具有亲水聚合物刷的高通量共混超滤膜的制备、结构调控及抗污染机理研究

On basis of molecular design, The amphiphilic comb-like copolymers (PEG-g-SMA) with polyethylene glycol (PEG) chains grafted to poly(styrene-alt-maleic anhydride)(SMA) were synthesized via two routes. First, reversible addition-fragmentation chain transfer (RAFT) copolymerization of styrene(St) and maleic anhydride(Man) was performed in supercritical CO2 to synthesize alternating copolymer SMA, which subsequently was grafted with PEG by esterification reaction of anhydride groups and hydroxyl groups, aiming at preparation of amphiphilic copolymer PEG-g-SMA with a well-defined comb-like chain morphology. Second, the amphiphilic comb-like copolymers (PEG-g-SMA) were synthesized in supercritical CO2 used as the reaction medium by RAFT copolymerization of 4-PEG grafted styrene(PEG-g-St) and maleic anhydride. Moreover, PEG-g-St was obtained by Williamson reaction of 4-vinyl benzyl chloride and mPEG. For the comb-like copolymers PEG-g-SMA, The alternating structure was confirmed by 13C NMR analyses and the living character was checked by quantitative UV analysis of the dithiobenzoyl end group of the polymer chains. These amphiphilic copolymers were used to blend with PVDF in the preparation of polymric blend membranes by phase inversion method. Based on the analysis of membrane-forming thermodynamics and kinetics, the blend membrane structures were controlled via regulating the thermodynamics and kinetics of membrane-forming system. It was found that amphiphilic comb-like copolymer additives migrated to the membrane surface and accumulated and self-organized spontaneously in polymer brush structure on membrane surface during the course of phase inversion. The PEG brush on membrane surface notably improved the hydrophilicity and anti-fouling ability of PVDF blend membranes and significantly increased the PVDF blend membrane's pure water permeation (PWP) rate. In addition, some functional molecules or groups can be immobilized on membrane surface using the reactive groups in amphiphilic copolymers as spacer. PWP tests, contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to assess the impact of PEG-g-SMA structure, molecular weight and concentration on the performance and characteristics of blend PVDF membranes. XPS analysis and contact angle measurements and SEM and AFM images were used to investigate the migration of PEG-SMA and the relation between surface morphology and ultimate performance. Furthermore, It is shown, using particle image velocimetry (PIV), that the resulting movement of the PEG brushes on the surface of blend membrane induces mixing directly above the membrane surface and then reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on hydrophilic polymer brush has much broader implications.

通过超临界二氧化碳RAFT活性共聚和接枝改性，设计并合成主链为苯乙烯/马来酸酐交替共聚物SMA，侧链接枝聚乙二醇PEG的梳状两亲共聚物PEG-SMA；将其与聚偏氟乙烯PVDF共混，并利用相转化法制备表面具有PEG刷的高通量、抗污染的PVDF共混超滤膜。研究超临界二氧化碳体系RAFT活性共聚机理和反应条件等因素的影响，控制PEG-SMA具有特定结构和分子量；研究共混体系的相容性和相分离过程热力学与动力学规律，揭示梳状两亲共聚物的表面迁移和自组装机制；研究柔性PEG刷对膜表面二维流场的影响以及对浓差极化所致边界层的影响，揭示膜表面亲水聚合物刷的抗污染机理。研究梳状两亲共聚物链结构和两亲共混体系成膜热力学/动力学协同效应对两亲共混膜表面介观结构以及膜分离性能的影响规律，揭示表面刷状亲水层同时提高共混膜水通量和截留率的机制。利用两亲共聚物的反应性基团固载半乳糖苷酶，实现PVDF共混膜进一步功能化。

基于分子设计的原理，通过功能单体参与的自由基共聚，合成表面具有酸酐基、羟基和胺基等的功能性共聚物。研究了共聚机理，对共聚物结构和表面性质进行了分析表征，展开了进一步的功能化应用研究，特别是基于应用的表面再功能化研究。设计并合成聚乙二醇二丙烯酸酯/二乙烯基苯/甲基丙烯酸缩水甘油酯共聚物PDG，苯乙烯/马来酸酐交替共聚物SMA，侧链接枝聚乙二醇PEG的刷状两亲共聚物SMA-PEG；对PDG进行表面氨化改性，研究了其表面吸附性能，吸附符合准二级动力学方程，以化学吸附为主；将SMA和SMA-PEG等两亲共聚物与聚偏氟乙烯PVDF共混，并利用相转化法制备表面具有PEG刷的高通量、抗污染的PVDF共混超滤膜。研究两亲共聚物共混体系的相容性和相分离过程热力学与动力学规律，揭示刷状两亲共聚物的表面迁移和自组装机制；研究两亲共聚物共混体系成膜热力学/动力学协同效应对两亲共混膜表面结构以及膜分离性能的影响规律，发现了两亲共聚物亲水层能够同时提高共混膜水通量和截留率。利用共混膜表面两亲共聚物的反应性基团固载半乳糖苷酶，固定化酶膜活力可达13.5 U/cm2 膜,实现PVDF共混膜进一步功能化。设计并搭建了测试膜面流场特性的膜面流场测试系统，用于近膜面气液两相流强化膜面传质和控制膜污染的机理研究，实现了基于先进的PIV荧光粒子法同时获取近膜面气泡动力学特性和液相流场的流体力学特性的测试，研究膜污染机理。搭建了中试规模浸没式超滤水处理试验系统（膜生物反应器实验系统），用于分析帘式中空纤维膜组件膜面附近的流场特性，为后续的工程规模的膜污染实验研究奠定了实验基础。选用多相流欧拉模型与多孔介质模型耦合对浸没式中空纤维膜面气液两相流流场进行数值模拟，并通过PIV实验结果验证了耦合模型的正确性，为膜生物反应器技术的工程实践铺垫理论基础。