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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.
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.
Transesterification and cyclization of polycarbonate-epoxy blends cured with anhydride
(1996-08-01)
Li, MS
;
Su, YF
;
Ma, CCM
;
Chen, JL
;
Lu, MS
Infrared spectra have been investigated to study the curing mechanisms of polycarbonate-epoxy blends using anhydride as a hardener catalysed by tertiary amine. Due to a significant difference in the reaction, curing reactions of the system can be considered as two sequential stages: (1) an anionic alternating copolymerization of cyclic anhydride and epoxy resin, and (2) a homopolymerization of oxirane initiated by a quaternary ammonium salt zwitter ion. The transesterification/cyclization of carbonate groups proceeds in the later stage if the oxirane is still available. Degrees of transesterification/cyclization and homopolymerization are higher when a higher epoxy/anhydride ratio is used. This study positively confirms the mechanism of transesterification/cyclization proceeding through a zwitter ion. The zwitter ion is formed from epoxide and tertiary amine, which attacks the carbonate group. Copyright (C) 1996 Elsevier Science Ltd.
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.
Polymer blends of polyamide-6 (PA6) and poly(phenylene ether) (PPE) compatibilized by a multifunctional epoxy coupler
(1998-08-01)
Chiang, CR
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A tetrafunctional epoxy monomer, N,N,N'-N' -tetraglycidyl-4,4'-diaminodiphenyl methane (TGDDM),has demonstrated to be a highly efficient reactive compatibilizer in compatibilizing the immiscible and incompatible polymer blends of polyamide-6 (PA6) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE). This epoxy coupler can react with both PA6 and PPE to form various PA6-co-TGDDM-co-PPE mixed copolymers. These interfacially formed PAG-co-TGDDM-co-PPE copolymers tend to anchor along the interface to reduce the interfacial tension and result in finer phase domains and enhanced interfacial adhesion. A simple one-step melt blending has demonstrated to be more efficient in producing a better compatibilized PA6/PPE blend than a two-step sequential blending. The mechanical property improvement of the compatibilized blend over the uncompatibilized counterpart is very drastic, by considering the addition of a very small amount, a few fractions of 1%, of this epoxy coupling agent. (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.
Synthesis, characterization, thermal and flame-retardant properties of silicon-based epoxy resins
(1999-08-15)
Hsiue, GH
;
Wang, WJ
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A new silicon-containing oxirane triglycidyl phenyl silane oxide (TGPSO) and its corresponding silicon-containing epoxy resins are synthesized and characterized. The activation energies of TGPSO curing reaction with various curing agents, including 4,4-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, and dicyanodiaminde, are found to be 180, 196.5, and 154 kJ/mol. The curing reaction of TGPSO with diamines is determined to be a first-order reaction through means of Arrhenius plots. The introduction of the silicon-containing group results in higher curing reactivity. This silicon-containing resin possesses higher char yield as well as higher limiting oxygen index (LOI = 35) than the commercial epoxy resins, confirming the usefulness of these silicon-containing epoxy resins as flame retardants. Char yields and LOI measurements demonstrate that incorporating silicon into epoxy resins is able to improve their flame retardancy. (C) 1999 John Wiley & Sons, Inc.
Kinetics and curing mechanism of epoxy and boron trifluoride monoethyl amine complex system
(1999-09-15)
Li, YS
;
Li, MS
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The kinetics of cationic polymerization of epoxy resin has been studied. Due to multiple reaction exotherms and irregular baselines involved in this system, the ASTM E 698 method was chosen to determine the kinetic parameters of this epoxy/BF3-MEA system. The DER 332/BF3-MEA system follows the first order active chain end (ACE) reaction mechanism. The adding of the hydroxyl group into the system is prone to decrease the activation energy and shifts the curing into the activated monomer (AM) mechanism due to the stronger nucleophilicity of the hydroxyl group than the epoxide group. On the other hand, the DER 331/BF3-MEA system possesses lower activation energy because the DER 331 contains more hydroxyl groups-alpha-glycol and secondary alcohol. The former is the major contributor in lowering the activation energy. The hydroxyl group also can act as a chain transfer agent by retarding the propagation process, thus the reaction rate of the DER 332/BF3-MEA system is higher than the DER 331/BF3-MEA system. The DER 332/BF3-MEA system shows good correlation between the experimental data (FT-IR, DSC, and GPC) and the simulation curve based on ASTM E 698 before gelation, while a larger deviation is observed in the DER 331/BF3-MEA system. After gelation, the hydroxyl group also acts as an active site to react with residual epoxy monomers and obtain a more condense matrix. (C) 1999 John Wiley & Sons, Inc.
In-situ measurement of the crystallization process of polycarbonate/epoxy resin by a photoresistor
(2000-03-01)
Li, YS
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The PC crystallization process is measured by the photoresistor, by which the reciprocal relationship is obtained between the illumination of transmission light and the resistance. In the beginning of annealing the change of resistance is insignificant when the crystallization is still at the induction stage. Then the increasing number and size of spherulites scatter the incoming light and the resistance increases quickly. Finally the concentration of amorphous PC decreases and the increasing rate of resistance slows down. The X-ray pattern shows an ordered PC structure of 2 theta = 11 degrees in the induction period, then converts to amorphous (broad peak at 20 degrees) and spherulite (17.2 degrees) structure. The dissolving heat of PC spherulite, analyzed by differential scanning calorimetry, shows a linear relationship to the resistance. Thus the relative crystallinity can be obtained by measuring the resistance of the photoresistor from both primary and secondary crystallization. The experimental results show good correlation to the Avrami model and the highest crystallization rate is obtained at 80 degrees C. The thermodynamic factor controls the crystallization rate at higher annealing temperature while the kinetic factor dominates the crystallization rate at lower annealing temperatures. (C) 1999 Elsevier Science Ltd. All rights reserved.

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