Jianbo Tan

Room temperature synthesis of poly(poly(ethylene glycol) methyl ether methacrylate)-based diblock copolymer nano-objects via Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA)

The photoinitiated polymerization-induced self-assembly (photo-PISA) of 2-hydroxypropyl methacrylate (HPMA) is conducted in water by using poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) based macro-RAFT agents. Polymerizations were carried out at room temperature via exposure to visible light irradiation, and quantitative monomer conversions (>99%) were achieved within 30 min of visible light irradiation. A remarkably diverse set of complex morphologies (spheres, worms, and vesicles) have been prepared by aqueous photo-PISA under mild conditions (water medium, room temperature, and visible light). The morphology of nano-objects can be tuned by changing the reaction parameters (e.g. degree of polymerization, solids concentration), and two detailed phase diagrams were constructed. The polymerization can be activated or deactivated by a simple “ON/OFF” switch of the light source. A thermo-responsive behavior of PPEGMA14-PHPMA200 nanoparticles prepared at 15% w/w was investigated by changing the temperature from 25 °C to 4 °C.

An insight into aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) for the preparation of diblock copolymer nano-objects

A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is used for aqueous reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) via photoinitiation or thermal initiation. Kinetic studies showed that the rate of polymerization of photo-PISA was much faster than that of thermally initiated PISA, both at the homogeneous polymerization stage and the heterogeneous polymerization stage. The effect of light intensity on photo-PISA was investigated, which showed that increasing light intensity led to faster polymerization behavior. In virtue of the temperature-insensitive property of the photoinitiator, the sole effect of reaction temperature on PISA was studied in detail for the first time. Transmission electron microscopy (TEM) measurements indicated that higher reaction temperature facilitated the formation of higher order morphologies. Finally, a one-pot photoinitiated polymerization was conducted in water to prepare diblock copolymer nano-objects with different morphologies (spheres, worms, and vesicles).

Facile Preparation of CO2‐Responsive Polymer Nano‐Objects via Aqueous Photoinitiated Polymerization‐Induced Self‐Assembly (Photo‐PISA)

Carbon dioxide (CO2 )-responsive polymer nano-objects are prepared by photoinitiated reversible addition-fragmentation chain transfer dispersion polymerization of 2-hydroxypropyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in water at room temperature using a poly(poly(ethylene glycol) methyl ether methacrylate) macromolecular chain transfer agent. Kinetic studies confirm that full monomer conversions are achieved in all cases within 10 min of visible-light irradiation (405 nm, 0.5 mW cm-2 ). The effect of DMAEMA on the polymerization is studied in detail, and pure higher order morphologies (worms and vesicles) are prepared by this particular formulation. Finally, CO2 -responsive property of the obtained vesicles is investigated by dynamic light scattering, visual appearance, and transmission electron microscope.

Facile preparation of hybrid vesicles loaded with silica nanoparticles via aqueous photoinitiated polymerization-induced self-assembly

We report a room-temperature photoinitiated polymerization-induced self-assembly (photo-PISA) of 2-hydroxypropyl methacrylate (HPMA) in the presence of silica nanoparticles using a poly(ethylene glycol) methyl ether (mPEG) macromolecular chain transfer agent (macro-CTA). Hybrid vesicles loaded with silica nanoparticles were obtained by this one-pot approach. The solids content of the polymer vesicles can be up to 25% w/w. A control experiment was conducted to prove that free silica nanoparticles can be removed via centrifugation-redispersion. Finally, CO2-responsive hybrid vesicles were prepared by photo-PISA of HPMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Silica nanoparticles were subsequently released from the vesicles via CO2 bubbling at room temperature.

Rapid synthesis of well-defined all-acrylic diblock copolymer nano-objects via alcoholic photoinitiated polymerization-induced self-assembly (photo-PISA)

A series of well-defined all-acrylic poly(hydroxyethyl acrylate)-poly(isobornyl acrylate) (PHEA-PIBOA) diblock copolymer nano-objects were prepared by photoinitiated polymerization-induced self-assembly (photo-PISA) of isobornyl acrylate in ethanol/water at 40 °C using poly(hydroxyethyl acrylate)-based macromolecular chain transfer agents (macro-CTAs). Polymerizations proceeded rapidly upon exposure to visible light irradiation (λmax = 405 nm, 0.46 mW cm−2) with high monomer conversion being achieved within 30 min. Gel permeation chromatography (GPC) demonstrated that good control was maintained throughout the photo-PISA process, and the final block copolymers exhibited relatively low polydispersities (Mw/Mn ≤ 1.55). By virtue of the high Tg value of PIBOA, a diverse set of block copolymer nano-objects having different morphologies (e.g. spheres, worms, and vesicles) were prepared and characterized by conventional transmission electron microscopy (TEM). Two phase diagrams were constructed by varying the DP of the PIBOA block or monomer concentration or the DP of the PHEA macro-CTA. Worm-like micelles were prepared by monitoring the viscosity of the reaction mixture in a proof-of-concept experiment. Finally, poly(acrylic acid) (PAA) and poly(2-(dimethylamino)ethyl acrylate) (PDMAEA) macro-CTAs were also utilized to mediate the photo-PISA process, demonstrating the versatility of this method.

