomposites have higher decomposition temperatures than does the pristine PBZ; this finding suggests an enhancement in their thermal stability. (c) 2005 Wiley Periodicals, Inc.
The kinetics of B-a and P-a type copolybenzoxazine via the ring opening process
(2005-02-05)
Su, YC
;
Yei, DR
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The structure of benzoxazines is similar to that of phenolic resin through thermal self-curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn-Wall-Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn-Wall-Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. (C) 2004 Wiley Periodicals, Inc.
Thermal properties and hydrogen bonding in polymer blend of polybenzoxazine/poly(N-vinyl-2-pyrrolidone)
(2003-04-01)
Su, YC
;
Kuo, SW
;
Yei, DR
;
Xu, HY
;
Chang, FC
The thermal properties and hydrogen bonding behavior of B-a type polybenzoxazine (PBZZ)/PVP blends were investigated by DSC and FIFIR. The DSC result shows a single T-g over the entire compositions and a large positive deviation based on Kwei equation was observed in the T-g versus composition diagram, implying that strong hydrogen bonding interaction exists between PBZZ and PVP segments. The strength of hydrogen bonding interaction is in the order of inter-association between the hydroxyl group of PBZZ and the carbonyl group of PVP (K-A = 594 L mol(-1)) > self-association between the hydroxyl group of pure PBZZ (K-B = 72.6 L mol(-1)) > inter-association between the hydroxyl and the Mannich-based bridge of pure PBZZ (K-C < 10 L mol(-1)). Good correlation between DSC and FIFIR analysis were observed. (C) 2003 Elsevier Science Ltd. All rights reserved.