AbstractOptically active poly((S)‐isopropylethylene oxide) (poly(5)) was prepared and its specific rotation, [α] D25, was found to be −39,1 and −10,0 in cyclohexane and in benzene, respectively. The NMR spectra of poly(5) were measured in deuterated cyclohexane, in deuterated benzene and in deuterated chloroform at various temperatures. From the coupling constants, the conformer populations about the CC bond of the main chain were calculated to be T = 29%, G+= 50% and G−= 21%.From the optical rotation and NMR behaviours, combined with the results of conformational analysis, the interaction between the solvent benzene and the main chain of poly(isopropylethylene oxide) was concluded to be much weaker than that of poly(propylene oxide). This difference in solvent interaction may be the cause of different ORD behaviours of these two poly(alkylene oxide)s in cyclohexane and in benze