Structural control in micelles of alkyl acrylate-acrylate copolymers via alkyl chain length and block length

Özge Azeri,Michael Gradzielski,Dennis Schönfeld,Laurence Noirez

doi:10.1007/s00396-020-04663-y

Abstract

Amphiphilic copolymers with poly (alkyl acrylate) as hydrophobic and poly (acrylic acid) (AA) as hydrophilic block have been synthesised. The alkyl chain was varied from butyl to dodecyl, thereby varying systematically the polarity of the hydrophobic block whose length was between 35 and 70, while the PAA block had ~ 100 units. Such relatively short amphiphiles should equilibrate quickly in aqueous solution, and their corresponding self-assembly properties were characterised by means of critical micelle concentration (cmc) determination. Detailed information regarding the aggregate structures was obtained by static light scattering (SLS) and small angle neutron scattering (SANS). This could be correlated with the molecular architecture of the copolymers and the degree of ionisation of the PAA block. Generally, it is found that the aggregation numbers become smaller upon fully charging the PAA head group and only for dodecyl acrylate really well-defined micellar aggregates are formed. This means that the extent of hydrophobicity of the alkyl acrylate block and its length determine in a clear fashion the propensity for micelle formation and the mass and aggregation number of the formed micelles.Graphical abstract

Highlights

Amphiphilic block copolymers with a hydrophilic and a hydrophobic block are able to form micelles in aqueous solution and such systems have been studied to quite some extent due to the fact that there is an enormous richness in terms of combining different hydrophilic and hydrophobic copolymer blocks [1], for instance the hydrophilic block can be a polyelectrolyte [2, 3] or a nonionic water soluble polymer, like polyethylene oxide [4,5,6]
Pyrene has to be located within an aqueous environment, while above it with large preference be contained in the hydrophobic core of the block copolymer micelles
The self-assembly of these amphiphilic block copolymers was studied in aqueous solution, where the degree of ionisation of the polyacrylic acid (PAA) block was varied from 20 to 100%

Summary

Introduction

Amphiphilic block copolymers with a hydrophilic and a hydrophobic block are able to form micelles in aqueous solution and such systems have been studied to quite some extent due to the fact that there is an enormous richness in terms of combining different hydrophilic and hydrophobic copolymer blocks [1], for instance the hydrophilic block can be a polyelectrolyte [2, 3] or a nonionic water soluble polymer, like polyethylene oxide [4,5,6] Such block copolymer micelles are interesting for a number of applications, such as drug delivery [7], in nanomedicine [8], or nanolithography [9]. Quite frequently, such micelles are stimuli-responsive, for instance if the hydrophilic head group is a polycarboxylate or a polyamine which are switchable with respect to their charge by pH changes in the range of pH 5–9 [15, 16]. Such responsiveness together with the ability to incorporate payloads of drugs makes block copolymer micelles attractive as tunable delivery vehicles for nanomedicine applications, as reviewed recently [8, 19]

Methods

Results

Conclusion