端基间多重氢键对聚乳酸结晶行为的影响及响应OA

To clarify the effect of terminal hydrogen bonding on the crystallization behavior and dynamic response mechanism of polymers,single-ended 2-ureido-4[1H]-pyrimidinone(UPy)functionalized polylactide(UPLLA)with different molecular weights(5,9,12 kg/mol)were synthesized and investigated.¹H NMR and Fourier transform infrared spectroscopy(FTIR)confirmed the successful incorporation of UPy groups onto the PLA chain ends.Differential scanning calorimetry analysis revealed that terminal hydrogen bonding significantly suppressed the melt crystallization ability of PLA,resulting in elevated cold crystallization temperatures(increasing from 84.7℃to 99.6℃for the 5k sample),reduced cold crystallization enthalpies(decreasing from 43.1 J/g to 15.4 J/g for the 5k sample)and melting enthalpies(decreasing from 30.6 J/g to 8.1 J/g for the 5k sample),and depressed melting temperatures(a decrease of 17.9℃for the 5k sample).The suppressive effect weakened with increasing molecular weight,primarily attributed to the attenuation of the dragging effect of terminal groups on molecular chain motion as chain length increased.In situ variable-temperature FTIR studies further elucidated the dynamic response mechanism of terminal hydrogen bonding.During the recrystallization-melting process,the enhanced molecular chain mobility released upon melting of the α'-crystals drove the reorganization of terminal hydrogen bonds,leading to an anomalous increase in hydrogen bonding strength within the 100～130℃temperature range for the 9k and 12k samples,thereby confirming that terminal hydrogen bonds could respond to polymer phase transitions.