Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556.
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556.
Proc Natl Acad Sci U S A. 2021 Sep 14;118(37). doi: 10.1073/pnas.2022204118.
Polymers of intrinsic microporosity (PIMs) have shown promise in pushing the limits of gas separation membranes, recently redefining upper bounds for a variety of gas pair separations. However, many of these membranes still suffer from reductions in permeability over time, removing the primary advantage of this class of polymer. In this work, a series of pentiptycene-based PIMs incorporated into copolymers with PIM-1 are examined to identify fundamental structure-property relationships between the configuration of the pentiptycene backbone and its accompanying linear or branched substituent group. The incorporation of pentiptycene provides a route to instill a more permanent, configuration-based free volume, resistant to physical aging via traditional collapse of conformation-based free volume. PPIM-ip-C and PPIM-np-S, copolymers with C- and S-shape backbones and branched isopropoxy and linear -propoxy substituent groups, respectively, each exhibited initial separation performance enhancements relative to PIM-1. Additionally, aging-enhanced gas permeabilities were observed, a stark departure from the typical permeability losses pure PIM-1 experiences with aging. Mixed-gas separation data showed enhanced CO/CH selectivity relative to the pure-gas permeation results, with only ∼20% decreases in selectivity when moving from a CO partial pressure of ∼2.4 to ∼7.1 atm (atmospheric pressure) when utilizing a mixed-gas CO/CH feed stream. These results highlight the potential of pentiptycene's intrinsic, configurational free volume for simultaneously delivering size-sieving above the 2008 upper bound, along with exceptional resistance to physical aging that often plagues high free volume PIMs.
具有本征微孔结构的聚合物（PIMs）在推动气体分离膜的极限方面表现出了很大的潜力，最近重新定义了各种气体对分离的上限。然而，许多这类膜的渗透性仍然随着时间的推移而降低，这消除了这类聚合物的主要优势。在这项工作中，研究了一系列与 PIM-1 共聚的五并苯基 PIMs，以确定五并苯骨架的构型与其伴随的线性或支化取代基之间的基本结构-性能关系。五并苯的掺入为注入一种更持久的、基于构型的自由体积提供了一种途径，通过传统的构象型自由体积的坍塌来抵抗物理老化。具有 C 形和 S 形骨架以及支化异丙氧基和线性丙氧基取代基的共聚物 PPIM-ip-C 和 PPIM-np-S 分别表现出相对于 PIM-1 的初始分离性能增强。此外，观察到老化增强的气体渗透性，这与纯 PIM-1 随老化经历的典型渗透性损失形成鲜明对比。混合气体分离数据显示，相对于纯气体渗透结果，CO/CH 选择性增强，当从 CO 分压约 2.4 增加到约 7.1 atm（大气压）时，混合气体 CO/CH 进料流的选择性仅下降约 20%。这些结果突出了五并苯固有构型自由体积的潜力，它可以同时提供尺寸筛分，超过 2008 年的上限，同时具有对高自由体积 PIMs 经常存在的物理老化的出色抵抗力。
