Influence of Solvophilic Homopolymers on RAFT Polymerization-Induced Self-Assembly

Microwave Irradiation-Assisted Reversible Addition-Fragmentation Chain Transfer Polymerization-Induced Self-Assembly of pH-Responsive Diblock Copolymer Nanoparticles

Herein, we present a versatile platform for the synthesis of pH-responsive poly([N-(2-hydroxypropyl)]methacrylamide)-b-poly[2-(diisopropylamino)ethyl methacrylate] diblock copolymer (PHPMA-b-PDPA) nanoparticles (NPs) obtained via microwave-assisted reversible addition-fragmentation chain transfer polymerization-induced self-assembly (MWI-PISA). The N-(2-hydroxypropyl) methacrylamide (HPMA) monomer was first polymerized to obtain a macrochain transfer agent with polymerization degrees (DPs) of 23 and 51. Subsequently, using mCTA and 2-(diisopropylamino)ethyl methacrylate (DPA) as monomers, we successfully conducted MWI-PISA emulsion polymerization in aqueous solution with a solid content of 10 wt %. The NPs were obtained with high monomer conversion and polymerization rates. The resulting diblock copolymer NPs were analyzed by dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (cryo-TEM). cryo-TEM studies reveal the presence of only NPs with spherical morphology such as micelles and polymer vesicles known as polymersomes. Under the selected conditions, we were able to fine-tune the morphology from micelles to polymersomes, which may attract considerable attention in the drug-delivery field. The capability for drug encapsulation using the obtained in situ pH-responsive NPs, the polymersomes based on PHPMA₂₃-b-PDPA₁₀₀, and the micelles based on PHPMA₅₁-b-PDPA₁₀₀ was demonstrated using the hydrophobic agent and fluorescent dye as Nile red (NR). In addition, the NP disassembly in slightly acidic environments enables fast NR release.

In situ insight into the self-assembly evolution of ABA-type block copolymers in water during the gelation process using infrared spectroscopy and near-infrared spectroscopy

As a kind of thermo-responsive hydrogel, amphiphilic block copolymers are widely investigated. However, the molecular mechanism of their structural change during the gelation process is still limited. Here, a well-controlled triblock copolymer poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-dimethylacrylamide) (PDMAA-b-PDAAM-b-PDMAA) was synthesized. Its optical microrheology results suggest a gelation temperature range from 42 to 50 °C, showing a transition from viscosity to elasticity. The morphological transition from spheres to worms occurs. Temperature-dependent IR spectra through two-dimensional correlation spectroscopy (2D-COS) and the Gaussian fitting technique were analyzed to obtain the transition information of the molecular structure within the triblock copolymer. The N-way principal component analysis (NPCA) on the temperature-dependent NIR spectra was performed to understand the molecular interaction between water and the copolymer. The intramolecular hydrogen bonds within the hydrophobic PDAAM block tend to dissociate with temperature, resulting in improved hydration and a relative volume increase of the PDAAM block. The dissociation of intermolecular hydrogen bonds within the PDAAM block was the driving force for the morphological transition. Moreover, the hydrophilic PDMAA block dehydrates with temperature, and three stages can be found. The dehydration rate of the second stage with temperature from 42 to 50 °C was obviously higher than those in the lower (first stage) and higher (third stage) temperature ranges.

A3B-type miktoarm star polymer nanoassemblies prepared by reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization

The investigation on a series of A3B-type miktoarm star polymer assemblies by RAFT PISA has revealed the role of A3B architecture in delaying morphological transitions, and the formation of larger vesicles as well as other interesting morphologies.

