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Author: search.filters.author.Chen, JLSubject: search.filters.subject.epoxy

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Now showing 1 - 6 of 6
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    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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    Item type:Item,
    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.
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    Item type:Item,
    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.
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    Temperature-dependent phase behavior in poly(epsilon-caprolactone)-epoxy blends
    (2001-03-01)
    Chen, JL
    ;
    Chang, FC
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The cured morphologies of poly(epsilon -caprolactone)/epoxy (PCL/epoxy) blends are examined by SEM micrographs. The phase separation mechanism of the blend can be deduced from cured morphologies influenced by the blend compositions and curing conditions. The LCST phase diagram is proposed for the system and the location of the critical point shifts with the curing temperature, which results in the change of phase separation mechanism. The curing rate promoted by higher curing temperature also influences the morphologies of the blends. The fraction of the epoxy-rich macrophase resulted from the long-distance diffusion decreases with the increase of the curing temperature. In contrast, the domain size of the epoxy microphase increases with the curing temperature, which cannot be dominated by the epoxy curing rate. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Item type:Item,
    Phase separation and melting behavior in poly(epsilon-caprolactone)-epoxy blends cured by 3,3'-dimethylmethylene-di(cyclohexylamine)
    (2003-09-12)
    Chen, JL
    ;
    Chang, FC
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The morphology and the melting behavior of poly(E-caprolactone)/epoxy blends (PCL/epoxy) have been investigated by SEM and DSC. The mechanism of phase separation varies with the curing temperature and PCL content, which can be deduced from the cured morphology of the blend. Higher temperature leads to lower blend viscosity and a higher curing rate, and the final morphology is determined by the competition of these two factors. The PCL melting behavior of the blend is influenced by the extent of phase separation and crystallization during curing. The dual melting behavior of the PCL blend can be ascribed to the interference of the epoxy, which results in the formation of less perfect PCL crystallites melted at lower temperature. (C) 2003 Wiley Periodicals, Inc.
  • Thumbnail Image
    Item type:Item,
    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.