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.
Polymerization-induced self-assembly via reversible addition–fragmentation transfer (RAFT)-mediated emulsion polymerization has served as a versatile platform for scalable preparation of well-defined block copolymer nanoparticles. However, kinetically trapped spherical micelles rather than higher-order morphologies are typically prepared by RAFT-mediated emulsion polymerization. Moreover, the mechanism for morphological evolution under RAFT-mediated emulsion polymerization conditions is still unclear. Herein, we report a redox-initiated RAFT-mediated emulsion polymerization of methacrylic monomers at relatively low temperatures. A diverse set of morphologies have been prepared by using glycidyl methacrylate (GlyMA) as the core-forming monomer. Effects of reaction temperature, molecular weight of macro-RAFT agent, degree of polymerization of PGlyMA, and monomer concentration on RAFT-mediated emulsion polymerization have been studied in detail. To give more insights into the mechanism of morphological evolution, other methacrylic monomers were also employed for RAFT-mediated emulsion polymerization. Finally, taking advantage of the intrinsic mechanism of RAFT-mediated emulsion polymerization, cross-linking has been explored for the preparation of higher-order morphologies. The current study not only expands the scope of RAFT-mediated emulsion polymerization for preparing various block copolymer nano-objects but also provides important insights into the morphological evolution under RAFT-mediated emulsion polymerization conditions.
Enzyme catalysis is a mild, efficient, and selective technique that has many applications in organic synthesis as well as polymer synthesis. Here, a novel enzyme-catalysis-induced reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization for preparing AB diblock copolymer nano-objects with complex morphologies at room temperature is described. Taking advantage of the room-temperature feature, it is shown that pure, worm-like polymer nano-objects can be readily prepared by just monitoring the viscosity. Moreover, it is demonstrated that inorganic nanoparticles and proteins can be loaded in situ into vesicles by this method. Finally, a novel oxygen-tolerant RAFT-mediated dispersion polymerization initiated by enzyme cascade reaction that can be carried out in open vessels is developed. The enzyme-initiated RAFT dispersion polymerization provides a facile platform for the synthesis of various functional polymer nano-objects under mild conditions.
Cylindrical micelles formed by the self-assembly of block copolymers are of interest for a wide range of applications. In this study, aqueous seeded photoinitiated polymerization-induced self-assembly (photo-PISA) is developed for the preparation of cylindrical block copolymer micelles with patchy structures at high solids contents. Cross-linked cylindrical block copolymer micelles prepared by photo-PISA are used as seeds for further chain extension. Surface roughness of the patchy cylindrical block copolymer micelles can be controlled by varying degree of polymerization (DP) of the third block. The obtained patchy cylindrical micelles can be further functionalized via the modification of the third block. Due to the high solids content of patchy cylindrical micelles prepared by seeded photo-PISA (10% w/w or higher), we expect that this study will greatly expand the promise of PISA for the large-scale preparation of cylindrical micelles with well-defined structures.
In this communication, we developed the first well-controlled Z-RAFT (RAFT = reversible addition− fragmentation chain transfer) mediated polymerization-induced self-assembly (PISA) formulation based on photoinitiated RAFT dispersion polymerization of tert-butyl acrylate (tBA) in ethanol/water (60/40, w/w) at room temperature using a Z-type macromolecular chain transfer agent (macro-CTA). Polymerizations proceeded rapidly via the exposure of visible-light irradiation (405 nm, 0.45 mW/cm 2 ) with high monomer conversion (>95%) being achieved within 1 h. A variety of polymer nano-objects (spheres, worms, and vesicles) with narrow molar mass distributions were prepared by this Z-RAFT mediated PISA formulation. Silver nanoparticles were loaded with the vesicles via in situ reduction, which can be used as a catalyst for the reduction of methylene blue (MB) in the presence of NaBH 4 . Finally, gel permeation chromatography (GPC) analysis demonstrated that the corona block and the core-forming block could be cleaved by treating with excess initiator. This novel PISA formulation will greatly expand the scope of PISA and provide more mechanistic insights into the PISA research.
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