Solid-state topochemical polymerization is one way to synthesize novel macromolecular architectures with stereoregular chain structures. Topochemical reactions are attractive, green synthetic pathways in material design, since they occur in solvent-free conditions and in response to external stimuli, such ;as heat and light. For the first time, we have used the reversible [2 pi + 2 pi]-cycloaddition of a bioinspired bis-thymine monomer to topochemically synthesize a polymer. The polymer can be fully photo-depolymerized to the monomer and then reversibly and repeatedly photo-polymerized and photo-depolymerized. This is the first demonstration of complete photo-depolymerization and subsequent monomer recycling using this mechanism.