Thermoreversible crystallization-driven aggregation of diblock copolymer nanoparticles in mineral oil.

Matthew J Derry,Steven P Armes,Oleksandr O Mykhaylyk,Anthony J Ryan

doi:10.1039/c8sc00762d

Matthew J Derry, Steven P Armes + Show 2 more

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https://doi.org/10.1039/c8sc00762d

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Abstract

A poly(behenyl methacrylate)37 (PBeMA37) macromolecular chain transfer agent is utilized for the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) directly in mineral oil at 90 °C. Polymerization-induced self-assembly (PISA) occurs under these conditions, yielding a series of sterically-stabilized PBeMA37-PBzMA x diblock copolymer spheres of tunable diameter as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies. Rheological studies indicate that a relatively transparent, free-flowing, concentrated dispersion of non-interacting 32 nm PBeMA37-PBzMA100 spheres at 50 °C forms a turbid, paste-like dispersion on cooling to 20 °C. Turbidimetry and differential scanning calorimetry (DSC) studies conducted on solutions of PBeMA37 homopolymer in mineral oil suggest that this switchable colloidal stability is linked to crystallization-induced phase separation exhibited by this stabilizer block. Indeed, variable-temperature small-angle X-ray scattering (SAXS) indicates that a loose mass fractal network of strongly interacting spheres is formed on cooling to 20 °C, which accounts for this thermoreversible sol-gel transition. Moreover, SAXS, DSC and wide-angle X-ray scattering (WAXS) analyses indicate that the behenyl (C22H45) side-chains first form crystalline domains comprising adjacent stabilizer chains within individual spherical nanoparticles, with subsequent crystallization between neighboring nanoparticles leading to the formation of the mass fractal aggregates.

Highlights

Over the past 20 years or so, there has been considerable and growing interest in crystallization-driven block copolymer selfassembly (CDSA)
Oscillatory rheology experiments performed on the same 20% w/w dispersion of 32 nm poly(behenyl methacrylate)37 (PBeMA37)–PBzMA100 spheres in mineral oil are consistent with the transition temperatures determined by differential scanning calorimetry (DSC)
A series of PBeMA37–PBzMAx spherical nanoparticles are prepared via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate at 90 C in mineral oil at 20% w/w solids

Summary

Introduction

Over the past 20 years or so, there has been considerable and growing interest in crystallization-driven block copolymer selfassembly (CDSA). The near-monodisperse PBeMA37 macro-CTA (Mw/Mn 1⁄4 1.18) obtained from the RAFT solution polymerization of BeMA in toluene at 70 C was utilized for the RAFT dispersion polymerization of BzMA in mineral oil at 90 C to produce a range of PBeMA37–PBzMAx diblock copolymer spheres (see Table 1).

Results

Conclusion