Synthetic control of network topology and pore structure in microporous polyimides based on triangular triphenylbenzene and triphenylamine units

Abstract

Four new polyimide networks were prepared via a one-step polycondensation method by using tris(4-aminophenyl)amine and 1,3,5-tris(4-aminophenyl)benzene to react with pyromellitic dianhydride (PMDA) and naphthalene-1,4,5,8- tetracarboxylic dianhydride (NTDA), respectively. It was found that the topological structures and pore morphologies of the networks were tightly related to the geometrical shape of the net nodes, the molecular volume of the connecting struts, the reactivity of the monomers as well as the polymerization conditions. The results revealed that the reactions between triangular triamines and rod-like PMDA tended to form six-membered ring units, which were then extended to yield polyimide crosslinking networks, reflected by the complete disappearance of the endgroup signals in the FTIR and ¹³C CP MAS spectra, the significantly high thermal stability, large accessible surface area (818 cm² g⁻¹) and narrow pore size distribution centered at 4–8 Å. On the contrary, the low reactivity and steric bulky naphthyl group of the NTDA monomer led to the generation of branched or hyperbranched oligomers, which were further mutually crosslinked at a high temperature to produce the polyimde networks. In this way, a small amount of unreacted groups unavoidably remained, and the polymers exhibited a heterogeneous topological architecture, a broad pore size distribution and a low surface area of only 232 cm² g⁻¹. The influences of synthetic control and monomer structures on the pore morphologies and properties are investigated.