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Mechanism of transesterification and cyclization of epoxy-polycarbonate blends catalyzed by quarternary ammonium salt
(1996-11-30)
Li, MS
;
Ma, CCM
;
Lu, MS
;
Lin, ML
;
Chang, FC
The reaction of oxirane with carbonate using quarternary ammonium salts as catalyst has been studied. Curing is caused by the transesterification reaction of the oxirane cycle with the carbonate group that proceeds by an ''insertion'' mechanism in the stoichiometric system. The ratio of the reactants is two oxirane groups to one carbonate group. In the nonstoichiometric system, the epoxide content is more than the stoichiometric quantity required. A cyclization reaction is followed by the transesterification reaction. To identify the finished products, a model reaction was proposed using diphenyl carbonate and phenyl glycidyl ether which results in the formation of 4-phenoxymethyl-1,3-dioxolane-2-one (PMD). The mechanism of forming the cyclic structure is assumed to proceed through the chain scission of the network in which the molecular chain crosslinked with carbonate group by a transesterification reaction. (C) 1996 John Wiley & Sons,Inc.
Miscibility in blends of liquid crystalline poly(p-oxybenzoate-co-p-phenyleneisophthalate) and polycarbonate
(1997-07-01)
Wei, KH
;
Jang, HC
;
Ho, JC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The miscibility of liquid crystalline poly(p-oxybenzoate-co-p-phenyleneisophthalate) (HIQ) and polycarbonate (PC) was investigated with differential scanning calorimetry (d.s.c.). It was found that blends of liquid crystalline HIQ and PC showed a single glass transition temperature across the whole composition range. Annealing these blends at temperatures slightly above the melting point of HIQ, ester exchange occurred as confirmed both by i.r. and n.m.r. spectroscopy. The apparent miscibility of HIQ and PC was caused by this reaction. The blends retained liquid crystalline characteristics in the first few reaction minutes. As the transesterification continued, the bisphenol-A segment in PC reacted with both isophthalate and oxybenzoate segments in HIQ. This resulted in amorphous polymers. These amorphous polymers exhibited a single glass transition temperature higher than that for both pure polymers. (C) 1997 Elsevier Science Ltd.
The epoxy-polycarbonate blends cured with aliphatic amine .2. Thermal and mechanical properties mechanisms
(1997-09-30)
Lin, ML
;
Chang, KH
;
Chang, FC
;
Li, MS
;
Ma, CCM
The transamidation reaction converts the carbonate and amine into N-aliphatic aromatic carbamate and urea, causing the equivalent of oxirane and amine nonstoichiometric in the primary cure stage. After postcure, the substitution reaction takes place and results in a more tightly crosslinked structure. Such a higher crosslinking density is responsible for higher T-g, tensile strength, and tensile modulus in the postcure stage than that in the primary and secondary cure stages. This trend is more pronounced in those PC-epoxy blends containing higher molecular weight aliphatic amine or a higher content of PC. This phenomenon is due to the difference in the fraction of amino group of aliphatic amine consumed in the transamidation. PC-epoxy/aliphatic amine blends show minor improvement in the high strain rate Izod impact tests, while toughness improvement for some blends is substantial at low strain rate tensile tests. (C) 1997 John Wiley & Sons, Inc.
