Visible Light-Mediated Polymerization-Induced Self-Assembly in the Absence of External Catalyst or Initiator

Recent Advances in RAFT Polymerization: Novel Initiation Mechanisms and Optoelectronic Applications

Reversible addition-fragmentation chain transfer (RAFT) is considered to be one of most famous reversible deactivation radical polymerization protocols. Benefiting from its living or controlled polymerization process, complex polymeric architectures with controlled molecular weight, low dispersity, as well as various functionality have been constructed, which could be applied in wide fields, including materials, biology, and electrology. Under the continuous research improvement, main achievements have focused on the development of new RAFT techniques, containing fancy initiation methods (e.g., photo, metal, enzyme, redox and acid), sulfur-free RAFT system and their applications in many fields. This review summarizes the current advances in major bright spot of novel RAFT techniques as well as their potential applications in the optoelectronic field, especially in the past a few years.

Expanding the Scope of Polymerization-Induced Self-Assembly: Z-RAFT-Mediated Photoinitiated Dispersion Polymerization

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/cm²) 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 NaBH₄. 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.

Rational Design of a Green-Light-Mediated Unimolecular Platform for Fast Switchable Acidic Sensing

A controllable sensing ability strongly connects to complex and precise events in diagnosis and treatment. However, imposing visible light into the molecular-scale mediation of sensing processes is restricted by the lack of structural relevance. To address this critical challenge, we present the rational design, synthesis, and in vitro studies of a novel cyanostyryl-modified azulene system for green-light-mediated fast switchable acidic sensing. The advantageous features of the design include a highly efficient green-light-driven Z/E-isomerization (a quantum yield up to 61.3%) for fast erasing chromatic and luminescent expressions and a superior compatibility with control of ratiometric protonation. Significantly, these merits of the design enable the development of a microfluidic system to perform a green-light-mediated reusable sensing function toward a gastric acid analyte in a miniaturized platform. The results may provide new insights for building future integrated green materials.

Simple and Green Strategy for the Synthesis of "Pathogen-Mimetic" Glycoadjuvant@AuNPs by Combination of Photoinduced RAFT and Bioinspired Dopamine Chemistry

Innate immune responses recognizing pathogen associated molecular patterns (PAMPs) play a crucial role in adaptive immunity. Toll-like receptors (TLRs) and C-type lectin receptors (CLRs) contribute to antigen capture, uptake, presentation and activation of immune responses. In this contribution, metal-free reversible addition-fragmentation chain transfer (RAFT) polymerization of N-3,4-dihydroxybenzenethyl methacrylamide (DMA) and 2-(methacrylamido) glucopyranose (MAG) under sunlight irradiation using 2-cyanoprop-2-yl-α-dithionaphthalate (CPDN) as iniferter agent, can be employed to fabricate the multivalent glycopolymer containing bioresponsive sugar group and multifunctional catechol functionalities. The polymerization behavior is investigated and it presents controlled features. Moreover, bioinspired dopamine chemistry can be successfully utilized to form in situ glycopolymer-coated gold nanoparticles (AuNPs) without the need of additional reducing reagent, design "pathogen-mimetic" glycoadjuvant recognized by both CLRs and TLRs. The synthetic glycoadjuvant is found to enhance the adjuvant activity as "infected signals" in vitro.

Light-induced evolution of microaggregates: transformation to vesicles, cyclic growth and collapse and vesicle fusion

The self-assembled dynamic microaggregates were obtained in one pot via PISA and underwent visible light-induced evolutionary behaviors in the presence of nile red or rhodamine.

Light-mediated one-pot synthesis of an ABC triblock copolymer in aqueous solution via RAFT and the effect of pH on copolymer self-assembly

We present the triblock copolymer self-assembly resulting into different morphologies that occurred during the polymerization of a hydrophobic third block in aqueous solution.

PET-RAFT polymerisation: towards green and precision polymer manufacturing

Photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) process has opened up a new way of precision polymer manufacturing to satisfy the concept of green chemistry.

Preparation of semifluorinated poly(meth)acrylates by improved photo-controlled radical polymerization without the use of a fluorinated RAFT agent: facilitating surface fabrication with fluorinated materials

Semifluorinated poly(meth)acrylates are prepared under both organocatalyzed and catalyst-free photo-controlled radical polymerization conditions from simple RAFT agents.

Photoinduced controlled radical polymerization of methyl acrylate and vinyl acetate by xanthate

A block copolymer of PMA-b-PVAc was successfully synthesized using photo-induced RAFT polymerization with a xanthate.

