AbstractCompared with conventional, solution‐phase approaches, solid‐state reaction methods can provide unique access to novel synthetic targets. Nanothreads—one‐dimensional diamondoid polymers formed through the compression of small molecules—represent a new class of materials produced via solid‐state reactions, however, the formation of chemically homogeneous products with targeted functionalization represents a persistent challenge. Through careful consideration of molecular precursor stacking geometry and functionalization, we report here the scalable synthesis of chemically homogeneous, functionalized nanothreads through the solid‐state polymerization of 2,5‐furandicarboxylic acid. The resulting product possesses high‐density, pendant carboxyl functionalization along both sides of the backbone, enabling new opportunities for the post‐synthetic processing and chemical modification of nanothread materials applicable to a broad range of potential applications.