苯乙炔基封端型聚酰亚胺树脂及复合材料的制备与性能研究

Preparation and Properties of Phenylethynyl-terminated Polyimide Resins and Composites

以4-苯基乙炔基邻苯二甲酸酐(PEPA)作为封端剂,以间苯二胺(m-PDA)和4,4′-(六氟异丙烯)二酞酸酐(6FDA)作为二胺、二酐单体,采用化学亚胺化法在N-甲基吡咯烷酮(NMP)中合成了一系列不同分子量的苯乙炔基封端聚酰亚胺预聚体(Pre-1~Pre-5),并对其结构和性能进行了表征分析。结果表明,由于空间位阻及扭曲结构的贡献,所制备的聚酰亚胺预聚体在一定分子量范围内具有良好的熔体流动性,其中分子量最低的Pre-1(理论分子量1601 g/mol)具有最低熔体黏度3 Pa·s(316℃)。固化后的聚酰亚胺树脂(PI-1~PI-5)具有优异的热稳定性,5%热失重温度(T_(5%))介于532~536℃之间,10%热失重温度(T_(10%))介于555~560℃之间,850℃时的残炭率介于54.3%~59.0%之间;随着预聚体分子量的下降,固化树脂的玻璃化转变温度(T_(g):316~338℃)呈上升趋势。以PI-1树脂为基体制备了碳纤维增强聚酰亚胺(CF/PI)复合材料,测试结果表明其具有良好的界面结合、高耐热性能(T_(5%):574℃,T_(10%):648℃,T_(g):359℃)以及较好的力学性能,其中弯曲强度为753 MPa,弯曲模量为54.0 GPa,层间剪切强度为51.2 MPa,冲击强度为90 kJ/m^(2)。

A series of phenylethynyl-terminated polyimide prepolymers(Pre-1~Pre-5)with different molecular weights were synthesized in N-methyl pyrrolidone(NMP)by chemical imidization using mphenylenediamine(m-PDA)and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)as the diamine and dianhydride monomers in the presence of 4-phenylethynyl phthalic anhydride(PEPA)as the end-capping agent.The structures and properties of these prepolymers were characterized and analyzed.The results showed that the prepared polyimide prepolymers had good melt fluidity in a certain range of molecular weights attributed to steric hindrance and twisted molecular structures,among which Pre-1 with the lowest molecular weight(calculated value of 1601 g/mol)exhibited the minimum melt viscosity of 3 Pa·s(316℃).The cured polyimide resins(PI-1~PI-5)displayed excellent thermal stability with 5%weight-loss temperature(T_(5%))of 532~536℃,10%weight-loss temperature(T_(10%))of 555~560℃and the char yields at 850℃of 54.3%~59.0%.The glass transition temperature(T_(g):316~338℃)of these cured resins increased gradually with the decrease of molecular weights of prepolymers.The carbon-fiber reinforced polyimide(CF/PI)composites were fabricated using PI-1 as matrix.The test results indicated that the composites obtained good interfacial combination and high heat resistance(T_(5%):574℃,T_(10%):648℃,T_(g):359℃),as well as satisfactory mechanical properties with flexural strength of 753 MPa,flexural modulus of 54.0 GPa,interlaminar shear strength of 51.2 MPa and impact strength of 90 kJ/m^(2).