Pore Network Percolation in Polymers of Intrinsic Microporosity Examined by Gaseous and Antimatter Probes

Synthesis of polymers with tailored properties requires an understanding of the underlying phenomena leading to these properties. Polymers of intrinsic microporosity (PIMs) are non-network polymers with a substantial guest-accessible free volume. Their BET surface areas have been reported to be as high as 1000 m²/g, and their porosity has led to the demonstration of some of the best membrane-based gas separations to date. However, it has been challenging to predict porosity in PIMs a priori, in part due to an incomplete framework for understanding the origins of porosity in these materials. Here, porosity in several archetypal PIMs is examined through the lens of a percolation model, whereby porosity in oligomers follows behavior expected for nonpercolated and percolated networks. Positron-based Doppler broadening spectroscopy is used to examine buried pores in samples whose pores are inaccessible to typical (nonantimatter) guests and demonstrate that buried pores are present in PIMs with nonpercolated pore networks. Taken together, the findings are in agreement with the contention that network percolation plays a critical role in pore accessibility in PIMs.