Difference in dilute aqueous solution behavior between poly(ethylene glycol) and poly(ethylene oxide)

Abstract

Static light scattering behavior was examined for poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) of small weight-average molecular weight M w (3 × 103−2 × 104), in methanol and water at 25.0 °C, the former polymer having hydroxy groups at both ends and the latter having a methoxy group at one end and a hydroxy group at the other. It was found that some aggregates of large size are formed in aqueous solutions of the PEO samples with M w = 3.81 × 103 and 7.00 × 103, while all PEG and PEO samples are isolated in methanol solutions, and the PEG samples and the PEO sample of the largest M w (=1.60 × 104) are also isolated even in the aqueous solutions. From the results of dynamic light scattering measurements for the aqueous solution of the PEO sample with M w = 3.81 × 103 at 25.0 °C, there were detected two classes of scatterers having different sizes, i.e., the isolated chains and aggregates, the apparent hydrodynamic radius of the latter being ca. twenty times as large as that of the former. Static light scattering measurements are carried out for poly(ethylene glycol) and poly(ethylene oxide) (PEO) of the weight-average molecular weight M w ranging from 3×103 to 2×104 in methanol and water at 25.0 °C. Some aggregates of large size are found to be formed only in the cases of PEO of M w∼O(103) in aqueous solutions, although for other cases polymer chains are isolated in solutions.