【作者】 李海瑞；

【导师】 樊君；

【作者基本信息】 西北大学 ， 化学工程， 2008， 博士

【摘要】 聚酰亚胺（Polyimide，简称PI）具有非常优异的耐热性、耐辐射性、耐化学性，良好的电绝缘性和力学性能等，现已广泛应用于航空、航天、电子、化工、机械等领域。现代科学技术的飞速发展对材料的种类和性能提出了更高的要求，各种杂化材料应运而生。杂化材料的特点是综合了各组分的优势，并起多功能的作用。聚酰亚胺在杂化材料的制备中有其独特之处，从而受到格外关注。本研究围绕聚酰亚胺薄膜的硅杂化改性主要展开了4个方面的工作：第一，聚酰胺酸（PAA）的合成与热亚胺化工艺条件确定。采用两步法合成（HQDPA-ODA）型聚酰亚胺。合成聚酰胺酸的优选工艺条件为：将单体二酐逐次加入二胺的溶液中，单体比为1．01：1，溶液固含量为10％，反应温度为10℃，反应时间为6h。热酰亚胺化工艺条件为：在80℃、150℃、240℃、280℃分别维持1h、1h、1h和0．5h。采用此工艺制备的薄膜经元素分析和红外分析可知已经基本亚胺化完全。采用热失重（TGA）分析薄膜热酰亚胺化动力学机理，得出酰亚胺化过程为两步一级动力学反应，快速阶段的活化能为38．14 kJ·mol^-1，慢速阶段的活化能为37．99 kJ·mol^-1，较为相近，速率常数的不同与活化能无关。快速阶段的指前因子A为172．31S^-1，慢速阶段的指前因子A为22．08S^-1，指前因子是导致快慢两个阶段速率常数降低的主要因素。第二，聚酰亚胺／SiO₂无机杂化膜的制备及硅偶联剂对聚酰亚胺／SiO₂杂化膜性能的影响。以正硅酸乙酯为无机前驱体，采用溶胶-凝胶法制备了聚酰亚胺／SiO₂无机杂化膜。结果表明，随着SiO₂含量的增加，杂化膜的热稳定性有所提高，但热分解温度的升高不是很明显。10％SiO₂含量的杂化膜，断裂伸长率、模量和强度分别比纯PI膜高32．5％、31．3％、26．1％，但SiO₂含量的进一步增大，杂化膜的各项力学性能均有所下降。扫描电镜显示SiO₂的团聚引起的应力集中，是造成膜的强度降低的主要原因。为提高聚酰亚胺和SiO₂两相的相容性，在杂化膜中添加分子间偶联剂GOTMS。SiO₂颗粒的团聚现象得到了有效抑制，10％SiO₂含量的杂化膜中，粒径从1-1．5μm减小到400nm左右，20％SiO₂含量的膜中，粒径也大大减小。较未添加偶联剂之前杂化膜的热稳定性降低，在10-25℃之间。同未添加GOTMS相比，纯PI膜和10％SiO₂含量的膜强度下降，20％、30％SiO₂含量的杂化膜强度增大。杂化膜的模量降低，断裂伸长率降低。同时添加分子间偶联剂GOTMS和分子内偶联剂APrTEOS以后，有机无机相相容性进一步提高，10％SiO₂含量的杂化膜中，粒径从1-1．5μm减小到100nm左右，20％和30％SiO₂含量的膜中，颗粒状SiO₂基本消失。杂化膜的热分解温度Td降低明显，都在120℃以上。纯PI膜和10％SiO₂含量的膜强度下降，20％、30％SiO₂含量的杂化膜强度增大。模量减小，断裂伸长率降低。但与相同SiO₂含量的只添加GOTMS的杂化膜相比，模量减小，断裂伸长率增大。第三，聚酰亚胺．聚硅氧烷嵌段杂化膜的制备与性能。为了改善刚性、半刚性聚酰亚胺-聚硅氧烷嵌段共聚物的可加工性等，本研究设计并合成了聚酰胺酯．聚硅氧烷嵌段共聚物，该共聚物较传统的聚酰胺酸-聚硅氧烷嵌段共聚物具有更高的溶解性和可加工性。实验证实这一合成路线的可行性。对合成的嵌段共聚物的热稳定测试表明，材料仍具有较高的热稳定性，热分解温度都在550℃以上，较聚酰亚胺降低不大，22～37℃。对制备的聚酰胺酯-聚硅氧烷共聚物亚胺化前后的形态进行研究发现，聚酰胺酯共聚物在固化过程出现了微相分离，并且相分离区有垂直于膜表面的趋势，随着硅氧烷含量的增大，相分离的区域增大，在PDMS=20wt％的膜中发现了完全从连续相分离出来的球形颗粒。亚胺化以后形成的PI-PDMS共聚物相分离进一步增大，结构更加疏松，形成了两相互穿的聚合物网络，此种结构是理想的渗透汽化膜分离材料的结构。最后，对经过无机SiO₂改性和有机硅氧烷嵌段改性的聚酰亚胺杂化膜进行了渗透汽化性能测试。65℃分离85％乙醇／水体系时，聚醚酰亚胺（HQDPA-ODA）具有优先透水的性质，渗透通量可达到60．7 g／m²·h，分离因子59。聚酰亚胺膜在这一体系中，乙醇和水的透过表观活化能分别为33．6、76．2KJ／mol。聚酰亚胺／SiO₂杂化膜渗透通量较纯聚酰亚胺膜减小，分离因子升高。乙醇水透过杂化膜的表观活化能随SiO₂含量的增大而增大。经聚二甲基硅氧烷嵌段改性的聚酰亚胺膜在分离乙醇水时表现了良好的分离性能。在分离因子仍就很高的情况下，通量增大到原来的2～3倍。更多还原

