Issue 24, 2015

From multi-responsive tri- and diblock copolymers to diblock-copolymer-decorated gold nanoparticles: the effect of architecture on micellization behaviors in aqueous solutions

Abstract

This work reports on the aqueous stimuli-responsive behaviors of an ABA triblock copolymer, a BAB triblock copolymer, an AB diblock copolymer and citrate-based gold nanoparticles decorated with AB diblock copolymers (where A is the pH- and thermo-responsive poly[N,N-(dimethylamino)ethyl methacrylate] (PDMAEMA) and B is the thermo-responsive poly[2-(2-methoxyethoxy)ethyl methacrylate] (PMEO2MA)). The symmetric triblock polymers were synthesized via sequential atom transfer radical polymerization (ATRP) using a disulfide-functionalized initiator. Subsequently, the thiol-ended diblock copolymers were facilely obtained by reducing these triblock copolymers and were grafted onto gold nanoparticle (AuNP) surfaces via ligand exchange to yield stimuli-sensitive gold nanoparticles (Au@AB and Au@BA). The ABA and BAB triblock copolymers exhibited two-step thermo-induced aggregation behavior in water at a pH near the isoelectric point (IEP), which resulted in the formation of micelles after the first lower critical solution temperature (LCST) and large aggregates consisting of clustered micelles above the second LCST transition. The significant difference between the micelle sizes of the ABA and BAB copolymers, such that the micelle size of the BAB copolymer was smaller than that of the ABA copolymer although both had a similar unit composition, suggests a distinction between the micelle structures. The “branch” and “flower-like” micelles that are formed in the ABA and BAB aqueous solutions, respectively, ultimately governed the phase transition behaviors. The AB diblock copolymer exhibited similar micellization behavior and a micelle size roughly similar to that of the ABA triblock copolymer, although the chain length of the AB copolymer is only half that of the ABA copolymer. Both Au@PDMAEMA–PMEO2MA and Au@PMEO2MA–PDMAEMA showed similar dual LCST behaviors and pH-responsive behaviors in aqueous solutions without the addition of salt. A significant difference was observed between the two types of hybrid AuNPs in salty solutions, in which only the Au@PDMAEMA–PMEO2MA system exhibited thermo-induced aggregation behavior. These hybrid nanoparticles can be used as phase transfer reagents. Additionally, AuNPs capped with PDMAEMA–PMEO2MA diblock copolymer can spontaneously transfer across a water–toluene interface.

Graphical abstract: From multi-responsive tri- and diblock copolymers to diblock-copolymer-decorated gold nanoparticles: the effect of architecture on micellization behaviors in aqueous solutions

Supplementary files

Article information

Article type
Paper
Submitted
12 Apr 2015
Accepted
11 May 2015
First published
12 May 2015

Soft Matter, 2015,11, 4830-4839

Author version available

From multi-responsive tri- and diblock copolymers to diblock-copolymer-decorated gold nanoparticles: the effect of architecture on micellization behaviors in aqueous solutions

L. Song, H. Sun, X. Chen, X. Han and H. Liu, Soft Matter, 2015, 11, 4830 DOI: 10.1039/C5SM00859J

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