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Crystallization kinetics and crystallization behavior of syndiotactic polystyrene/clay nanocomposites
(2001-09-01)
Tseng, CR
;
Lee, HY
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
We investigated the effects of montmorillonite (clay) on the crystallization kinetics of syndiotactic polystyrene (sPS) with isothermal differential scanning calorimetry analyses. The clay was dispersed into the sPS matrix via melt blending on a scale of 1-2 nm or up to about 100 nih, depending on the surfactant treatment. For a crystallization temperature of 240 degreesC, the isothermal crystallization data were fitted well with the Avrami crystallization equation. Crystallization data on the kinetic parameters (i.e., the crystallization rate constant, Avrami exponent, clay content, and clay/surfactant cation-exchange ratio), were also investigated. Experimental results indicated that the crystallization rate constant of the sPS nanocomposite increased with increasing clay content. The clay played a vital role in facilitating the formation on the thermodynamically more favorable all-beta -form crystal when the sPS was melt-crystallized. (C) 2001 John Wiley & Sons, Inc.
Preparation and crystallization behavior of syndiotactic polystyrene-clay nanocomposites
(2001-12-01)
Tseng, CR
;
Wu, JY
;
Lee, HY
;
Chang, FC
;
應用化學系
Syndiotactic polystyrene/modified-clay nanocomposites have been prepared by solution blending by mixing pure s-PS and organophilic clay with adsorbed cetyl pyridium chloride (CPC) in dichlorobenzene. The dispersability of the clay in syndiotactic polystyrene/modified-clay nanocomposites was studied using X-ray and transmission electron microscopy. The clay is well dispersed into the s-PS matrix using solution blending with scale in 1-2 nm or in a few tenths similar to 100 nm depending on surfactant treatment. The CPC is partially compatible with s-PS and allows syndiotactic polystyrene chains intercalating into clay layers. The crystallization behavior of alpha- and beta -crystals for syndiotactic polystyrene nanocomposite has been thoroughly examined using the Fourier transform infrared and differential scanning calorimetry. Our results further demonstrate that the presence of the clay plays a vital role in facilitating the formation on the thermodynamically more favorable beta form crystal when the s-PS is melt- or cold-crystallized. (C) 2001 Elsevier Science Ltd. All rights reserved.
Poly(acetoxystyrene-co-isobutylstyryl POSS) nanocomposites: Characterization and molecular interaction
(2002)
Xu, HY
;
Kuo, SW
;
Huang, CF
;
Chang, FC
;
應用化學系
The poly (acetoxy styrene-co-isobutyl styryl polyhedral oligomeric silsesquioxanes)s (PAS-POSS) were synthesized by free radical polymerization and characterized by FTIR, high resolution NMR, FTIR, GPC, and DSC. The results show that the POSS content can be controlled by varying the POSS feed ratios. The interactions between organic components and inorganic POSS core, and the effects of inorganic POSS core on the properties of the resulting hybrids were investigated by high resolution solid state C-13 NMR, Si-29 NMR and FTIR spectra. The results provide detailed understandings of the effects of POSS moiety on properties of hybrid polymers.
Glass transition temperatures of poly(hydroxystyrene-co-vinylpyrrolidone-co-isobutylstyry1 polyhedral oligosilsesquioxanes)
(2002-09-01)
Xu, HY
;
Kuo, SW
;
Lee, JS
;
Chang, FC
;
應用化學系
A series of poly(hydroxystyrene-co-vinylpyffolidone-co-isobutylstyryl polyhedral oligosilsesquioxanes) (PHS-PVP-POSS) hybrid polymers with various POSS contents was prepared by free radical copolymerization of acetoxystyrene, vinylpyrrolidone with styrylisobutylpolyhedral oligosilsesquioxanes (POSS), followed by selective removal of the acetyl protective group. The POSS content of a hybrid polymer can be effectively controlled by varying the feed ratios of reactants. The T-g of the POSS hybrid increases with the POSS content of PHS-PVP-POSS hybrids. The mechanism of T-g enhancement in these PHS-PVP-POSS hybrids was investigated using DSC, FTIR and GPC. The formation of the physically cross-linked POSS in these hybrid polymers trends to restrict polymer chain motion and results in significant T-g increase. (C) 2002 Published by Elsevier Science Ltd.
