| Epoxy resins have been widely used in the field of mechanical, electronic, aerospace industry, and advanced composites due to their good adhesion, dimensional stability, low shrinkage, good chemical resistance, high mechanical strength, and good processability. However, further application of traditional epoxy resins is limited by its brittleness and relatively high dielectric constant.Hyperbranched epoxy (HPE) combines the characteristics of hyperbranched polymers and epoxy resins. HPE is highly branched, lack of chain entanglement, and has three dimensional globular structure and good solubility. Its viscosity is lower than that of conventional linear polymers with the same molecular weight. In addition, HPE has a lot of inter-and intra-molecule free volume which can by maintained after cured. Therefore, HPE can be potentially used to prepare high performance materials.This work designed and synthesized a novel fluorine containing epoxy (FDE). FDE was added in to diglycidyl ether of bisphenol A (DGEBA) as a modifier and effects on thermal and dielectric properties were investigated.A flexible hyperbranched polyether epoxy (HBPEE) and a rigid epoxidized hyperbranched poly(phenylene oxide)(EHPPO) were designed and synthesized. Both of the hyperbranched epoxies were used as a toughener for DGEBA. Effects of molecular backbone, molecular weight, and free volume on toughening were investigated and toughening mechanism was discussed. In addition, an non-reactive end-capped hyperbranched poly(phenylene oxide)(CHPPO) was prepared and used as a non-reactive modifier for DGEBA.The main content includes:1. A novel fluorine-containing epoxy4-fluoro-4’,4"-diepoxypropoxy triphenyl methane (FDE) was designed and synthesized from two commercially available materials. The structure of FDE is well characterized. As a modifier, FDE was added in to DGEBA and cured by methyl nadic anhydride. By comparing with cured neat FDE and DGEBA, effects of FDE on thermal properties, dielectric properties, and water absorption were investigated. Results show that both glass transition temperature (Tg) and5%weight loss degradation temperature (Td5%) of cured FDE are nearly60℃higher than that of DGEBA. And cured FDE has much lower dielectric constant and water absorption. Furthermore, addition of FDE into DGEBA can improve the thermal and dielectric properties of the hybrids.2. A novel liquid hyperbranched polyether epoxy (HBPEE) based on hydroquinone and1,1,1-trihydroxymethylpropane triglycidyl ether was synthesized through an A2+B3proton transfer polymerization. Polymerization in tetrahydrofuran and in bulk was investigated, respectively. Effects of different reaction conditions on polymerization were discussed. Rheology behavior of HBPEE was characterized and master curve was obtained. As a toughener for DGEBA, the addition of HBPEE can improve the impact strength of the cured hybrids remarkably without sacrificing the tensile strength. Improvement of tougheness can be attributed to the flexible chains and large amount of free volume incorporated by hyperbranched structure. The toughening mechanism could be explained by in situ toughening mechanism. Although addition of HBPEE leads to a decrease in Tg of cured hybrids, it has minimal effects on the thermal stability.3. An AB2monomer4-fluoro-4’,4"-dihydroxy triphenyl methane was synthesized. Through the homopolymerization of the monomer, a hyperbranched poly(phenylene oxide)(HPPO) with terminal phenolic groups was prepared. Terminal phenolic groups of HPPO were epoxidized and capped to afford epoxidized hyperbranched poly(phenylene oxide)(EHPPO) and end-capped hyperbranched poly(phenylene oxide)(CHPPO), respectively. Investigation of curing kinetics shows that additionof EHPPO into DGEBA make the curing process easier. Incorporation of EHPPO into DGEBA can increase the crosslinking density, increase free volume content, and decrease dielectric constant of the cured resin. Both EHPPO and CHPPO were used to toughen DGEBA and decrease its dielectric constant. Hybrids with EHPPO have better thermal properties, higher tensile and flexural strength, whereas, hybrids with CHPPO have higher impact strength and lower dielectric constant. |
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