Structure–Conformation–Reactivity Relationships in Optically Active Schiff Base Polymers: Effects of Aromatic Linkage Geometry on Chiroptical Properties and Chemical Recyclability

ABSTRACT

Optically active Schiff base polymers were synthesized from ʟ‐alanine‐ and N ‐methyl‐ʟ‐alanine‐derived diamines with ortho ‐, meta ‐, and para ‐phthalaldehydes. Meta ‐ and para ‐linked NH polymers exhibited intense circular dichroism (CD) signals, indicating chirally fixed conformations, whereas ortho ‐linked and N ‐methylated polymers were CD‐inactive. Dynamic light scattering measurements suggested that only the CD‐active polymers formed folded and/or weakly associated structures in solution. Acid‐catalyzed hydrolysis showed pronounced structure dependence. Ortho ‐linked polymers were resistant to hydrolysis, whereas meta‐ and para‐linked polymers underwent clean depolymerization under mildly acidic conditions. The NH polymers hydrolyzed more slowly than the corresponding N ‐methylated analogs, likely due to reduced molecular mobility associated with conformational fixation. Furthermore, the para ‐linked polymer was successfully depolymerized and repolymerized, demonstrating closed‐loop chemical recyclability.