RAFT Dispersion Alternating Copolymerization of Styrene with N-Phenylmaleimide: Morphology Control and Application as an Aqueous Foam Stabilizer.

Pengcheng Yang,Oleksandr O Mykhaylyk,Steven P Armes,Elizabeth R Jones

doi:10.1021/acs.macromol.6b01563

Pengcheng Yang, Oleksandr O Mykhaylyk + Show 2 more

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https://doi.org/10.1021/acs.macromol.6b01563

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Journal: Macromolecules	Publication Date: Sep 2, 2016
Citations: 42	License type: cc-by

Affiliation: University of Sheffield

Abstract

We report a new nonaqueous polymerization-induced self-assembly (PISA) formulation based on the reversible addition–fragmentation chain transfer (RAFT) dispersion alternating copolymerization of styrene with N-phenylmaleimide using a nonionic poly(N,N-dimethylacrylamide) stabilizer in a 50/50 w/w ethanol/methyl ethyl ketone (MEK) mixture. The MEK cosolvent is significantly less toxic than the 1,4-dioxane cosolvent reported previously [YangP.; Macromolecules2013, 46, 8545−8556]. The core-forming alternating copolymer block has a relatively high glass transition temperature (Tg), which leads to vesicular morphologies being observed during PISA, as well as the more typical sphere and worm phases. Each of these copolymer morphologies has been characterized by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. TEM studies reveal micrometer-sized elliptical particles with internal structure, with SAXS analysis suggesting an oligolamellar vesicle morphology. This structure differs from that previously reported for a closely related PISA formulation utilizing a poly(methacrylic acid) stabilizer block for which unilamellar platelet-like particles are observed by TEM and SAXS. This suggests that interlamellar interactions are governed by the nature of the steric stabilizer layer. Moreover, using the MEK cosolvent also enables access to a unilamellar vesicular morphology, despite the high Tg of the alternating copolymer core-forming block. This was achieved by simply conducting the PISA synthesis at a higher temperature for a longer reaction time (80 °C for 24 h). Presumably, MEK solvates the core-forming block more than the previously utilized 1,4-dioxane cosolvent, which leads to greater chain mobility. Finally, preliminary experiments indicate that the worms are much more efficient stabilizers for aqueous foams than either the spheres or the oligolamellar elliptical vesicles.

Highlights

Over the past 5 years or so, polymerization-induced selfassembly (PISA) has become widely recognized as an efficient and versatile route to prepare block copolymer nanoobjects.[1−26] In principle, PISA can be performed using any type of living polymerization chemistry, but in practice the majority of PISA literature examples are based on reversible addition−fragmentation chain transfer (RAFT) polymerization.[27−29] In PISA a soluble polymer A is chainextended with a second polymer B that is insoluble in the solvent selected for the polymerization
A new PISA formulation based on the RAFT dispersion alternating copolymerization of styrene with N-phenylmaleimide is reported that utilizes a 50/50 w/w ethanol/ methyl ethyl ketone (MEK) mixture and a nonionic poly(N,N-dimethylacrylamide) stabilizer
transmission electron microscopy (TEM) studies indicate the formation of micrometer-sized oligolamellar elliptical vesicles, with small-angle X-ray scattering (SAXS) analysis suggesting a mean degree of lamellae stacking of 2−3 layers

Summary

■ INTRODUCTION

Over the past 5 years or so, polymerization-induced selfassembly (PISA) has become widely recognized as an efficient and versatile route to prepare block copolymer nanoobjects.[1−26] In principle, PISA can be performed using any type of living polymerization chemistry, but in practice the majority of PISA literature examples are based on RAFT polymerization.[27−29] In PISA a soluble polymer A is chainextended with a second polymer B that is insoluble in the solvent selected for the polymerization. Some block copolymer chains are generated earlier than others, yielding a somewhat broader molecular weight distribution than that normally expected for a RAFT synthesis.[43] In related work, Charleux et al reported relatively slow consumption of RAFT agent during chain extension of a PDMAC macro-CTA with n-butyl acrylate using a RAFT aqueous emulsion polymerization formulation.[44] Such observations are quite typical for many PISA syntheses[12−14,33] but are in marked contrast to our observations during the PISA synthesis of PMAA-P(St-alt-NMI) diblock copolymer nanoparticles in a 50/50 w/w ethanol/1,4-dioxane mixture.[35] In this earlier study, a slightly retarded rate of polymerization was observed after micellar nucleation. The relatively rigid nature of the individual worms most likely leads to greater mechanical integrity of the adsorbed worm layer, which further enhances the foam stability.[55]

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES