Block copolymer microparticles comprising inverse bicontinuous phases prepared via polymerization-induced self-assembly.

Pengcheng Yang,Thomas J Neal,Steven P Armes,Bryony R Parker,Yin Ning,Elizabeth R Jones

doi:10.1039/c9sc00303g

Pengcheng Yang, Thomas J Neal + Show 4 more

Open Access

https://doi.org/10.1039/c9sc00303g

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Abstract

Traditionally, post-polymerization processing routes have been used to obtain a wide range of block copolymer morphologies. However, this self-assembly approach is normally performed at rather low copolymer concentration, which precludes many potential applications. Herein, we report a facile method for the preparation of block copolymer particles exhibiting complex internal morphology via polymerization-induced self-assembly (PISA). More specifically, a series of diblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) alternating copolymerization of styrene (St) with N-phenylmaleimide (NMI) using a poly(N,N-dimethylacrylamide) (PDMAC) stabilizer as a soluble precursor. Conducting such PISA syntheses in a 50 : 50 w/w ethanol/methyl ethyl ketone (MEK) mixture leads directly to the formation of micrometer-sized PDMAC-P(St-alt-NMI) diblock copolymer particles at 20% w/w solids. Adjusting the degree of polymerization (DP) of the core-forming P(St-alt-NMI) block to target highly asymmetric copolymer compositions provides convenient access to an inverse bicontinuous phase. TEM studies of intermediate structures provide useful insights regarding the mechanism of formation of this phase. SEM studies indicate that the final copolymer particles comprise perforated surface layers and possess nanostructured interiors. In addition, control experiments using 1,4-dioxane suggest that the high chain mobility conferred by the MEK co-solvent is essential for the formation of such inverse bicontinuous structures. One-pot PISA formulations are reproducible and involve only cheap, commercially available starting materials, so they should be readily amenable to scale-up. This augurs well for the potential use of such nanostructured micrometer-sized particles as new organic opacifiers for paints and coatings.

Highlights

It is well-known that AB diblock copolymers undergo spontaneous self-assembly to form ordered nanostructures both in the bulk[1] and in solution.[2]
Control experiments using 1,4-dioxane suggest that the high chain mobility conferred by the methyl ethyl ketone (MEK) co-solvent is essential for the formation of such inverse bicontinuous structures
The observation of trapped intermediates during the oligolamellar vesicles (OLV) to perforated ellipsoidal lamellae (PEL) to BE transitions suggest that the mechanism for formation of these latter morphologies involves three steps: (i) initial OLV phase separation, which results in the formation of worm-like particles and hollow bilayer structures; (ii) fusion/ stacking of hollow bilayers to generate large aggregates – both TEM and SEM studies indicate a signi cant increase in particle size during the OLV to PEL transition; (iii) rearrangement to form more ordered

Summary

Introduction

It is well-known that AB diblock copolymers undergo spontaneous self-assembly to form ordered nanostructures both in the bulk[1] and in solution.[2]. We reported the preparation of conventional diblock copolymer nanoparticles via RAFT dispersion alternating copolymerization of styrene (St) with N-phenylmaleimide (NMI) utilizing a 50 : 50 w/w ethanol/MEK mixture and a non-ionic poly(N,N0-dimethylacrylamide) (PDMAC) stabilizer.[51] The resulting P(St-alt-NMI) core-forming block has a relatively high Tg (219 C),[52] which leads to the formation of oligolamellar vesicles (OLV) during PISA, as well as the more typical sphere and worm phases.

Results

Conclusion