Synthesis of poly(ionic liquid)-based nano-objects with morphological transitionsviaRAFT polymerization-induced self-assembly in ethanol

A full range of morphologies including spheres, worms and vesicles was observed in poly(ionic liquid)-based block copolymer nano-objectsviaethanolic dispersion polymerization.

In situ glyco-nanostructure formulation via photo-polymerization induced self-assembly

A broad set of advanced glyco-nanostructures, rarely obtained as vesicles or never reported as wormlike micelles, is obtained using photo-initiated Polymerization-Induced Self-Assembly (Photo-PISA).

Self-Assembly of Cellulose Oligomers into Nanoribbon Network Structures Based on Kinetic Control of Enzymatic Oligomerization

The ability to chemically synthesize desired molecules followed by their in situ self-assembly in reaction solution has attracted much attention as a simple and environmentally friendly method to produce self-assembled nanostructures. In this study, α-d-glucose 1-phosphate monomers and cellobiose primers were subjected to cellodextrin phosphorylase-catalyzed reverse phosphorolysis reactions in aqueous solution in order to synthesize cellulose oligomers, which were then in situ self-assembled into crystalline nanoribbon network structures. The average degree-of-polymerization (DP) values of the cellulose oligomers were estimated to be approximately 7-8 with a certain degree of DP distribution. The cellulose oligomers crystallized with the cellulose II allomorph appeared to align perpendicularly to the base plane of the nanoribbons in an antiparallel manner. Detailed analyses of reaction time dependence suggested that the production of nanoribbon network structures was kinetically controlled by the amount of water-insoluble cellulose oligomers produced.

Controlling the generation of bilayer and multilayer vesicles in block copolymer/epoxy blends by a slow photopolymerization process

Vesicles are a highly attractive morphology to achieve in micellar dispersions of block copolymers (BCP) in epoxy thermosets due to the fact that small amounts can affect a large volume fraction of the matrix, a fact that is important for toughening purposes. However, generating vesicles in epoxy matrices requires operating in a narrow range of formulations and processing conditions. In this report, we show that block-copolymer vesicles dispersed in an epoxy matrix could be obtained through a sphere-to-cylinder-to-vesicle micellar transition induced by visible-light photopolymerization at room temperature. A 10 wt% colloidal solution of poly(ethylene-co-butene)-block-poly(ethylene oxide) (PEB-b-PEO) block copolymer (BCP) in an epoxy monomer (DGEBA) self-assembled into spherical micelles as shown by small-angle X-ray scattering (SAXS). During a slow photopolymerization of the epoxy monomer carried out at room temperature, a sphere-to-cylinder-to-vesicle transition took place as revealed by in situ SAXS and TEM images. This was driven by the tendency of the system to reduce the local interfacial curvature as a response to a decrease in the miscibility of PEO blocks in the polymerizing epoxy matrix. When the BCP concentration was increased from 10 to 20 and 40 wt%, the final structure evolved from bilayer vesicles to multilayer vesicles and to lamellae, respectively. In particular, for 20 wt% PEB-b-PEO, transient structures such as partially fused multilayered vesicles were observed by TEM, giving insight into the growth mechanism of multilayer vesicles. On the contrary, when a relatively fast thermal polymerization was performed at 80 °C, the final morphology consisted of kinetically trapped spherical and cylindrical micelles. Hopefully, this study will lead to new protocols for the preparation of vesicles dispersed in epoxy matrices in a controlled way.

ROMPISA: Ring-Opening Metathesis Polymerization-Induced Self-Assembly

Herein we report a polymerization-induced self-assembly (PISA) process with ring-opening metathesis polymerization (ROMP). We utilize a peptide-based norbornenyl monomer as a hydrophobic unit to provide a range of nanostructures at room temperature yet at high solids concentrations of 20 wt % in combination with an oligoethylene glycol based norbornenyl monomer. Evaluation of the polymerizations under mild conditions highlight that good control is maintained along with high monomer conversion of greater than 99%, indicating that the living polymerization is unaffected during the PISA process. The demonstration broadens the scope of the PISA process to a new living polymerization methodology toward the development of easily accessible and highly functionalized nanostructures in situ.

Facile One-Pot Synthesis of Functional Giant Polymeric Vesicles Controlled by Oscillatory Chemistry

We introduce a novel application of an oscillatory chemical reaction to the synthesis of block copolymers. The Belousov-Zhabotinsky (B-Z) reaction is coupled with the polymerization of an amphiphilic block copolymer. Radicals generated in the B-Z reaction initiate the polymerization between a polyethylene glycol (PEG) macroreversible addition-fragmentation chain-transfer agent and butyl acrylate monomers. The attachment of a hydrophobic block on PEG leads to self-assembly and formation of spherical micelles. The nanoscale micelles transform into submicrometer vesicles and grow to giant vesicles as a consequence of the oscillatory behavior of the B-Z reaction. The one-pot synthesis of an amphiphilic di-block copolymer and retention of oscillatory behavior for the B-Z reaction with the formation of giant vesicles bring a new insight into possible pathways for the synthesis of active functional microreactors in the range from hundreds of nanometers to tens of micrometers.

Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA): New Insights and Opportunities

The polymerization-induced self-assembly (PISA) process is a useful synthetic tool for the efficient synthesis of polymeric nanoparticles of different morphologies. Recently, studies on visible light initiated PISA processes have offered a number of key research opportunities that are not readily accessible using traditional thermally initiated systems. For example, visible light mediated PISA (Photo-PISA) enables a high degree of control over the dispersion polymerization process by manipulation of the wavelength and intensity of incident light. In some cases, the final nanoparticle morphology of a single formulation can be modulated by simple manipulation of these externally controlled parameters. In addition, temporal (and in principle spatial) control over the Photo-PISA process can be achieved in most cases. Exploitation of the mild room temperature polymerizations conditions can enable the encapsulation of thermally sensitive therapeutics to occur without compromising the polymerization rate and their activities. Finally, the Photo-PISA process can enable further mechanistic insights into the morphological evolution of nanoparticle formation such as the effects of temperature on the self-assembly process. The purpose of this mini-review is therefore to examine some of these recent advances that have been made in Photo-PISA processes, particularly in light of the specific advantages that may exist in comparison with conventional thermally initiated systems.

Comparison of photo- and thermally initiated polymerization-induced self-assembly: a lack of end group fidelity drives the formation of higher order morphologies

Polymerization-induced self-assembly (PISA) is an emerging industrially relevant technology, which allows the preparation of defined and predictable polymer self-assemblies with a wide range of morphologies. In recent years, interest has turned to photoinitiated PISA processes, which show markedly accelerated reaction kinetics and milder conditions, thereby making it an attractive alternative to thermally initiated PISA. Herein, we attempt to elucidate the differences between these two initiation methods using isothermally derived phase diagrams of a well-documented poly(ethylene glycol)-b-(2-hydroxypropyl methacrylate) (PEG-b-HPMA) PISA system. By studying the influence of the intensity of the light source used, as well as an investigation into the thermodynamically favorable morphologies, the factors dictating differences in the obtained morphologies when comparing photo- and thermally initiated PISA were explored. Our findings indicate that differences in a combination of both reaction kinetics and end group fidelity led to the observed discrepencies between the two techniques. We find that the loss of the end group in photoinitiated PISA drives the formation of higher order structures and that a morphological transition from worms to unilamellar vesicles could be induced by extended periods of light and heat irradiation. Our findings demonstrate that PISA of identical block copolymers by the two different initiation methods can lead to structures that are both chemically and morphologically distinct.

Artificially Smart Vesicles with Superior Structural Stability: Fabrication, Characterizations, and Transmembrane Traffic

Intelligent vesicles are fabricated at up to 30% solid content via an approach of polymerization-induced self-assembly and reorganization (PISR). Upon irradiation with UV light (365 nm), light-triggered dimerization of the coumarin moieties anchored in the membrane leads to the membrane cross-linking of the vesicles, which endows the vesicles with superior structural stability. Due to the tertiary amine groups in the membrane, the vesicles go through a swelling/deswelling change upon switching the pH values. In acidic aqueous solution, the pores in the membrane of vesicles are opened, which is beneficial for transmembrane traffic. The pore size in the membrane of vesicles is in accordance with the extent of membrane cross-linking, which can be conveniently regulated by the irradiation time of UV light (365 nm). The size range of the substance for transmembrane traffic is effectively enlarged; even 15 nm gold nanoparticles can be postloaded into the vesicles with lower extents of the membrane cross-linking through the diffusion method. Although the pores in the vesicle membrane are opened in acidic aqueous solution, transmembrane traffic is inhibited for the electropositive substance because of electrostatic repulsion but is allowed for the electronegative substance. These reported vesicles herein may be the smartest artificial vesicles to date due to their multiple selective permeability.

Polymerization-Induced Self-Assembly of Homopolymer and Diblock Copolymer: A Facile Approach for Preparing Polymer Nano-Objects with Higher-Order Morphologies

Polymerization-induced self-assembly of homopolymer and diblock copolymer using a binary mixture of small chain transfer agent (CTA) and macromolecular chain transfer agent (macro-CTA) is reported. With this system, homopolymer and diblock copolymer were formed and chain extended at the same time to form polymer nano-objects. The molar ratio of homopolymer and diblock copolymer had a significant effect on the morphology of the polymer nano-objects. Porous vesicles, porous nanospheres, and micron-sized particles with highly porous inner structure were prepared by this method. We expect that this method will greatly expand the promise of polymerization-induced self-assembly for the synthesis of a range of polymer nano-objects with unique morphologies.

