Our research article titled “Polymerization/Depolymerization-Induced Self-Assembly under Coupled Equilibria of Polymerization with Self-Assembly” by Jiyun Nam, Changsu Yoo, and Myungeun Seo was recently published in the Journal of the American Chemical Society.
Biomacromolecules like actin achieve the growth of 1D nanostructures from monomers through a balance between polymerization and depolymerization. In synthetic polymers, the thermodynamics of polymerization are governed by negative enthalpy changes and negative entropy changes. When the temperature exceeds the ceiling temperature (Tc), depolymerization from polymer to monomer occurs. While depolymerization has been studied for chemical recycling, especially for small-sized heterocyclic monomers, its effect on self-assembly behavior remains unknown.
To investigate this, we studied the polymerization thermodynamics of valerolactone in various solvents and the self-assembly behavior of nanoparticles during polymerization/depolymerization-induced self-assembly (PDISA) conditions, where the monomer is soluble in the solvent but their polymer is not. We polymerized valerolactone from the polyethylene glycol monomethyl ether as a macroinitiator in different qualities of solvents to establish thermodynamic parameters. The depression of Tc was observed when the incompatibility between the growing block and the solvent was high. The depression originated from the additional entropic loss upon spontaneous micellization of polymers to minimize contact between the growing block and the selective solvent.
We also investigated the morphology transitions during PDISA cycles. The nanoparticles of fiber morphology at room temperature underwent depolymerization at elevated temperatures, resulting in a change in the packing parameter and a transition to rod morphology. The fiber morphology recovered when the temperature was lowered back to room temperature.
Lastly, the viscosity of the polymerization mixture could be manipulated upon consecutive polymerization and depolymerization. The viscosity decreased at higher temperatures and increased again by lowering the temperature. This method may be useful for reversible viscosity control by taking advantage of viscosity change in solution depending on the shape and contents of nanoparticles.
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