Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Summary

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Abstract

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (λ = 460 nm, 0.7 mW/cm²), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)₃Cl₂ can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

Introduction

The synthesis of nonspherical (and other) nanoparticle morphologies has traditionally been accomplished using a multistep self-assembly procedure starting with the synthesis and purification of well-defined amphiphilic diblock (or multiblock) copolymers. One of the most common self-assembly techniques was popularized by Eisenberg in the 1990s and involves the dissolution of the amphiphilic block copolymer in a common solvent for both polymer blocks followed by the slow addition of a solvent selective for one of the blocks^1-3. As the selective solvent (typically water) is added, the block copolymer undergoes self-assembly to form polymeric nanoparticles. The....

Protocol

1. Synthesis and Characterization of POEGMA Macro-CTA

1. Add oligo(ethylene glycol) methyl ether methacrylate (OEGMA) (12 g, 4 × 10^-2 mol), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPADB) (0.224 g, 8 × 10^-4 mol), 2,2′-azobis(2-methylpropionitrile) (AIBN) (16.4 mg, 0.1 mmol) and 50 ml acetonitrile (MeCN) to a 100 ml round bottom flask.
2. Seal the flask with an appropriately sized rubber septum and steel wire and cool the flask from room temperature to < 4 °C in an ice-water bath.
3. Deoxygenate the flask for 30 min by bubbling nitrogen directly into the reaction mixture through a 21 G need....

Results

In this study, two-step polymerization protocol is used for the synthesis of worm-like micelles using a PISA approach (Figure 1). In the first step, the polymerization of OEGMA is performed yielding a POEGMA macro-CTA which can be used as a stabilizer in the subsequent polymerization step. The PET-RAFT polymerization proceeds under dispersion conditions owing to the insolubility of PBzMA in ethanol which ultimately leads to nanoparticle formation. During the polymerizatio.......

Discussion

This visualized protocol demonstrates the ability to monitor the formation of worm-like micelles simply by observing the onset of gel-like behavior. The utility of this approach lies in the ability to monitor worm formation during the polymerization in comparison to other methods. This procedure can be performed using a two-step polymerization of two commercially available monomers (OEGMA and BzMA) to yield self-assembled POEGMA-b-PBzMA amphiphilic diblock copolymers.

It should be not.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
4-Cyano-4- (phenylcarbonothioylthio)pentanoic acid (CPADB)	Sigma-Aldrich	722995-5G
Oligo(ethylene glycol) methyl ether methacrylate (OEGMA)	Sigma-Aldrich	447935-500ML	Average Mn 300, contains 100 ppm MEHQ as inhibitor, 300 ppm BHT as inhibitor
2,2′-Azobis(2-methylpropionitrile) (AIBN)	Sigma-Aldrich
Ru(bpy)3Cl2.6H2O	Sigma-Aldrich	544981-1G
Benzyl methacrylate (BzMA)	Sigma-Aldrich	409448-1L	Contains monomethyl ether hydroquinone as inhibitor
Aluminium oxide (basic)	Chem-Supply Pty Ltd Australia	AL08371000
95% Ethanol (EtOH)	Sucrogen Bio Ethanol	80889
Acetonitrile (MeCN)	Chem-Supply Pty Ltd Australia	RP1005-G2.5L
Tetrahydrofuran (THF)	Chem-Supply Pty Ltd Australia	TA011-2.5L
Petroleum Spirits (40-60 °C)	Chem-Supply Pty Ltd Australia	PA044-2.5L
Diethyl Ether	Chem-Supply Pty Ltd Australia	EA0362.5L
Dimethylacetamide (DMAc)	VWR International Australia	ALFA22916.M1	For GPC analysis
Pasteur pipettes (230 mm)	Labtek	355.050.503
Glass beakers	Labtek	025.01.902 (2L)/ 2110654 (1L)	2 L beaker is for attaching LED strips to form the circular reactor
Commercial LED strip	EcoLab	n/a	λ = 460 nm, 4.8 W/m
4 ml Glass Vials	Labtek	APC502214B
0.9 ml Quartz Cuvette	Starna Scientific Ltd	21/Q/2
Needle (0.8 mm x 38 mm)	Beckton Dickson	302017	For deoxygenating reactions
Needle (0.8 mm x 120 mm)	B Braun Australia	4665643	For deoxygenating reactions
Sleeve stopper septa (rubber septum)	Sigma-Aldrich	z564680/z564702
Stirring hotplates	VWR International Australia/In Vitro Technologies	97018-488/RADRR91200
Vortex mixer	VWR International Australia	412-0098
Vacuum oven	In Vitro Technologies	MEMVO200