Small-Angle X-Ray Scattering Studies of Block Copolymer Nano-Objects: Formation of Ordered Phases in Concentrated Solution During Polymerization-Induced Self-Assembly.

Matthew J Rymaruk,Csilla György,Bastien Darmau,Steven P Armes,Cate T O'Brien,Oleksandr O Mykhaylyk,James Jennings

doi:10.1002/anie.202101851

Matthew J Rymaruk, Csilla György + Show 5 more

Open Access

https://doi.org/10.1002/anie.202101851

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Abstract

We report that polymerization‐induced self‐assembly (PISA) can be used to prepare lyotropic phases comprising diblock copolymer nano‐objects in non‐polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 °C using a trithiocarbonate‐capped hydrogenated polybutadiene (PhBD) steric stabilizer block in n‐dodecane produces either spheres or worms that exhibit long‐range order at 40 % w/w solids. NMR studies enable calculation of instantaneous copolymer compositions for each phase during the BzMA polymerization. As the PBzMA chains grow longer when targeting PhBD80–PBzMA40, time‐resolved small‐angle X‐ray scattering reveals intermediate body‐centered cubic (BCC) and hexagonally close‐packed (HCP) sphere phases prior to formation of a final hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms. The HEX phase undergoes an order–disorder transition on heating to 150 °C and a pure HCP phase forms on cooling to 20 °C.

Highlights

It is widely recognized that polymerization-induced selfassembly (PISA) is a powerful and versatile platform technology for the rational design of various types of block copolymer nano-objects.[1,2,3,4] polymerization-induced self-assembly (PISA) enables the efficient production of such nano-objects in the form of concentrated [+] These authors contributed to this work
Time-resolved small-angle X-ray scattering (SAXS) has been used to monitor the evolution in copolymer morphology that occurs during the PISA synthesis of PhBD80–PBzMA40 diblock copolymer worms at 90 8C in n-dodecane when targeting 40 % w/w solids
As the structure-directing PBzMA block grows during this PISA synthesis, there is a gradual evolution from molecularly dissolved copolymer chains to spheres to closepacked spheres (BCC/hexagonally close-packed (HCP) phases) to a final mixture of hexagonal cylinder phase (HEX) and HCP phases

Summary

Introduction

Angewandte Chemie International Edition published by Wiley-VCH GmbH Zhang et al reported the PISA synthesis of concentrated diblock copolymer worms via the RAFT dispersion polymerization of a cholesterol-based (meth)acrylic monomer in an ethanol/water mixture.[49] Electron microscopy studies indicated that the cholesterol units formed a smectic phase within the worm cores, which stabilized this anisotropic morphology over a relatively wide range of copolymer compositions. Small-angle X-ray scattering (SAXS) provided evidence for the “apparent preferential order” of neighboring worms This was assumed to be a sample preparation artifact rather than a lyotropic phase formed during PISA. We use SAXS to study (i) the in situ evolution in copolymer morphology and intermediate lyotropic phases that occur during PISA, (ii) the serial dilution that eventually leads to a conventional dispersion of worm-like micelles, and (iii) the effect of thermal annealing on these lyotropic phases

Results and Discussion

Conclusion

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