Introduction

Abstract

Ladder polymers represent a unique class of macromolecular architectures, where all the adjacent repeat units are connected by two or more bonds. Ladder polymers can be formed via 1) ladder polymerization, in which ring formation between monomers repeatedly occurs; 2) “zipping” of a linear precursor polymer containing pendant functional groups that cyclize with the neighboring repeat units to ladderize the polymer; 3) formation of double-stranded polymers via duplex polymerization or complexation. Despite the difficulties in the synthesis, characterization, and processing of ladder polymers, a variety of ladder polymers with diverse structures and properties have been reported. The structural and conformational rigidity often renders ladder polymers unusual properties that are unmatched by traditional single-stranded polymers, and some ladder polymers have enabled important applications. Looking forward, exciting opportunities exist on developing more selective, efficient, and controlled chemistry for ladder polymer synthesis, characterizing and analyzing ladder polymers in greater detail and across several length scales, discovering their extraordinary properties and behaviors, and translating the unique macromolecular features to macroscopic materials and advances in critical technologies.