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Updated: Nov 9, 2025

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers
Published on: December 16, 2022
Entropy-Driven Supramolecular Ring-Opening Polymerization of a Cyclic Hemoglobin Monomer for Constructing a
Takashi Matsuhira1, Hiromi Sakai1
1Department of Chemistry, Nara Medical University, 840 Shijo-cho, Kashihara 634-8521, Japan.
Abstract:
Our earlier report described that a cyclic hemoglobin (Hb) monomer with two β subunits of a Hb molecule (α2β2) bound through a flexible polyethylene glycol (PEG) chain undergoes reversible supramolecular ring-opening polymerization (S-ROP) to produce a supramolecular Hb polymer with a Hb-PEG alternating structure. In this work, we polymerized cyclic Hb monomers with different ring sizes (2, 5, 10, or 20 kDa PEG) to evaluate the thermodynamics of S-ROP equilibrium. Quantification of the produced supramolecular Hb polymers and the remaining cyclic Hb monomers in the equilibrium state revealed a negligibly small enthalpy change in S-ROP (ΔHp ≤ 1 kJ·mol-1) and a markedly positive entropy change increasing with the ring size (ΔSp = 26.8-33.2 J·mol-1·K-1). The results suggest an entropy-driven mechanism in S-ROP: a cyclic Hb monomer with the larger ring size prefers to form a supramolecular Hb polymer. The S-ROP used for this study has the potential to construct submicrometer-sized Hb-PEG alternating polymers having structural regularity.
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