Weak Hydrogen Bonding in Biodegradable Polymers

Intermolecular ═C–H···O═C Hydrogen Bonding and Conformational Preference in Crystalline Poly(butylene 2,5-furandicarboxylate)

“…On the contrary, the nearer distance between the carbonyl O 2 and the two H atoms of furan in the adjacent chain, i.e., O 2 ···H 2 (④4.11 Å), is much longer than 2.72 Å. In addition, the closest interatomic distance between the carbonyl O 2 and H atoms of opposite BG group, i.e., O 2 ···H 3 (⑤2.71 Å), is almost equal to the van der Waals separation, ruling out the presence of the weak hydrogen bonding between the CO and CH 2 groups, which has been widely reported to happen in the crystalline structures of biodegradable polymers . Finally, the possible intermolecular interactions between the cyclic ether oxygen and furan-ring hydrogen atoms can also be excluded by the shortest interatomic distance of O 3 ···H 2 (③2.93 Å) again exceeding the van der Waals separation of 2.72 Å.…”

“…••H 3 (⑤2.71 Å), is almost equal to the van der Waals separation, ruling out the presence of the weak hydrogen bonding between the C�O and CH 2 groups, which has been widely reported to happen in the crystalline structures of biodegradable polymers. 41 Finally, the possible intermolecular interactions between the cyclic ether oxygen and furan-ring hydrogen atoms can also be excluded by the shortest interatomic distance of O 3 •••H 2 (③2.93 Å) again exceeding the van der Waals separation of 2.72 Å. The calculations indicate that in the crystalline state of PBF there should be an attractive intermolecular �C−H•••O�C interaction between the carbonyl C�O 1 and the two furan-ring �C−H groups of adjacent chains, even though the C�O 2 group is free of attraction.…”

“…hydrogen bonding, respectively. 41 In the following, to approval the existence of �C−H•••O�C hydrogen bonding in the crystalline state of PBF and then to unveil its underlying nature, structural evolution of semicrystalline PBF during the heating process at 10 °C/min from 30 to 200 °C is real time followed by means of variable temperature FTIR and WAXD techniques.…”

“…59 This point indicates that such an intermolecular �C−H•••O�C attractive interaction in the crystalline state of PBF should be the true hydrogen bonding rather than the weak C−H•••O contact in commonly biodegradable polyesters. 41 To further elucidate this essence, its thermostability upon heating is investigated.…”

“…bands in IR relative to those of the amorphous state. 28−32 Recently, Sato has summarized such an C−H•••O interaction as the weak hydrogen bonding in biodegradable polymers, 41 unlike the truly strong hydrogen bonding in X−H (X = O, N, etc.) systems such as the N−H••• O�C hydrogen bonds in polyamides.…”