Study On Multifunctional Epoxy Resins Modified By Poly(Arylene Ether Nitrile)s Containing Phthalazinone Moieties

Epoxy resins are a kind of very important thermosetting resin, especially tetraglycidyl-4,4’-diaminodiphenylmethane/4,4’-diaminodiphenylsulfone (TGDDM/DDS) system, used as matrix resins for high-performance fiber-reinforced composites in aerospace because of its high strength, good cost/performance ratio and excellent heat-resistance property. However, epoxy resins have poor damage tolerance due to the high cross-link density, which limits their use for some advanced applications. Incorporating thermoplastics into epoxy resins is an effective method to increase the toughness of epoxy resin without sacrificing their strength. Poly (arylene ether nitrile) (PEN) is a tough, semicrystalline high-performance engineering thermoplastic with outstanding thermomechanical properties. However, the poor solubility due to its semicrystalline nature and immiscibility with epoxy resin restrict their use as a modifier for epoxy resins. In the open literature, there are few reports about use of PEN as a modifier. Poly (arylene ether nitrile)s containing phthalazinone moiety (PPEN)s own outstanding thermal and mechanical properties with good solubility. They can be dissolved in polar aprotic solvents at room temperature, and also can be mixed with epoxy resins by solution blending. In this paper, PPENs are used to modify TGDDM/DDS system. It is expected to improve the impact strength of epoxy resin without decreasing the thermal properties and modules acutely.First, an epoxy resin based on the tetraglycidyl 4,4’-diaminodiphenyl-methane (TGDDM)/bisphenol A type novolac(F-51) with 4,4’-diaminidiphenysulfone (DDS) as curing agent has been modified by poly (phthalazinone ether nitrile ketone)(PPENK), having a glass transition temperature (Tg) about 280℃, by solution blending. The blends were measured by differential scanning calorimetry (DSC) with different heating rate before curing. The results suggested that the addition of PPENK did not affect the curing reaction of epoxy resins when the content of PPENK was below 20 wt%. The thermal and mechanical properties were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), flexural, impact strength and the critical stress intensity factor tests. The interaction between the PPENK and epoxy resin had been investigated by differential scanning calorimetry (DSC), FT-IR and dynamic mechanical analysis (DMA). These interactions gave good compatibility between PPENK and epoxy resin. So that, any phase separation had not been detected by DMA and scanning electron microscope (SEM). Beyond that, the interaction could also bring benefits to the thermal and mechanical properties. Compared with the neat epoxy resin, the maximum of impact strength was 11.4KJ/m2 by the addition of 10 phr PPENK, with an increment of 110%.A series of novel soluble phthalazinone-based copoly(aryl ether nitrile)s (PPBENs) were successfully synthesized by the nucleophilic substitution reaction of 2,6-difluorobenzonitrile(DFBN) with varying mole proportions of 4-(4-hydroxylphenyl)-2,3-phthalazin-1(2H)-one (DHPZ) and 4,4’-dihydroxybiphenyl (BP). The glass transition temperature was found to increase with increasing the DHPZ unit concentration in the copolymer main chain, ranging from 222 to 293℃. The TGA results showed that all the copolymers had 5% weight loss temperature up to 521℃ and the high char yield above 65% at 800℃ in nitrogen atmosphere, and the apparent activation energy value of thermal decomposition was about 200.6KJ/mol. Most of the obtained copolymers were soluble in common polar aprotic solvents, involving NMP, DMF, DMAc and chloroform etc. at room temperature. When the mole proportion of DHPZ and BP was 2:8, copolymer exhibited the best mechanical properties which were measured by using film samples, with tensile strength and elongation at break up to 137MPa and 15%, respectively. In conclusion, the obtained copolymers possessed excellent comprehensive performance.Then, PPBENs were used to modify the TGDDM/DDS system. A series of PPBENs modified epoxies blends were prepared by solution blending. The DSC results suggested that the addition of PPBENs did not affect the curing reaction of epoxy resins when the content of PPBEN was below 20 wt%. The thermal and mechanical properties and the micromorphology of the cured blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), parallel plate rheometry, mechanical property tests and scanning electron microscope (SEM) analysis, respectively. The rheological results indicated that the incorporation of thermoplastic PPBEN increased the viscosity of blends, and the gelation time of the blends was shortened. When content of PPBEN lower than 10 wt%, the viscosity of blends was lower 0.8Pa·s. The blends still had the good performance of processibility. The DMA results indicated that the glass transition temperature of blends was above 250℃. The no-notched impact strength of the cured blend with 15% PPBEN was up to 16.7KJ/m2, high about 104% than that of pure epoxy resin without sacrificing their modulus due to a specific sea-island structure. All the blends showed two-phase morphology characterized by DMA and SEM. The size of thermoplastic morphology was only 70-80nm, much less than that of commonly used thermoplastic, due to the special segment structure of PPBEN.