Thermoresponsive gels directly obtained via visible light-mediated polymerization-induced self-assembly with oxygen tolerance

A thermoresponsive reversible hydrogel is developed by PET-RAFT mediated PISA in aqueous solution at room temperature without deoxygenation.

In situ synthesis of the Ag/poly(4-vinylpyridine)-block-polystyrene composite nanoparticles by dispersion RAFT polymerization

A new method for the synthesis of metal/block-copolymer nanocomposites of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) and Ag nanoparticles by dispersion RAFT polymerization is proposed.

In situ synthesis of a self-assembled AB/B blend of poly(ethylene glycol)-b-polystyrene/polystyrene by dispersion RAFT polymerization

A diblock-copolymer/homopolymer self-assembled blend was synthesized through dispersion RAFT polymerization, and its morphology changed with a decreasing ratio of diblock-copolymer/homopolymer.

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).

Opportunities for dual RDRP agents in synthesizing novel polymeric materials

Dual RDRP agents provide access to new polymeric materials by combining ATRP, NMP, and RAFT polymerization without end group transformations.

Synthesis of molecularly imprinted polymers by photo-iniferter polymerization under visible light

A new prospect for the synthesis of molecularly imprinted polymers: photo-iniferter polymerization under visible light.

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 RAFT dispersion polymerization of styrene and 4-vinylpyridine in methanol/water at 70 °C. The polymerization was mediated by a binary mixture of DDMAT and mPEG₄₅-DDMAT.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Application of oxygen tolerant PET-RAFT to polymerization-induced self-assembly

The inhibitory effects of molecular oxygen in PET-RAFT polymerization can be overcome by the addition of singlet oxygen quenchers. This oxygen tolerant approach is compatible with a range of organic solvents and can be used to synthesize nanoparticles according to a PISA process.

Oxygen tolerant photopolymerization for ultralow volumes

A benchtop approach is developed for the synthesis of various polymeric architectures using an aqueous Reversible Addition–Fragmentation chain Transfer (RAFT) photopolymerization technique.

Synthesis of polymeric nano-objects of various morphologies based on block copolymer self-assembly using microporous membranes

Polymeric nano-objects of a range of morphologies have been prepared using a novel approach based on the use of microporous membranes for mixing of a solvent (containing a diblock copolymer) and a non-solvent.

Visible-light-induced synthesis of polymers with versatile end groups mediated by organocobalt complexes

Synthesis of polymers with well-defined functional groups at α and ω ends by using carefully designed organocobalt complexes has been accomplished.

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

Photoinitiated polymerization-induced self-assembly (photo-PISA) is utilized to investigate the sole effect of reaction temperature on PISA.

Polymerization induced self-assembly: tuning of morphology using ionic strength and pH

It is demonstrated how the morphology of polymeric nanoparticles produced via polymerization-induced self-assembly (PISA) in dispersion can be conveniently tuned via the pH and ionic strength.

Photo-responsive polymers: synthesis and applications

Photo-responsive polymers are able to change their structure, conformation and properties upon light irradiation.

RAFT iniferter polymerization in miniemulsion using visible light

Methodology for the successful implementation of RAFT (4-cyano-4[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA)) iniferter polymerization of butyl methacrylate in miniemulsion using visible light (green light; λ_max = 530 nm) has been developed.

Synthesis of Hydrogen-Bonded Pore-Switchable Cylindrical Vesicles via Visible-Light-Mediated RAFT Room-Temperature Aqueous Dispersion Polymerization

Analogous to cellulose, polymers whose monomer units possess both hydrogen donators and acceptors are generally insoluble in ambient water because of hydrogen bonding (HB). Herein we present stimuli-responsive long aqueous cylindrical vesicles (nanotubes) synthesized directly using HB-driven polymerization-induced self-assembly (PISA) under visible-light-mediated RAFT aqueous dispersion polymerization at 25 °C. The PISA undergoes an unprecedented film/silk-to-ribbon-to-vesicle transition and films/silks/ribbons formed at low DPs (∼25-85) of core-forming block in free-flowing aqueous solution. Pore-switchable nanotubes are synthesized by electrostatic repulsive perturbation of the HB association in anisotropic vesicular membranes via inserting minor ionized monomer units into the core-forming block. These nanotubes are synthesized at >35% solids, and tubular membranes are more sensitive than spherical counterparts in response to aqueous surroundings. This facile, robust, and general strategy paves a new avenue toward scale-up production of advanced intelligent nanomaterials.