【Abstract】 Polyimides （PI） have unique physicochemical properties: strong resistance to high temperature, radiation and chemical resistance, good mechanical strength, superior insulation properties, etc. The properties make polyimides valuable materials which can be used widely in different branches of industry, such as aviation, aerospace, electron, chemical industry and mechanical industry, etc. With the rapid development of modern science and technology some new materials with special properties are required. Hybrid materials emerged in this context. Hybrid materials which combine the advantages of their components can play the multifunctional role. For its unique properties polyimide hybrid materials received much attention. In this dissertation focusing on the hybrid modification with silicon compounds four studies were conducted.1. Determination of process conditions in Synthesis of polyamic acid and thermal imidization. The polycondensation of HQDPA-ODA polyimide were carried out in two stages. The optimum conditions for synthesis of polyamic acid are present as: HQDPA was added into ODA solution in batches, the molar ratio of HQDPA: ODA is 1.01:1, the solid content of this solution is 10wt%, reaction temperature is 10℃, and reaction time is 6h. Imidization was carried out in successive isothermal steps of 1 h for each 80, 150, 240℃, and 0.5h for 280℃. Fourier transfer infrared spectrophotometer （FT-IR） spectra and element analysis show that the film nearly finished a complete imidization. The reaction mechanisms and kinetic models for imidization were investigated by Thermogravimetric analysis （TGA）. The results suggest the imidization is a first, two step reactions. Activation energies for the fast process and the second slow process are 38.14 KJ/mol and 37.99 KJ/mol, respectively. Preexponential factors for the two steps are 172.31S^-1 and 22.08S^-1, which account for the difference in the rate constants.2. Preparation of polyimide/SiO₂ hybrid membranes and the effects of coupling agents on properties of the polyimide/SiO₂ hybrid membranes. Polyimide and polyimide/SiO₂ hybrid membranes were prepared via sol-gel process while Tetraethyl orthosilicate（TEOS） was added as inorganic precursor. Results show the thermal stability of PI/SiO₂ increases with the increasing of SiO₂ content, but this increase of Td is not remarkable. Elongation at break of the hybrid membrane containing 10wt% SiO₂ increases by 32.5%, strength 31.3%, and modulus 26.1% in contrast to that of the pristine PI. But more introduction of SiO₂ decreases the strength and modulus. Scanning electron microscopy （SEM） indicates that the decrease may be caused by the aggregation of silica, which would lead to stress concentration at the silica/PI interfaces.In order to improve the compatibility between polyimide and silica, inter-molecular coupling agent, GOTMS was introduced into PI/SiO₂ hybrid membranes. The aggregation of silica particle was efficiently prevented. The particle size in PI/SiO₂ hybrid membranes containing 10wt% SiO₂ was reduced from 1～1.5μm to 400nm, and that containing 10wt% SiO₂ reduced greatly too. The Td of PI/SiO₂ hybrid membranes decreased by 10～25℃after the introduction of GOTMS. The strength of pristine PI and hybrid membranes containing 10wt% SiO₂ declined while that containing 20wt% and 30wt% SiO₂ heightened. The elongation at break and modulus lowered.After the introduction of inter-molecular coupling agent GOTMS and intra-molecular coupling agent APrTEOS at one time, the compatibility between organic and inorganic phase was further improved. The particle size in PI/SiO₂ hybrid membranes containing 10wt% SiO₂ was reduced from 1～1.5μm to 100nm, and particle in that containing 20wt% and 30% SiO₂ nearly disappeared. The Td of PI/SiO₂ hybrid membranes decreased markedly by 120℃or more. The strength of pristine PI and hybrid membranes containing 10wt% SiO₂ declined while that containing 20wt% and 30wt% SiO₂ heightened. The elongation at break and modulus lowered. However comparing with these hybrid membranes with equal SiO₂ the elongation at break lowered, and modulus rise.3. Preparation and characterization of polyimide-block-polydimethylsiloxane （PI-PDMS）. To facilitate the processibility of PI-PDMS, we designed and synthesized polyamic acid ester-block-polydimethylsiloxane which has a better solubility and processibility than polyamic acid-block-polydimethylsiloxane. Experiments proved the synthesis route is feasible. Comparing with the pristine PI Td of PI-PDMS decreased mildly by 22～37℃, but still was above 550℃. Investigation of morphology of PAE-PDMS and PI-PDMS provided that micro-phase separation in the course of solidification, and that the micro-phase separation had a tendency to be vertical with surface of membranes. The domain of phase separation became bigger with the increasing PDMS. When content of PDMS rise to 20wt% spherical particles isolated from the continuous matrix. The successive thermal imidization made the domain of phase separation bigger further and structure looser. An interpenetrating network polymer was developed which should be a promising membrane materials for pervaporation.4. Pervaporation performance of PI/SiO₂ and PI-PDMS membranes. In separation of 85wt% aqueous ethanol solution at 65℃the pristine PI had preferential permeability to water over ethanol, and exhibited a flux of 60.7g/m2·h and a separation factor of 59. The apparent permeation activation energy for ethanol and water was 33.6 and 76.2kJ/mol respectively. PI/SiO₂ hybrid membranes had lower flux and higher separation factors than the pristine PI. Apparent activation energy of water and EtOH through polyimide hybrid membranes increases with increasing of SiO₂. When PDMS was blocked in the PI, PI-PDMS membranes exhibited high separation performance. The flux became 2～3 times high than the pristine PI while separation factor is sill in a high level.更多还原