Photoresponsive Chain Collapse in Flexo-rigid Functional Copolymer to Modulate Self-healing Behavior
Synthetic systems mimicking natural self-folding process is attractive to impart multiple structural control over the polymer crosslinking and subsequent alteration of macroscopic self-healing properties. In that regard, polymers P1-P5 containing pendant photo-crosslinkable moieties are designed that undergo intra or inter-chain collapse to form diverse nanostructures. The shape and dimension of the nanostructures can be efficiently controlled by concentration, solvent compatibility and characteristics of the polymers. Photodimerization of coumarin moieties transforms the extended coiled chain of the polymer to uniform sized nanoparticles in dilute condition, while in the crowded macromolecular concentration regime, the polymer folds in nanostructures with polydisperse topologies that are far from condensed globule or partially swollen globule conformation. Scaling law exponents for polymer chain compaction suggests interchain collapse with rigid compact segments connected by flexible polymer chains and draws its analogy with elastomers. Such hardening of rigid segment as a consequence of photodimerization render the significant increase in the glass transition temperature (Tg) that can be reversibly controlled upon decrosslinking. Lastly, the structural variation of this class of polymers over self-healing is explored and crosslinked polymers shows photo-triggered nonautonomic & intrinsic self-healing behavior at ambient condition. This is an interesting approach to access photo-modulated self-healing system with low Tg polymers that shows coexistence of autonomic and non-autonomic self-healing pathways and may find its application in designing smart coating of photovoltaic device.