The epoxy-polycarbonate blends cured with aliphatic amine .1. Mechanism and kinetics
(1997-09-30)
Lin, ML
;
Chang, KH
;
Chang, FC
;
Li, MS
;
Ma, CCM
Reaction mechanism of the PC-epoxy blends cured by aliphatic amine has been investigated by varying PC contents in the blends. The transamidation reaction tends to convert nearly all the carbonates into N-aliphatic aromatic carbamates even at ambient temperature before normal curing. The remaining amine proceeds the normal curing with epoxy at a higher temperature (80 degrees C). For the PC-epoxy/aliphatic amine blend containing 6 wt % PC, the yielded N-aliphatic aromatic carbamate further reacts with amine to produce the urea structure. The urea undergoes substitution reaction with the hydroxyl formed from the normal curing to give the N-aliphatic aliphatic carbamate. For the blend containing 12 wt % PC, the N-aliphatic aromatic carbamate converts into the N-aliphatic aliphatic carbamate via two different routes. For the blend containing lower molecular weight of the aliphatic amine, the N-aliphatic aromatic carbamate reacts with hydroxyl to form the N-aliphatic aliphatic carbamate directly. For the blend containing higher molecular weight of aliphatic amine, the N-aliphatic aromatic carbamate decomposes into the aliphatic isocyanate accelerated by the presence of the residual oxirane. The isocyanate formed then reacts with hydroxyl to yield the N-aliphatic aliphatic carbamate. The activation energy (E-alpha) and preexponential factor (A) of the PC-epoxy/POPDA blends decrease with the increase of the PC content. Kinetic study by thermal analysis by the method of autocatalyzed model is able to correctly predict oxirane conversion vs. time relationship for the neat epoxy/aliphatic amine and the PC-epoxy/aromatic amine systems because the dominant reaction is the normal curing reaction between amine and oxirane. The model fails to predict the PC-epoxy/aliphatic amine system because the system is complicated by several other reactions besides the normal curing reaction. (C) 1997 John Wiley & Sons, Inc.
The kinetics, thermal and mechanical properties of epoxy-polycarbonate blends cured with aromatic amine
(1998-04-01)
Lu, MS
;
Chen, JL
;
Li, YS
;
Chang, FC
;
Li, MS
PC-DER331 blends are transparent and homogeneous due to the transesterification taking place during hot melting process. This transesterification reaction does not occur or occurs insignificantly during the preparation of PC-DER332 blends. PC is separated from the PC-DER332 melt mixture by slow cooling to room temperature but the mixture remains a single phase by quenching with an ice bath. Two systems of PC-epoxy blends, PC-DER331 blends and PCDER332 blends are cured by the m-phenylene diamine (MPDA) in a stoichiometric ratio. Curing kinetics have been carried out by differential scanning calorimeter (DSC). The presence of PC accelerates the curing reaction. Infrared spectroscopy (IR) indicates the occurrence of transesterification in the PC-DER331/MPDA blends during curing. The flexural modulus increases with the increase of the PC content while the notched Izod impact strength decreases with the increase of the PC content for all the blending systems. The fracture surfaces of the PC-DER331/MPDA blends are smooth, an indication of a homogeneous morphology. The fracture surfaces of the PC-DER332/MPDA blends are rough, an indication of a heterogeneous morphology.
Miscibility and transesterification in blends of liquid crystalline copolyesters and polyarylate
(1998-08-01)
Tyan, HL
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Blends of poly(oxybenzoate-p-ethylene terephthalate) (POB-PET) and polyarylate were confirmed to be a partially miscible system by differential scanning calorimetry. When 60/40 POB-PET/PAr blend was annealed at high temperature (above 270 degrees C) for several minutes, the ester-ester interchange( transesterification)in the blend took place immediately, as evidenced by Fourier Transformed infrared analyses. The analysis of the blend annealed at 290 degrees C by H-1-C-13 nuclear magnetic resonance disclosed that there were four new diads appearing in 15 min and an additional one produced in 60 min during the heat treatment. The miscibility between POB-PET and polyarylate increased with the mol concentration of these new diads judging from differential scanning calorimetry. The evolution of the concentration of the diad ethylene glycol-isophthalate during the annealing can be described by a second-order reaction. The activation energy of forming the diad ethylene glycol-isophthalate was 26.5 kcal/mol, and the preexponential factor for the transesterification reaction is 3.7 x 10(8) min(-1). (C) 1998 John Wiley & Sons, Inc.
