Effect of Molecular Architecture on Associating Behavior of Star-Like Amphiphilic Polymers Consisting of Plural Poly(ethylene oxide) and One Alkyl Chain

Associating behavior of star-like amphiphilic polymers consisting of two or three poly(ethylene oxide) (PEO) chains and one stearyl chain (C18) was investigated. Although the aggregation number (N-agg) of linear analogue of amphiphilic polymers monotonically decreased with increasing number-average molecular weight of PEO (M-n(,PEO)), the N-agg of micelles of star-like amphiphilic polymers with M-n(,PEO) = 550 g/mol was smaller than that with M-n(,PEO) = 750 g/mol, whereas that with M-n(,PEO) >= 750 g/mol showed general M-n(,PEO) dependence. Small-angle X-ray scattering analyses revealed that the occupied area of one PEO chain on the interface between hydrophobic core and corona layer in the micelles of star-like polymers was much narrower than that in the linear amphiphilic polymers. This result indica ted the PEO chains of star-like polymers partially took unfavorable conformation near the core-corona interface in polymer micelles. The effect of local conformation of PEO chains near the interface on the associating behavior became significant as M-n(,PEO) decreased. Therefore, in polymer micelles of star-like amphiphilic polymers containing PEO with M-n(,PEO) = 550 g/mol, the enlargement of occupied area of PEO on the core-corona interface should be caused to avoid the formation of unfavorable conformations of partial PEO chains, resulting in a decrease in N(agg)s.

Automated summary

The conformation of PEO chains in star-like amphiphilic polymers has a significant impact on their associating behavior, especially when the number-average molecular weight of PEO is low. Adjusting the occupied area of PEO chains on the core-corona interface is necessary to avoid unfavorable conformations, which can lead to a decrease in aggregation numbers.