氟代低碳烃是有机氟材料等国家战略资源的关键原料，由于沸点低且易共沸，传统相平衡分离技术流程复杂、能耗高、损失大、污染严重。基于扩散控制的聚酰亚胺膜，选择性高，可打破相平衡制约，但氟代低碳烃分子远大于常规膜材料中自由体积空穴的尺寸，导致渗透系数低，严重制约工业应用。本项目提出立体大侧基改性形成局部空间位阻，增加刚性扭曲主链间距、减少结晶结构，提高自由体积和空穴尺寸，并通过侧基结构和取代度精细调控传质通道，与不同体系中渗透的氟代低碳烃分子实现尺寸匹配，设计合成系列高选择性、高渗透性含氟聚酰亚胺膜材料；系统研究铸膜新体系的相平衡热力学和相界面传质动力学，调控亚稳态区域宽度，促进铸膜液瞬时分相形成100nm级超薄无缺陷选择层，可控制备高选择性低阻力非对称复合膜。以上研究将为精细调控特种气体分离膜性能提供新的思路，国内外未见报道，对实现有机氟化工绿色可循环发展、推动国家战略资源高度自给具有重要意义。

Gaseous fluorinated hydrocarbons are the basic chemicals for national strategic resources such as fluoropolymers. They are usually low in boiling point and easy to form azeotropic mixture, so that their separation and purification using conventional phase equilibrium technologies are complex in process and intensive in energy consumption; moreover, the loss and the attached pollution should not be ignored. .Glassy polyimide membranes based on the diffusion-controlled permeation can operate without the restriction from phase equilibrium and have high selectivity to overcome the bottleneck. However, fluorinated hydrocarbons, since their molecular size is much larger than the usual permeable species, are very low permeable in the existing glassy polymer membranes, that is a serious constraint to the actual applications. .In this project, polymer modification with stereoscopic side groups is proposed for fluorinated polyimide to tune aggregation morphology and then enhance selective permeation for fluorinated hydrocarbons. In detail, stereoscopic side groups on an inflexible polymer backbone would repulse the other backbones in the neighborhood, reduce crystalline units, and improve the free volume; in this instance, the modified membrane materials would have more permeation channels for large-size gaseous molecules and more permeable for gaseous fluorinated hydrocarbons. Moreover, the mass transfer channels can be adjusted meticulously to fit for the permeated molecules in different mixtures waiting for separation by grafting various stereoscopic side groups with different substitution degree. .After material synthesis, the phase equilibrium thermodynamics and the phase interface mass transfer kinetics would be studied systematically for the new membrane casting system to direct the regulation for the metastable zone of membrane casting solution, with the intent to accelerate instantaneous phase inversion and then fabricate defect-free and ultrathin-skinned (<100 nm) asymmetric membranes. .In conclusion, this project would bring about new mechanisms and approaches for modulating membrane material properties precisely, which is very important to exploit the new application fields of membrane technology such as fluorine industries.