Photoinitiated Polymerization-Induced Self-Assembly via Visible Light

Letter Cite This: ACS Macro Lett. 2019, 8, 205−212

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Photoinitiated Polymerization-Induced Self-Assembly via Visible Light-Induced RAFT-Mediated Emulsion Polymerization Jianbo Tan,*,†,‡ Xiaocong Dai,† Yuxuan Zhang,† Liangliang Yu,† Hao Sun,§ and Li Zhang*,†,‡ †

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Department of Polymeric Materials and Engineering, School of Materials and Energy, Guangdong University of Technology Guangzhou 510006, China ‡ Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter, Guangzhou 510006, China § Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States S Supporting Information *

ABSTRACT: Aqueous emulsion polymerization is one of the most commonly used techniques in industry for the production of polymer latexes. In this contribution, we present photoinitiated polymerization-induced self-assembly (photo-PISA) based on aqueous visible light-induced reversible addition−fragmentation chain transfer (RAFT)-mediated emulsion polymerization at room temperature. A wide range of morphologies including spheres, worms, and vesicles have been achieved at room temperature by modulating reaction parameters. Additionally, this method enables access to inorganic nanoparticles-loaded vesicles by adding inorganic nanoparticles at the beginning of the polymerization. Finally, an oxygen-tolerant RAFT-mediated emulsion polymerization has been developed, allowing the synthesis of polymer nanoobjects at low volumes (e.g., in a 96-well plate). This study is expected to expand the scope of photo-PISA for the preparation of various block copolymer nano-objects in water at room temperature.

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insoluble monomers are employed as the core-forming monomers and hydrophilic macromolecular RAFT (macroRAFT) agents are employed as the stabilizers. Charleux and co-workers,29−31 Davis and co-workers,32 and D’Agosto and co-workers33 reported that higher order morphologies, including worms and vesicles, were accessible by RAFTmediated emulsion polymerization employing statistic copolymers as macro-RAFT agents and styrene as the core-forming (co)monomer. The preparation of higher order morphologies by RAFT-mediated emulsion polymerization of methacrylic or acrylic monomers has rarely been reported. To overcome these limitations, temperature-directed morphology transformation method has been developed using thermoresponsive macroRAFT agents.34,35 Thermal initiation is usually employed to initiate the RAFT-mediated emulsion polymerization at high temperatures (e.g., 70 °C). Upon heating the thermoresponsive macro-RAFT agent above the lower critical solution temperature (LCST), the macro-RAFT agent becomes insoluble and additional surfactant is required to ensure the colloidal stability. It should be noteworthy that the presence of surfactant is not beneficial for applications in many areas (e.g., drug delivery). Moreover, the high reaction temperature hinders the preparation of thermosensitive or biorelated polymer nano-objects. While the method of aqueous RAFTmediated dispersion polymerization has been popular for the

olution self-assembly of amphiphilic block copolymers is a versatile method for the preparation of polymer nanoobjects with a diverse set of morphologies. The obtained polymer nano-objects have broad applications in different areas including catalysis, nanoreactor, biomineralization, drug delivery, and so on.1−4 Typically, the block copolymers are fully solubilized in a good solvent (for both blocks) and then a bad solvent (for one block) is added to drive the self-assembly. However, this cosolvent self-assembly method is typically performed in a diluted solution (solids 98%) was observed in each case when the reaction volume was gradually reduced to 1000, 500, or even 200 μL (Figure 5d). PPEGMA6-PtBA100 diblock copolymer nano-objects prepared at different volumes were then characterized by TEM. Mixed morphologies containing vesicles and worms were obtained in all studied cases (Figure S4), which is consistent with the sample prepared in a 10 mL round-bottom flask (Figure 1f). It should be noteworthy that magnetic stirring is critical for maintaining the colloidal stability during the polymerization. This oxygen-tolerant RAFT-mediated emulsion polymerization provides a promising strategy for nonexperts to prepare polymer nano-objects in a high-throughput manner. In conclusion, a novel photo-PISA method via visible lightinduced RAFT-mediated emulsion polymerization has been established for the synthesis diblock copolymer nano-objects. For the first time, higher order morphologies (including worms, vesicles and vesicles loaded with silica nanoparticles) were prepared by RAFT-mediated emulsion polymerization at room temperature. Furthermore, an oxygen-tolerant photoPISA strategy was also developed by adding GOx and glucose into the reaction, allowing the preparation of polymer nanoobjects in open air or multiwell plates. This method not only extends the application of polymerization-induced selfassembly, but also facilitates the formation of functional polymer nano-objects that are challenging to prepare by conventional RAFT-mediated emulsion polymerization.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.9b00007.

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Full experimental section and additional results (PDF).

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jianbo Tan: 0000-0002-5635-7178 Hao Sun: 0000-0001-9153-4021 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge support from the National Natural Science Foundation of China (Grant 21504017), Science and Technology Planning Project of Guangdong Province (Grant 2017A010103045), and Science and Technology Program of Guangzhou (Grant 201707010420). J.T. acknowledges the support from Pearl River Young Scholar.

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DOI: 10.1021/acsmacrolett.9b00007 ACS Macro Lett. 2019, 8, 205−212