| Epoxy resins are one of the most important thermosetting resins, which are widely used in the field of aviation, spaceflight, architecture, insulation and matrix for high-performance composite, due to their outstanding properties in thermal stability, mechanical strength, adhesive strength and processibility. However, because of high cross-link density, poor properties such as brittle, low impact strength and fracture toughness, their further proliferations into other applications are limited. In this dissertation, a series of polyaryletherketone bearing different content pendant carboxyl groups were synthesized as toughening agent to modify epoxy resins. We issued on the change of the mechanical and thermal properties, morphology of the modified epoxy systems due to the length of molecular chain between two near carboxyl groups. Main contents and conclusions are as follows:(1) A series of polyaryletherkotone copolymers were synthesized via solution nucleophilic polycondensation reaction from phenolphthalein(PPH), phenolphthalein(PPL) and 4,4'-difluorobenzophenone(DFDPK) and characterized by FT-IR, GPC, DSC and TGA. The solubility and tensile property were also studied. The results revealed that all the copolymers with the number-average molecular weight (Mn) from 65000 to 83000 had a narrow molecular weight distribution. The copolymer possessed excellent thermal properties with a high glass transition temperature of above 220℃,5% thermal weight loss of 474℃. Furthermore, the glass transition temperature was slightly decreased with the increasing of PPL in the copolymer. The property of solvent resistant was strengthened because of the introduction of carboxyl groups. Tensile strength and tensile modulus of the copolymer increased firstly and became balanced with the increasing of carboxyl groups.(2) After the curing process of 110℃2h+140℃2h+170℃3h+200℃2h, the copolymer had completely inserted into the epoxy network according to DSC and DMA. The thermal and dynamic mechanical properties of the modified epoxy were examined via DSC, TGA and DMA. The results showed that thermal stabilities of the modified epoxy resins were enhanced compared with the neat epoxy resin and the increase of carboxyl contents was benefit to thermal properties. The value of tan 8 was decreased obviously duo to the introduction of copolymers, but increased with the carboxyl contents. The storage modulus of modified epoxy resins was increased, however, it decreased in the glass state and increased in the rubbery state with the increase of carboxyl contents. According to the experienced formula, cross-link density of the modified epoxy resins were increased with the carboxyl content.(3) The effect of the length of molecular chain between two near carboxyl groups on mechanical properties and morphology were researched. It was found that flexural strength of modified epoxy changed a little and the flexural modulus decreased slightly while the flexural stain of at break was improved. The addition of the copolymer was benefit to the improvement of fracture toughness and the value of KIC and GIC decreased when the length between two near carboxyl groups got shortened. The change of notched impact strength was similar to fracture toughness. It was clearly observed from scanning electron microscope(SEM) that all the system were homogeneous. The fracture surface of modified epoxy resins possessed typical characteristics of ductile fracture and it tended to brittle fracture with the increase of carboxyl groups in the copolymer. |
