Preparation, characterization, and dilute solution properties of four‐branched cage‐shaped poly(ethylene oxide)

Abstract

AbstractA four‐branched cage‐shaped poly(ethylene oxide) (4C‐PEO) was prepared by a coupling reaction at very dilute condition between two kinds of end‐functional four‐armed star‐shaped PEOs having amino and N‐hydroxysuccinimide groups on their four ends, followed by purification using α‐cyclodextrin (α‐CD). The raw coupling reaction product shows multiple peaks including various high molecular weight multimeric products in size‐exclusion chromatography measurements, while the product after α‐CD purification shows a single peak eluted slightly earlier than the precursor star PEOs. Moreover, the final product obtained has about twice higher molecular weight than the star precursors. These results suggest that the targeted 4C‐PEO polymer was successfully isolated through the α‐CD purification. Small‐angle neutron scattering (SANS) measurements of the final product in dilute solution were conducted, and its chain conformation was evaluated from the scattering profile in comparison with linear and star polymers. It has been found that the cage‐shaped sample exhibits a distinct peak at lower q‐region in the Kratky plot, which is in strong contrast with the linear counterpart. This result must be originated from the characteristic cage‐shaped architecture, that is, having branched and closed‐loop configurations, and hence having higher segmental density than simple linear and star molecules. In fact, the present experimental result is consistent with the recent Monte Carlo simulation reported by Uehara and Deguchi.