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

Daisuke Kugimoto,Masaki Kinoshita,Isamu Akiba,Aoi Taniguchi

doi:10.3390/polym13030460

Abstract

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 (Nagg) of linear analogue of amphiphilic polymers monotonically decreased with increasing number-average molecular weight of PEO (Mn,PEO), the Nagg of micelles of star-like amphiphilic polymers with Mn,PEO = 550 g/mol was smaller than that with Mn,PEO = 750 g/mol, whereas that with Mn,PEO ≥ 750 g/mol showed general Mn,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 Mn,PEO decreased. Therefore, in polymer micelles of star-like amphiphilic polymers containing PEO with Mn,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 Naggs.

Highlights

Amphiphilic polymers, such as block copolymers composed of hydrophobic and hydrophilic polymer chains and hydrophobically modified water-soluble polymers, spontaneously assemble into polymer micelles consisting of a hydrophobic core and hydrated corona in aqueous solution [1]
It is considered that the unique associating behavior in the star-like amphiphilic polymers having multiple hydrophilic poly(ethylene oxide) (PEO) chains should remarkably appear in the region where the chain length of PEO is relatively short
SAXS measurements revealed that the occupied area of one PEO chain on the interface between hydrophobic core and corona in (PEOx)2-C18 and (PEOx)3-C18 micelles were much narrower than that in (PEOx)1-C18 micelles

Summary

Introduction

Amphiphilic polymers, such as block copolymers composed of hydrophobic and hydrophilic polymer chains and hydrophobically modified water-soluble polymers, spontaneously assemble into polymer micelles consisting of a hydrophobic core and hydrated corona in aqueous solution [1]. Because polymer micelles have a suitable size in the range of several nm to several 100 nm, accumulate in tumors, can uptake hydrophobic compounds as anticancer drugs, and show a “stealth effect” which is a function that is not captured by a reticuloendothelial system such as a liver, they are attracting much attention in drug delivery systems as drug vehicles [2,3,4,5,6] Such polymer micelles can have various shapes, sizes and radial density distributions depending on the length of hydrophobic and hydrophilic polymer chains, hydrophobicity, excluded volume interactions between the hydrophilic polymer chains in swollen corona and so on [7,8,9]. In this study, we focus on the effects on the number and chain length of hydrophilic chains on the associating behavior of star-like amphiphilic polymers consisting of one hydrophobic alkyl chain and plural poly(ethylene oxide) (PEO) as a hydrophilic chain

Methods

Results

Conclusion