Transesterification in homogeneous poly(epsilon-caprolactone)-epoxy blends
(1999-01-03)
Chen, JL
;
Huang, HM
;
Li, MS
;
Chang, FC
;
應用化學系
Transesterification has been investigated in poly(epsilon-caprolactone) (PCL)-epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol-il (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring-opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA-3,3'-dimethylmethylene-di(cyclohexylamine)-PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T-g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. (C) 1999 John Wiley & Sons, Inc.
The kinetics of transesterification in blends of liquid crystalline copolyester and polycarbonate
(1999-02-01)
Ho, JC
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The kinetics of transesterification in blends of thermotropic copoly(oxybenzoate-ethylene terephthalate) and polycarbonate at melt state were analysed quantitatively with C-13 nuclear magnetic resonance, and were then modelled by a phenomenological equation. It was found that the activation energy for the transesterification reaction between the poly(oxybenzoate) segment in copoly(oxybenzoate-ethylene terephthalate) and polycarbonate was more than twice that for the transesterification reaction between the poly(ethylene terephthalate) segment and polycarbonate (i.e. 94.6 versus 41.8 kcal/mol). This is probably due to the stronger chemical bond in oxybenzoate-oxybenzoate that in ethylene-terephthalate. Additionally, owing to the rigid-rod nature of the poly(oxybenzoate) segment, the frequency factor in the transesterification reaction in poly(oxybenzoate) segment and polycarbonate is much higher than that in poly(ethylene terephthalate) segment and polycarbonate (i.e. 10(36) versus 10(14) min(-1)). (C) 1998 Elsevier Science Ltd. All rights reserved.
The mechanical properties of ternary liquid-crystalline polymer blends
(1996-05-01)
Wei, KH
;
Hwang, WJ
;
Tyan, HL
;
交大名義發表
;
材料科學與工程學系
The possibility of improving the compatibility of and the adhesion between liquid-crystalline poly(oxybenzoate-co-oxynaphthoate) (Vectra) and polycarbonate (PC) by adding a stable compatibilizer based upon the transesterification between liquid-crystalline poly(oxybenzoate-co-ethylene terephthalate) (POB/PET) (60/40) and polycarbonate was investigated. The goal was to provide a physical interaction between the matrix polymer and the liquid-crystalline polymer through a third polymer that contained similar chemical structural units to those in both polymers. It was found that at proper compositions the adhesion between Vectra and PC was greatly improved by the presence of the compatibilizer, as indicated by the morphological evidence. These ternary liquid-crystalline polymer blends displayed improved ultimate tensile stress (30% increase as compared to PC) and elongation at break (seven times as compared to binary blend) even under a nominal injection-moulding process. The impact property of the ternary liquid-crystalline polymer blend was also improved as compared to that of the binary liquid-crystalline polymer blends. Copyright (C) 1996 Elsevier Science Ltd.
Mechanism of transesterification and cyclization of epoxy-polycarbonate blends catalyzed by quarternary ammonium salt
(1996-11-30)
Li, MS
;
Ma, CCM
;
Lu, MS
;
Lin, ML
;
Chang, FC
The reaction of oxirane with carbonate using quarternary ammonium salts as catalyst has been studied. Curing is caused by the transesterification reaction of the oxirane cycle with the carbonate group that proceeds by an ''insertion'' mechanism in the stoichiometric system. The ratio of the reactants is two oxirane groups to one carbonate group. In the nonstoichiometric system, the epoxide content is more than the stoichiometric quantity required. A cyclization reaction is followed by the transesterification reaction. To identify the finished products, a model reaction was proposed using diphenyl carbonate and phenyl glycidyl ether which results in the formation of 4-phenoxymethyl-1,3-dioxolane-2-one (PMD). The mechanism of forming the cyclic structure is assumed to proceed through the chain scission of the network in which the molecular chain crosslinked with carbonate group by a transesterification reaction. (C) 1996 John Wiley & Sons,Inc.

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