Crystallization behavior of syndiotactic polystyrene nanocomposites for melt- and cold-crystallizations
(2002-12-05)
Tseng, CR
;
Wu, SC
;
Wu, JJ
;
Chang, FC
;
應用化學系
Analyses of the effects of montmorillonite (clay) on the crystallinity and crystallization behavior of syndiotactic polystyrene (s-PS) were investigated by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The dispersibility of the clay in s-PS nanocomposites was studied by X-ray and transmission electron microscopy (TEM). The clay was dispersed into the s-PS matrix by melt blending on a scale of 1-2 nm or few tenths-100 nm, depending on the surfactant treatment. On adding clay, the crystallization behavior of the s-PS tends to convert into the beta-crystal from the alpha-crystal after being cold-crystallized because the clay plays a vital role in facilitating the formation of the thermodynamically favored beta-form crystal when the s-PS is cold- or melt-crystallized. This phenomenon leads to a change in a conventional mechanism of molecular packing for the s-PS. Evidently, the clay significantly affects the crystallinity and crystallization behavior of the s-PS. (C) 2002 Wiley Periodicals, Inc.
Syntheses and characterizations of in situ blended metallocence polyethylene/clay nanocomposites
(2003-12-01)
Kuo, SW
;
Huang, WJ
;
Huang, SB
;
Kao, HC
;
Chang, FC
In this paper, we report the preparation of in situ blends of metallocence polyethylene (mPE) with montmorillonite (clay). The polymerization activity of polyethylene decreases upon increasing the amount of the clay feed. The mPE nanocomposites still possess their original melting and crystallization temperatures, but the melting and crystallization enthalpies decrease upon increasing the clay content. In addition, the polymer interaction parameter between mPE and exfoliated clay sheets was calculated to be -0.204 based on a modified Kim-Bae equilibrium melting depression equation. All of the isothermal crystallization kinetics data fit well to the Avrami crystallization equation. We found that increasing the clay content results in a faster rate of crystallization, but pure mPE still crystallizes the fastest. Using a small amount of pretreated clay results in a more homogeneous and finer dispersion of the clay in the polymer matrix, as determined by wide-angle X-ray diffraction and transmission electron microscopy analyses. Both the values of T-1rho(H) in the solid-state NMR spectra of the fast and slow components show increment upon increasing the clay content, which indicates that either the mobile phase tends to increase its rigidity in the clay-containing system. (C) 2003 Elsevier Ltd. All rights reserved.
Characterization of poly(vinyl pyrrolidone-co-isobutylstyryl polyhedral oligomeric silsesquioxane) nanocomposites
(2004-02-15)
Xu, HY
;
Kuo, SW
;
Huang, CF
;
Chang, FC
;
應用化學系
Poly(vinyl pyrrolidone-co-isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP-POSS) were synthesized by one-step polymerization and characterized 13 using FTIR, high-resolution H-1-NMR, solid-state C-13-NMR, Si-29-NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The T-g of the PVP-FOSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self-association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low FOSS content, the role as diluent dominates, resulting in a decrease in T-g. At a relatively high POSS content, the last two factors dominate and result in T-g increase of the PVP-POSS hybrid. (C) 2003 Wiley Periodicals, Inc.
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.
Syntheses, thermal properties, and phase morphologies of novel benzoxazines functionalized with polyhedral oligomeric silsesquioxane (POSS) nanocomposites
(2004-08-19)
Lee, YJ
;
Kuo, SW
;
Su, YC
;
Chen, JK
;
Tu, CW
We have successfully synthesized a novel benzoxazine ring-containing polyhedral oligomeric silsesquioxane (BZ-POSS) monomer by two routes: (1) hydrosilylation of a vinyl-terminated benzoxazine using the hydro-silane functional group of a polyhedral oligomeric silsesquioxane (H-POSS) and (2) reaction of a primary amine-containng POSS (Amine-POSS) with phenol and formaldehyde. The benzoxazine-containing POSS (BZ-POSS) monomer can be copolymerized with other benzoxazine monomers through ring-opening polymerization under conditions similar to that used for polymerizing pure benzoxazines. Thermal properties of these POSS-containing organic/inorganic polybenzoxazine nanocomposites have been improved over the pure polybenzoxazine analyzed by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The BZ-POSS monomer is poorly miscible with the benzoxazine monomer and tends to aggregate and forms its own domains, both before and after polymerization. At a higher BZ-POSS content, gross aggregation occurs and results in a lower than expected improvement in the thermal properties. (C) 2004 Elsevier Ltd. All rights reserved.
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.

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