基于嵌段共聚物自组装的具有单分散纳米分离孔道温度敏感分离膜的设计

The temperature-sensitive membranes based on poly(N-isopropylacrylamide)(PNIPAAm) show attractive application prospects in many fields. However, The responsive properties of temperature-sensitive membranes prepared by conventional approach are far beyond the reach of application because of the wide distribution of pore size and the difference of PNIPAAm chain length and density on membrane pore surface. In this project, the amphiphilic polystyrene(PS)-block-PNIPAAm copolymers with specific block ratio and narrow molecular weight distribution are designed and synthesized by atom transfer radical polymerization. The nano-porous PS-b-PNIPAAm temperature-sensitive membranes with monodisperse pore size and highly consistent of PNIPAAm distribution on pore surface are prepared by the method of selective swelling-induced pore-making process based on self-assembly of block copolymers. Compared to other methods to produce porous materials with well defined nanopores based on block copolymers, the selective swelling-induced pore-making process possesses synergic advantages that include extreme simplicity, good controllability, involvement of no chemical reactions, no weight loss,etc. The nano-porous PS-b-PNIPAAm membrane is combined with conventional separation membranes, and the temperature-sensitive composite membranes with PS-b-PNIPAAm temperature-sensitive layer on membrane surface are built. When the temperature changes, all the nanopores of PS-b-PNIPAAm layer show highly consistent and nano-level response behavior. Compared with the conventional temperature-sensitive membrane, the composite temperature-sensitive membranes have great advantages in response speed and separation accuracy. This method based on self-assembly of block copolymers is expected to develop into a universal method for preparing high performance temperature-sensitive membrane and expected to promote the process of temperature-sensitive membrane applications.

基于聚N-异丙基丙烯酰胺（PNIPAAm）的温度敏感分离膜在许多领域显示出诱人的应用前景。但传统方法制备的温度敏感膜由于膜孔尺寸及孔表面PNIPAAm分子链长度和密度不一致，响应性能远达不到应用的要求。本课题利用原子转移自由基聚合方法，设计、合成具有特定嵌段比、窄分子量分布的PS-b-PNIPAAm两亲嵌段共聚物，在嵌段共聚物自组装的基础上，采用一种简单易行，可控性好，无化学反应和质量损失的方法- - 两亲性嵌段共聚物选择性溶胀成孔法，设计一种孔径分布单一，孔表面PNIPAAm分布高度一致的纳米级多孔温敏薄膜。将该温敏薄膜与传统多孔分离膜相结合制备温度敏感复合膜。在温度变化时，温敏功能层将进行纳米级别的响应，所有膜孔的响应过程完全一致，与传统温度敏感分离膜相比，该方法制备的膜在响应速度和分离精度上将显示出很大优势。该方法有望发展成制备高性能温敏膜的一种普适性新方法，并有力推动温度敏感膜的应用。

基于聚N-异丙基丙烯酰胺（PNIPAAm）的温度敏感分离膜在许多领域显示出诱人的应用前景。但传统方法制备的温度敏感膜由于膜孔尺寸及孔表面PNIPAAm 分子链长度和密度不一致，响应性能远达不到应用的要求。本课题着眼于提高基于温度敏感膜的温度响应性能和分离性能，以嵌段共聚物选择性溶胀成孔法为主要方法，开展了深入系统的研究。首先以N,N-二甲基甲酰胺（DMF）为溶剂，以偶氮二异丁腈（AIBN）为引发剂，通过可逆加成断裂链转移法，制备PS-b-PNIPAAm嵌段共聚物。结果表明，嵌段共聚物的分子量Mn=26746g/mol，PDI=1.283，PNIPAAm的嵌段比小于50%，与选择性溶胀成孔方法所需的嵌段共聚物的结构基本相符。其次，将PS-b-PNIPAAm嵌段共聚物通过在硅片上旋涂的方法得到PS-b-PNIPAAm薄膜，并探讨了退火条件对该嵌段共聚物薄膜的分相行为的影响，结果表明：延长退火时间、采用嵌段共聚物的良溶剂溶解共聚物、选择合适的退火温度有助于PS-b-PNIPAAm薄膜有序结构的出现。最后利用涂覆的方法将PS-b-PNIPAAm涂覆在商用PVDF膜上，利用选择性溶胀成孔的方法，得到了上层是介孔功能层下层是PVDF商用膜支撑层的复合膜。通过调节溶剂种类、退火时间、溶胀时间、溶胀温度等条件，实现膜孔道的精密调控，对所得复合膜的性能进行了探讨。结果表明：延长溶胀时间、提高溶胀温度、选用PS-b-PNIPAAm良溶剂溶解并短时间退火、选择与PNIPAAm嵌段有良好亲和力的溶剂进行溶胀，有助于复合膜功能层呈现出均匀有序的孔道，且孔道逐渐增大。随着选择性溶胀成孔过程的进行，膜表面的PNIPAAm含量逐渐增多，膜表面亲水性逐渐提高，膜分离的温度敏感性更加显著。初步探讨了该复合膜的分离性能，结果表明，由于孔道的均匀有序和膜表面电荷作用，该复合膜对牛血清蛋白和溶菌酶都表现出100%的截留率。具体分离性能正在深入研究当中。与传统温度敏感膜的制备方法不同，该致孔方法操作方便，不涉及化学反应，没有质量损失，没有二次污染，具有较高的实际应用价值和发展潜力。所制备的膜表现出较好的温度响应性能，并且在蛋白质分离方面表现出良好的分离性能。研究成果有望推动温度敏感膜的开发和应用。