Adding a solvophilic comonomer to the polymerization-induced self-assembly of block copolymer and homopolymer: a cooperative strategy for preparing large compound vesicles

We report a reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of styrene (St) and 4-vinylpyridine (4VP) in methanol/water at 70 °C. The polymerization was mediated by a binary mixture of S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetic acid) trithiocarbonate (DDMAT) and monomethoxy poly(ethylene glycol)-based macromolecular RAFT agent (mPEG45-DDMAT). By varying the molar ratio of [St]0/[4VP]0, polymer nano-objects of different morphologies (porous vesicles, large compound vesicles (LCVs), and lamellae) were formed. Transmission electron microscopy (TEM) observations demonstrated that LCVs were formed by further aggregation and reorganization of vesicles during the process. Effects of [mPEG45-DDMAT]/[DDMAT] molar ratio, methanol/water ratio, and degree of polymerization (DP) of the core-forming block on the assemblies were also studied in detail. Ag@mPEG45-P(St108-co-4VP24)/P(St108-co-4VP24) LCVs were prepared by in situ reduction of AgNO3, as confirmed by TEM and UV-vis measurements. The obtained Ag@mPEG45-P(St108-co-4VP24)/P(St108-co-4VP24) LCVs exhibited catalytic activity for the catalysis of methylene blue (MB) using NaBH4.

Enzyme‐PISA: An Efficient Method for Preparing Well‐Defined Polymer Nano‐Objects under Mild 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.

Photoinitiated Seeded RAFT Dispersion Polymerization: A Facile Method for the Preparation of Epoxy-Functionalized Triblock Copolymer Nano-Objects

In this study, a novel photoinitiated seeded reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization is developed for the preparation of epoxy-functionalized triblock copolymer nano-objects at room temperature. Epoxy-functionalized worms and vesicles prepared by photoinitiated RAFT dispersion polymerization of glycidyl methacrylate are used as seeds for chain extension by photoinitiated seeded RAFT dispersion polymerization of methacrylic and acrylic monomers. Good control is maintained during the polymerization with a high polymerization rate. Pure triblock copolymer worms can be prepared by the photoinitiated seeded RAFT dispersion polymerization with a broad degree of polymerization range of the third block. The room temperature feature of photoinitiated seeded RAFT dispersion polymerization is critical to ensure the survival of epoxy moiety after the polymerization. The obtained triblock copolymer nano-objects can be cross-linked by reacting with a diamine. Finally, cross-linked worms are used as the stationary phase of chromatography for selective separation of organic dyes from water.

Ketone-Functionalized Polymer Nano-Objects Prepared via Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA) Using a Poly(diacetone acrylamide)-Based Macro-RAFT Agent

Herein, ketone-functionalized diblock copolymer nano-objects are prepared by photoinitiated reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of tert-butyl acrylate (tBA) using a poly(diacetone acrylamide) (PDAAM)-based macromolecular RAFT (macro-RAFT) agent in ethanol/water (60/40, w/w) at room temperature. A high polymerization rate is observed via the exposure of visible light (λmax = 405 nm, 0.45 mW cm-2 ) with near quantitative monomer conversion being achieved within 60 min. A morphological phase diagram is constructed by changing the degree of polymerization (DP) of PtBA and the monomer concentration. The morphologies of polymer nano-objects are further tuned by incorporating isobornyl acrylate (IBOA) into the core-forming block. The ketone-functionalized diblock copolymer nano-objects can be shell-cross-linked by reacting with a diamine. Finally, the shell-cross-linked polymer nano-objects are further hydrolyzed and employed as a template for the synthesis of silver composites.

Enzyme catalysis-induced RAFT polymerization in water for the preparation of epoxy-functionalized triblock copolymer vesicles

Enzyme catalysis is a mild and efficient technique that has been widely used in organic chemistry and polymer chemistry. In this work, enzyme catalysis-induced aqueous reversible addition–fragmentation chain transfer (RAFT) polymerization was conducted at room temperature for the preparation of a series of epoxy-functionalized triblock copolymer vesicles. Specifically, poly(glycerol monomethacrylate)-b-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles were first prepared via enzyme-initiated aqueous RAFT dispersion polymerization, and subsequently used as seeds for chain extension of glycidyl methacrylate (GlyMA) via enzyme-initiated seeded RAFT emulsion polymerization. Nanoscale phase separation was observed at higher degree of polymerization (DP) of PGlyMA. The room temperature feature of enzyme-initiated RAFT polymerization is critical to ensure the survival of epoxy groups after the polymerization. The obtained triblock copolymer vesicles were evaluated as an efficient Pickering emulsifier for hexane-in-water emulsions. In addition, the triblock copolymer vesicles were found to be tolerant to the challenge of surfactant in water. Finally, the epoxy groups in the vesicular membrane were utilized to react with ethylene diamine, allowing the preparation of cross-linked vesicles as well as silver composite vesicles.