Curing Mechanism and Properties of Fluorenyl Epoxy Resin
|School||Harbin Engineering University|
|Keywords||Bisphenol fluorene Microwave-assisted synthesis Flourenyl epoxy resins Curing mechanism Thermal properties|
9,9-bis(4-hydroxyphenyl)-fluorene (BHPF) was synthesized from phenol and fluorenone as raw materials in the presence of methylsulfonic acid as catalyst and 3-mercaptopropionic acid as promoter by microwave-assisted synthesis technology. Fluorenyl epoxy resin, diglycidyl ether of 9,9-bis(4-hydroxyphenyl)-fluorene (DGEBF), was synthesized from the reaction of BHPF and epichlorohydrin by the method reported previously using NaOH as catalyst and hexadecyl trimetyl ammonium bromide as phase transfer catalyst. DGEBF was modified by blending with bisphenol A epoxy resin (E-51). Their chemical structures were determined by FT-IR, 1H NMR and 13C NMR analyses. The curing mechanism, curing dynamics, mechanical properties, thermal stabilities, and moisture and thermal resistance of the blending resins system containing amine curing agent and anhydride curing agent including accelerating agent and chromium 2-ethylhexanoate and the cured polymers were evaluated by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analyzer (DMA) and Thermogravimetric Analyzer (TGA).The experimental results show that the yield of BHPF was 85.3% under the optimal process conditions of the molar ratio of phenol to fluorenone was 8 to 1, the mass percentage of methylsulphonic acid was 2% of the total reactants, reaction temperature was 55℃and reaction time was 30 min, and the melting point of BHPF was 222-224℃. The reaction time and dosage of catalyst are reduced dramaticlly by microwave-assisted synthesis technology. The epoxy value of DGEBF was 0.41eq/100g, and the melting point was 150.5℃.The curing kinetics and curing craft of E-51/DGEBF was investigated using non-isothermal differential scanning calorimetry (DSC), and determined by Kissinger, Ozawa, Starink and Crane methods. Accelerant and catalyst of BDMA-Cr could lower the activation energy and reduce curing temperature with the curing agent being anhydride.The gel time of various anhydride was different, we found that MNA>HK-021>MeTHPA. Of amine curing agents, DDM was more active than DDS,as a result, the gel time of DDS was longer than DDM.Starink is more accurate than other methods, the activation energy of curing agents had the following rule:MeTHPA>DDS>DDM.Among the anhydrides, MeTHPA had better comprehensive performance than MNA and HK-021. Tg and T5% of cured resins declined when the content of E-51 increased. The optimum adding amount of E-51 was 50%, and the best proportion of anhydrides to epoxy resins was 1:1. BDMA had the best promoting effect, and the optimal addition amounts of BDMA and Cr were 2% and 1% respectively. However, with the addition of BDMA-Cr, the mechanical property and thermal property of cured resins was degraded. Tg and T5% of cured resins had the rule as follows:DDS>DDM>MeTHPA.The water abosptioin of cured resins reduced with the content of DGEBF in the epoxy blends increasing, since phenyl rings in fluorene group increased and abated the polarity. MeTHPA had the best moisture-proof, the moisture abosptioin of cured resins with different curing agents had the rule as MeTHPA<DDM<DDS.Cr could lower water-intake rate of cured resins, and effectively kept the performance of them.