High Performance Of Polyfunctional Epoxy Resins: Control Synthesis And Applications

Due to the excellent mechanical and electrical properties, low shrinkage, and strong adhesion, epoxy resins are widely used in various applications, such as coatings, adhesives, structural composites, and electronic materials. However, the inadequate toughness, thermostability, and use temperature of DGEBA type epoxy restrict its wider applications. In order to address those issues, a series of control-synthesized polyfunctional epoxy resins, including hyperbranched epoxy and tetrafunctional epoxy, were prepared and used as modifiers for DGEBA matrix. When modified by hyperbranced epoxy, the cured materials show simultaneous improvements in tensile strength, impact strength, and glass transition temperature (Tg). When modified with the tetrafunctional epoxy, the cured materials not only show a Tg higher than 250? but also show good tensile strength and impact strength. Based on those results, the relationships between modifier structure and performance were explored, and mechanisms for the improvements were investigated. The main contents of the dissertation are shown below:1. A facile new method for preparing hyperbranched polymers with controlled structures were proposed for the first time. By taking advantage of competing reactions, hyperbranched polymers with controlled molecular weight (MW) and invariant degree of branching (DB) were easily obtained. AB2 monomers, which have alkyl bromide group and phenol group, were used in polymerization reactions. The competing reactions between substitution reaction and elimination reaction lead to a fast stabilization in MW, which can be achieved within 4 h. The fast stabilization made the reaction insensitive to the variations in reactor size, stirring rate and heat conduction, and also results in better controllability and scalability. Based on those controlled stystems, layer-by-layer and multilayer core-shell hyperbranched polyethers, which have programmable MW, almost invariant DB, and narrow MW distribution, were realized by batch feeding the same or different AB2 monomers.2. Serveral hyperbranched systems with tunable Tg were demonstrated. By taking advantage of competing reactions, a series of copolymers and binary blends of homopolymers with different compositions were obtained using copolymerization and physical blending, repectively. Copolymers show better tenability:Tg of copolymers as a function of monomer ratio can be fitted with Fox equation and the width of Tg (?Tg) is similar to that of homo-polymers. For binary hyperbranched blends, good miscibility can be ensured if both components have the same terminal groups; moreover, hydrogen bonding can indeed improve the miscibility and decrease ATg.3. Facile controlled synthesis of an epoxide-terminated hyperbranched aromatic polyether (EHBPE) was realized by using one-pot A2+B3 approach thanks to the competing reactions. When used as modifier for an epoxy curing system, non-phase-separated hybrids with simultaneous improvements in tensile strength, impact strength, modulus, and Tg were obtained. The hybrid with 5% EHBPE loading shows the optimum performace. Such excellent modification effect can be explained by the cavity toughening mechanism. More importantly, the toughening mechanisms for the non-phase-separated hybrids are outlined in detail for the first time.4. Four control-synthesized epoxide-terminated hyperbranched polyethers (EHBPEs) with different structure were obtained by varing monomer structure. When used as modifiers for epoxy curing system, both EHBPE-4C which has the lowest MW and stiffest backbone and EHBPE-IOC which has the highest MW and most flexible backbone show best overall perforamances. In contrast, the other two mofifiers are not very effective. Based on the obtained structure-property results, it appears that both backbone stiffness and the number of reactive terminal groups are important parameters in terms of designing a high performance hyperbranched modifier.5. High performance homopolymerized DGEBA epoxy was prepared. Among two catalytic systems,1MI and DMAP,1MI system is found to be more suitable for LCM (Liquid Composite Molding). Effects of 1MI concentration on mechanical properties of cured epoxy were studied. Optimum mechanical properties is observed at 8mol% 1MI concentration; however, its toughness and strength are inadequate for a high performance epoxy. Thus, the previously reported hyperbranched epoxy was thus added as modifier, which leads to simultaneous enhancements in tensile strength, impact strength, cross linking density, and Tg.6. A series of new tetrafunctional epoxy resins were synthesized through a three-step process. Cured hybrid epoxy materials with high Tg and excellent mechanical properties were realized by mixing tetrafunctional epoxy resins with DGEBA in desired ratios. Among those four tetrafunctional epoxy resins, EC4 is found to have the best performance. Compared with the widely used TGDDM, EC4 hybrids are superior in many aspects, including balanced mechanical properties, better processibility, and more cost effective.