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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.
Reactive compatibilization of polymer blends of poly(butylene terephthalate) (PBT) and polyamide-6,6 (PA66) .1. Rheological and thermal properties
(1997-04-01)
Huang, CC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Epoxy resin (EEW = 2060) has been demonstrated to be an efficient reactive compatibilizer for the incompatible polymer blends of polyamide-6,6 (PA66) and poly(butylene terephthalate) (PET). Processability improvement has been achieved by reducing die swell and melt fracture during blending extrusion. Reactions involved in this three-component system are very complex but only the coupling reactions between epoxy and PBT and PA66 endgroups are considered essential. This epoxy resin is more compatible with PET than with PA66 but the reactivity of the former is slower than that of the latter. Additionally, PET has a lower melting temperature than that of PA66; this epoxy resin therefore has the first chance to react with PBT, then with PA66, at the interface. Certain mixed copolymers, epoxy-co-PBT-co-PA66, are expected to be formed and to anchor at the interface. These mixed copolymers are believed to be the major contributor in improving the compatibility of incompatible PA66/PBT blends. (C) 1997 Elsevier Science Ltd.
Precrack hysteresis energy in determining polycarbonate ductile-brittle transition .4. Effect of strain rate
(1997-07-25)
Chiou, KC
;
Hsu, HC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Effect of deformation rate on the ductile-brittle transition behavior for polycarbonate (PC) with different molar mass, notch radius, and rubber content has been investigated. PC with higher molar mass, notch radius, or rubber-modification possesses a higher critical strain rate when the ductile-brittle transition occurs. Whether a notched specimen will fail in a ductile mode or a brittle mode is already decided before the onset of the crack initiation. If size of the precrack plastic zone exceeds a critical level prior to onset of crack initiation, the crack extension developed later will propagate within the plastic zone and result in a ductile mode fracture. The precrack elastic storage energy, the input energy subtracting the hysteresis energy, is the main driving force to strain the crack tip for crack initiation. The precrack hysteresis energy (directly related to the precrack plasticity) increases with the decrease of the applied strain rate. Therefore, the strain rate is also closely related to the size of the precrack plastic zone. If the strain rate is lower than the critical strain rate, the specimen is able to grow a precrack plastic zone exceeding the critical plastic zone and results in a ductile mode fracture. (C) 1997 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.
Preparation and epoxy curing of novel dicyclopentadiene-derived Mannich amines
(1997-09-07)
Lin, JJ
;
Lin, SF
;
Chang, FC
;
Tseng, FP
;
應用化學系
Reactive compatibilization of the poly(ethylene terephthalate) liquid crystalline polymer blends by solid epoxy resin as a coupling agent
(1996-06-27)
Chin, HC
;
Chiou, KC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A selected reactive coupling agent can be served as an effective compatibilizer for certain immiscible and incompatible blends should both blend constituents possess the necessary functional groups that can react with the coupling agent at comparable rates. Solid epoxy resin with two epoxide endgroups per molecule was demonstrated to be an efficient reactive compatibilizer for the incompatible blends of poly(ethylene terephthalate) (PET) and co-polyester liquid crystalline polymer (LCP) by functioning as a coupling agent. The main chain structure of the epoxy resin is neither identical nor miscible with PET and LCP and tends to reside at interface during melt mixing. This preferential residence gives the epoxy compatibilizer greater opportunity to react with both PET and LCP simultaneously to produce the in situ-formed epoxy-b-PET-b-LCP mixed copolymer. This in situ-formed mixed copolymer is highly effective in compatibilizing the PET/LCP blends. This reactive epoxy compatibilizer enhances the LCP fibril formation and results in substantial improvements on stiffness and toughness of the PET/LCP blends. (C) 1996 John Wiley & Sons, Inc.
Sequential distribution of main chain phosphorous-containing copolyesters characterized by H-1 NMR
(1998-01-01)
Chang, SJ
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A series of main chain phosphorus-containing copolyesters were synthesized by polycondensation of terephthalic acid (TPA), ethylene glycol (EG) and phenyl phosphonic acid (PPA). Chemical structures of these main chain phosphorus-containing copolyesters were characterized by H-1 NMR. Experimental results show that the resonance intensity of PPA aromatic protons increases with increase of the phosphorus content. The chemical shifts of the ethylene protons in the ethylene glycol units vary with different sequences. The resonance chemical shift of the ethylene protons of the T-E-T unit is higher than those of P-E-T (T-E-P) and P-E-P units. The monomer molar fraction, sequential distribution and degree of randomness of the phosphorus-containing copolyesters were determined through analyses of the ethylene protons in the ethylene glycol units. The molar fractions of the PPA comonomer determined by H-1 NMR analyses are close to the values determined by a UV method. The degree of randomness for the copolyesters was found to be in the range 0.66-0.83. (C) 1998 SCI.
Polymer blends of PBT and PP compatibilized by ethylene-co-glycidyl methacrylate copolymers
(1996-07-11)
Tsai, CH
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The ethylene-co-glycidyl methacrylate (EC) copolymer is an efficient reactive compatibilizer for polymer blends of poly(butylene terephthalate) (PET) and polypropylene (PP). During melt processing, the epoxy functional group of the EG copolymer can react with the PET carboxylic acid and/or hydroxyl terminal groups at the interface to form various EG-g-PBT copolymers. These in situ formed grafted copolymers tend to concentrate along the interface to reduce the interfacial tension at the melt and result in finer phase domains. Higher glycidyl methacrylate (GMA) content in the EG copolymer or a higher quantity of the EG compatibilizer in the blend results in a better compatibilized blend in terms of finer phase domains, higher viscosity, and better mechanical properties. The presence of only 50 ppm catalyst (ethyltriphenyl phosphonium bromide)in the EG compatibilized blend further improves the blend compatibility substantially. (C) 1996 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.

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