Inter-end-group hydrogen bonding modulates crystallization and polymorphic transition of poly(butylene adipate)

Telechelic poly(butylene adipate) (PBA) bearing terminal 2-ureido-4[1H]-pyrimidinone (UPy) moieties was synthesized to investigate hydrogen bond-mediated melt crystallization and crystal transition behavior. Differential scanning calorimetry and wide-angle X-ray diffraction revealed that quadruple hydrogen-bonding interactions among UPy moieties significantly suppressed the overall crystallinity and altered polymorphic selectivity. Compared to hydroxyl-terminated PBA (HPBA), UPy-terminated PBA (UPBA) exhibited an expanded temperature window for forming the thermodynamically stable α-crystal and a broader α/β crystals coexistence region during isothermal crystallization, indicating retarded β-crystal growth kinetic advantage. UPy end groups enhanced the melt memory effect by stabilizing mesomorphic structure, widening the self-nucleation domain (Domain IIa). In situ temperature-resolved Fourier transform infrared spectroscopy investigation demonstrated that the hydrogen-bonding interactions among terminal UPy moieties are sensitive to the melting and crystallization process of PBA. Critically, the slow increase in UPy hydrogen-bonding intensity coinciding with β-crystal melting, followed by a sharp decrease during α-crystal formation, provided direct evidence that the β to α crystal transition in UPBA predominantly follows a melt-recrystallization mechanism rather than a solid-solid transformation.