To investigate the effect of the macromonomeric length of ureidopyrimidinone-based supramolecular polymers on their crystalline structure and mechanical/rheological properties, we synthesized ureidopyrimidinone-end functional poly(tetramethylene glycol), U(PTMG), with varied molecular weight (1k, 2k, and 3k g·mol−1). From 1H NMR, FT-IR, and specific viscosity analysis, we confirmed chain extension of U(PTMG)s by the quadruple hydrogen bonding of ureidopyrimidinone, indicating successful formation of U(PTMG) supramolecular polymers. We found that the U(PTMG) supramolecular polymers had dual-crystalline structures composed of PTMG and UPy crystals. The rigid UPy crystals, which had relatively high melting temperatures, were dominant with decreasing macromonomeric lengths of the U(PTMG) supramolecular polymers, whereas the chain-folded PTMG crystals were drastically reduced. As a result, the mechanical and rheological properties of the U(PTMG) supramolecular polymers became rigid and elastic, with decreasing macromonomer lengths of the U(PTMG) supramolecular polymers, due to their increased portions of UPy crystals.
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