Preparation And Properties Of Liquid Crystalline Polyarylate Containing Naphthalenediformic Acid

Liquid crystalline polyarylate(LCP)is a kind of important special engineering plastic with outstanding thermal and mechanical properties,which is widely used in aerospace,military and electrical fields.LCP,which shows high strength,modulus and glass transition temperature(T_g)simultaneously,is composed of ester bond linking aromatic ring with high rigidity.However,the molecular backbone with high rigidity also leads to some processing problems,including high melting temperature(T_m)and large melt viscosity.Therefore,it is necessary to design the molecular structure of LCP in order to reduce T_m and melt viscosity.In this paper,4-hydroxybenzoic acid(HBA),4,4'-dihydroxybiphenyl(BP)and 1,4-dicarboxybenzene(TA)were used as the main chain structure of LCP,and the monomer 2,6-naphthalene dicarboxylic acid(NDA)with a kinded structure was introduced into the backbone.With the introduction od NDA,the linear structure of the rigid molecular chain was disrupted to a certain extent,and the regularity of the molecular backbone was reduced,endowing LCP with improved processability.In order to further improve the thermal stability and thermo-mechanical properties of LCP as well as prevent the product from darkening,antioxidants were added to HBA/BP/TA/NDA to increase polymer stabilization in high-temperature environments.In this paper,the influence of the introduction of nonlinear monomer(NDA)and antioxidants(1098,1010 and S9228)on the structure and properties of LCP was systematically studied,and high-performance liquid crystalline polymers with excellent processability and thermal stability were obtained.The main contents of this paper are as follows:(1)A series of novel LCP based on HBA,BP,TA and NDA was prepared by one-step melt polycondensation.LCP exhibits typical nematic schlieren texture,and the introduction of nonlinear monomer NDA changes the crystal form of LCP from pseudohexagonal to orthorhombic.Compared with the high T_m(>400?)of LCP without NDA,the T_m of LCP-NDA5 reduces to 350? with a minimum melt viscosity of 6.4×10~3 Pa·s,which significantly improves machinability and maintains excellent thermo-mechanical properties at 200?.(2)The effects of the introduction of blocked phenolic antioxidants(1098,1010)and phosphite ester antioxidant(S9228)on the performance of LCP were explored.The results show that LCP-NDA5 with the introduction of antioxidants exhibits stable liquid crystalline phase and improvement of the degree of crystallinity by 2-8%.At the same time,the LCP-NDA5 film shows excellent dilution effect and obvious internal fiber structure.The thermal stability of LCP-NDA5 was both improved by two kinds of antioxidants,among which phosphite ester antioxidants(S9228)had the most significant effect.The initial thermal decomposition temperature(T_d^5%)of LCP-NDA5-S9228 is increased from 458.5? to 506.7?.The residual carbon rate at 600?(Yc@600?)is increased from 48.32%to 52.81%.It is worth noting that the introduction of antioxidants has a significant effect on the thermo-mechanical properties,and the T_g of LCP-NDA5-S9228 is 22.5? higher than that of pure LCP-NDA5.In conclusion,LCP-NDA5-S9228 containing antioxidant of S9228 has great application prospect in high temperature environment.