polyimines

Polyimines, or polyimine polymers, are polymers that feature imine (C=N) linkages in their main chain or side chains. These imine bonds are typically formed by condensation between amine groups and carbonyl compounds such as aldehydes or ketones. As a result, polyimines often behave as dynamic covalent polymers whose bonds can reversibly form and break in response to chemical or environmental conditions.

Most common synthesis proceeds by Schiff base polymerization: the condensation of multifunctional amines with dialdehydes to give networks or linear polymers containing repeating imine units. Other routes include stepwise condensation under acid catalysis, or post-polymerization modification to introduce imine linkages. Imine bonds can be reduced post-synthesis to more stable secondary amines if greater hydrolytic stability is required.

Key properties depend on the substituents and architecture. Imine bonds confer pH- and moisture-sensitivity, enabling recyclability, self-healing, or stimuli-responsive behavior. The materials can form crosslinked networks with tunable mechanical properties, and their optical and thermal characteristics can be adjusted through backbone rigidity and conjugation.

Applications span recyclable plastics, smart coatings, responsive membranes and sensors, and catalytic or adsorptive materials. In biomedicine and drug delivery, degradable polyimines have been explored as transient carriers that release cargo under physiological conditions, while in energy and environmental technologies they are investigated for separations and capture processes.

Challenges include hydrolytic instability of imine bonds under humid conditions and broad variability in mechanical performance. Strategies to mitigate these issues include using more stable substituents, incorporating rigid or conjugated backbones, and converting imines to amines after polymerization.