采用反相水性乳液法制备形貌可控的聚酰亚胺及其复合微球的研究

Polyimides (PIs) are known for high thermal stability, good chemical resistance, and excellent mechanical properties. Their microspheres are very useful for low dielectric constant films, ion exchange membrane, supports for catalyst, separation and purification, functional coatings, and so forth. Polymer microspheres are usually manufactured during polymer synthesis from a monomer, for example, in suspension, emulsion and dispersion polymerizations. The preparations of microspheres of vinyl polymers have been well fabricated by above mentioned methods. However, there are a few reports on the microspheres of non-vinyl polymers including PI. The purpose of this investigation is to manufacture PI and its composite microspheres with controllable morphology, through controlling the interaction relationship between interfacial thermodynamics and phase-separation dynamics of liquid droplet in solution. It provides the guidance to establish an emulsion system with stable interface. The aqueous inverse emulsion method has been discovered and will be used for this investigation. The aqueous inverse emulsion is composed by poly(amic acid) ammonium salts (PAAS) aqueous solution, non-ionic surfactants and N-alkanes. PI microspheres with different morphologies will be prepared by further imidization reaction of PAAS with acetic anhydride. The stability of emulsion with different compositions will be discussed. Due to the imidization reaction of PAAS and phase separation, the interface of emulsion will exhibit different stress state. Different structures and compositions of inverse emulsion will change the stress state and the final morphologies of PI microspheres. Based on their relative rules, the theory model will be established.

聚酰亚胺微球是集聚酰亚胺耐高低温，耐辐射，耐酸碱等优异综合性能和微球的功能性于一身的新型材料，具有烯烃类聚合物微球无法比拟的优异性能，在低介电常数高性能薄膜、离子交换、催化载体、分离纯化等领域中具有潜在的应用价值。项目通过设计调控反相乳液界面热力学和相分离动力学之间的相互关系，实现不同形貌的聚酰亚胺及其复合微球的可控制备。在该思路指导下，通过将聚酰胺酸三乙胺盐水性溶液为分散相，非离子表面活性剂为乳化剂，正构烷烃为连续相构筑反相水性乳液体系，并选用乙酸酐为固化剂制备聚酰亚胺微球。通过调整组成及含量研究乳液的稳定性，得到相对稳定的界面及条件控制范围。重点研究固化过程中由于聚酰亚胺固化反应及相分离引起的乳液界面受力状态的变化，通过调控乳液组成实现形貌可控的聚酰亚胺微球的制备。进一步通过研究微球形貌变化规律与界面作用的相互关系，建立相关的理论模型。

本项目通过系统研究聚酰胺酸盐反相乳液形成的条件，重点考察了水含量，固含量以及表面活性剂种类用量对乳液体系的稳定作用，结合调控乳化剂种类，HLB值及聚合物分子链结构等方法获得包括圆球，半球，陨石坑结构的微球等多种聚酰亚胺微球。进一步结合溶胶-凝胶法与反相乳液，通过调控相关参数制备了聚酰亚胺/二氧化硅复合微球，并对复合微球的内部组成和结构进行了详细研究。研究发现通过表面自由能的变化可解释聚合物微球形态的变化，在体系最小表面自由能的基础上所得到的聚合物微球的结构是由表面张力决定的，它控制着相分离液滴的最终的平衡形貌。亚胺化之前系统处于一个相对平衡的状态，引入固化剂以后，固化剂进入乳液滴内，引发化学亚胺化反应，这就破坏了原有的平衡状态，引发相分离。在相分离过程中，表面张力和表面自由能的变化会导致聚合物微球结构的改变。在此基础上，通过对乳液体系的界面设计，引入阳离子表面活性剂与非离子表面活性剂复配，成功制备了具有中空结构的聚酰亚胺微球。通过本项目的研究，制备了多种聚酰亚胺及复合微球，也为其他类似材料的微球制备提供了新思路，为进一步功能化进行一些有益的探索。