Epoxy Resins Toughened By Copoly(Phthalazinone Ether)S Containing Carboxyl Groups

As the most prominent thermo setting resins, the epoxy resins have been widely used as aerospace, insulation materials in the recent few decades for possessing a combination of interesting properties such as excellent mechanical properties, thermal stabilities, corrosion resistance and electrical insulation properties. However, the proven disadvantages of lacking toughness have restricted its application in engineering and structural material fields. Therefore, toughening epoxy resins while maintaining their several merits has been an extremely urgent project that attract significant attention of researchers. On the basis of their comprehensive study, herein two kinds of high performance copoly(phthalazinone ether sulfone/ketone)s containing pendent the carboxyl groups,which had twisted non-coplanar phthalazione structure in the polymer backbone to give the polymers heat resistance and solubility and reactive pendent carboxyl groups to react with epoxy resin, were designed and synthesized to modify the mechanical properties of commercial AG80epoxy resins. The main research conclusions are summarized as follows:A series of copoly(phthalazinone ether sulfone)s (PPES-P) and copoly(phthalazinone ether ketone)s (PPEK-P) containing pendent carboxyl groups were prepared designed from phenolphthalin(PPL) and4-(3-chloro-4-hydroxylphenyl)(2H)-phthalazin-l-one (DHPZ) with bis(4-chlorophenyl) sulphone (DCS) or bis(4-fluorophenyl)ketone (DFK) via solution polycondensation reactions. FT-IR,1H-NMR, TGA and DSC instruments were conducted to confirm the structures of the resulting polymers and evaluate the corresponding properties. The results showed that the two types of polymers are all amorphous and possess excellent thermal and mechanical properties. The glass transition temperatures (Tgs) of PPES-P series are greater than260℃, while the temperatures of the95%retention of weight lying between440～467℃; The Tgs of PPEK-P series are between235-255℃, and the temperatures of5%mass loss are higher than56%, which are better than the PPES-P counterparts on the contrary. Regularly, the overall thermal and mechanical properties increased with the increasing contents of phthalazinone moieties in the backbone.Non-isothermal DSC test was conducted to study the reaction of PPES-P with and AG80resins and DDS as well as the curing behavior of PPES-P/AG80/DDS blending system. The results indicate that the carboxyl group of PPES-P11exhibits adequate reactivity with epoxy moieties, and couldn’t react with DDS. The reaction kinetics of the blending system was investigated by Kissinger method and Ozawa method, respectively. The results show that the introduction of PPES-P resin lowers the energy barrier of the curing reaction, and could promote the crosslinking procedure efficiently. Finally, the optimal curing process was chosen as130℃lh+160℃2h+190℃3h+210℃via evaluating the combinative properties of the networks after curing.Under the optimal curing condition, the influence of the polymer addition dosages and the structural nature of PPES-P on the mechanical properties and thermal properties of modified epoxy resin were concerned. The results reveal10-phr PPES-P13/AG80/DDS presents the best toughness. Its notched impact strength reaches3.22KJ/m2, which was56%higher than that of AG80/DDS, with the slight decline of its flexural strength and no distinct change of thermal stability. PPEK-P/AG80/DDS modified resin system also displays the analogous toughening results.10-phr PPEK-P13/AG80/DDS has the maximum value of notched impact strength of3.16KJ/m2for43%higher than neat resins. Simultaneously, its flexural strength modulus of3.9GPa and thermal properties are all enhanced. Scanning electron microscopy showed that all the AG80blending systems are homogeneous structure, indicating the reaction between carboxyl pendants and epoxy moieties indeed exists.