Synthesis and Characterization of Polyurethanes Crosslinked by Polyrotaxanes of Two Filling Ratios of α-Cyclodextrin and with Two Modification Ratios of Polyurethane Chain

Four polyurethanes (PUs) crosslinked by polyrotaxanes (PRXs) of two filling ratios of CyD (63% for PRX4000 and 37% for PRX6000) and with modification ratios of 1 and 2 for a PU chain. The PUs were abbreviated as PU6000(1) , PU6000(2) , PU4000(1) , and PU4000(2) , in which 4000 and 6000 are the molecular weights of PEGs as an axle molecule of the PRX and the numbers in parentheses are the modification ratios of the PU chain. ATR-FT-IR, DSC, viscoelastic measurements and tensile test were carried out to investigate their thermal and physical properties. The formation of hydrogen bonds between the PU chains increased with increase in the modification ratio of the PU chain. PU4000(2) possessing the half filling ratio of CyD and higher modification ratio of the PU chain made the recrystal lization of the soft segment slow. PU4000(1) with the half filling ratio of CyD and lower modification ratio of the PU chain showed the highest tensile strength among the PUs. In contrast, PU6000(2) with the lower filling ratio of CyD and higher modification ratio of the PU chain showed the highest elongation among the PUs, implying that the sliding effect based on the rotaxane structure occurred.