Dispersion Polymerization versus Emulsifier-Free Emulsion Polymerization for Nano-Object Fabrication: A Comprehensive Comparison

Although the preparation of nano-objects by emulsifier-free controlled/living radical emulsion polymerization has drawn much attention, the morphologies of these formed objects are difficult to predict and to reproduce because of the much more complex nucleation mechanisms of emulsion polymerization compared to only one self-assembling nucleation mechanism of controlled radical dispersion polymerization. The present study compares dispersion polymerization with emulsifier-free emulsion polymerization in terms of nucleation mechanism, polymerization kinetics, and disappearance behavior of the macrochain transfer agent, gel permeation chromatograms curves of the obtained block copolymer as well as the structural and morphological differences between the produced nano-objects on the basis of published data. Moreover, the effects of the inherently heterogeneous nature of emulsion polymerization on the mechanism of reversible addition-fragmentation transfer polymerization and the nano-object morphology are examined, and efficient agitation and adequate solubility of the core-forming monomer in water are identified as the most crucial factors for the fabrication of nonspherical nano-objects.

Expanding the Scope of Polymerization-Induced Self-Assembly: Recent Advances and New Horizons

Over the past decade or so, polymerization-induced self-assembly (PISA) has become a versatile method for rational preparation of concentrated block copolymer nanoparticles with a diverse set of morphologies. Much of the PISA literature has focused on the preparation of well-defined linear block copolymers by using linear macromolecular chain transfer agents (macro-CTAs) with high chain transfer constants. In this review, a recent process is highlighted from an unusual angle that has expanded the scope of PISA including i) synthesis of block copolymers with nonlinear architectures (e.g., star block copolymer, branched block copolymer) by PISA, ii) in situ synthesis of blends of polymers by PISA, and iii) utilization of macro-CTAs with low chain transfer constants in PISA. By highlighting these important examples, new insights into the research of PISA and future impact these methods will have on polymer and colloid synthesis are provided.

How the Reactive End Group of Macro-RAFT Agent Affects RAFT-Mediated Emulsion Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly via reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization is an emerging method in which macro-RAFT agents are chain extended with hydrophobic monomers in water to form block copolymer nano-objects. However, almost all RAFT-mediated emulsion polymerizations are limited to AB diblock copolymers by using monofunctional macro-RAFT agents with non-reactive end groups. In this study, the first investigation on how the reactive end group of macro-RAFT agent affects RAFT-mediated emulsion polymerization is reported. Three macro-RAFT agents with different end groups are synthesized and employed in RAFT-mediated emulsion polymerization. Effects of end groups on morphologies of block copolymer nano-objects and polymerization process are studied. Block copolymer nano-objects prepared by using an asymmetric difunctional macro-RAFT agent can be functionalized by further chain extension on the surface. It is expected that the current study will not only expand the scope of RAFT-mediated emulsion polymerization, but also provide a novel strategy to prepare functional polymer nanoparticles.

Construction of Highly Ordered Glyco-Inside Nano-Assemblies through RAFT Dispersion Polymerization of Galactose-Decorated Monomer

Glyco-assemblies derived from amphiphilic sugar-decorated block copolymers (ASBCs) have emerged prominently due to their wide application, for example, in biomedicine and as drug carriers. However, to efficiently construct these glyco-assemblies is still a challenge. Herein, we report an efficient technology for the synthesis of glyco-inside nano-assemblies by utilizing RAFT polymerization of a galactose-decorated methacrylate for polymerization-induced self-assembly (PISA). Using this approach, a series of highly ordered glyco-inside nano-assemblies containing intermediate morphologies were fabricated by adjusting the length of the hydrophobic glycoblock and the polymerization solids content. A specific morphology of complex vesicles was captured during the PISA process and the formation mechanism is explained by the morphology of its precursor and intermediate. Thus, this method establishes a powerful route to fabricate glyco-assemblies with tunable morphologies and variable sizes, which is significant to enable the large-scale fabrication and wide application of glyco-assemblies.

Preparation of Block Copolymer Nano-Objects with Embedded β-Ketoester Functional Groups by Photoinitiated RAFT Dispersion Polymerization

Herein, a photoinitiated reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of 2-(acetoacetoxy)ethyl methacrylate (AEMA) in ethanol/water at room temperature for in situ preparation of β-ketoester-functionalized block copolymer nano-objects is reported. AEMA is also copolymerized with isobornyl methacrylate (IBOMA) to improve the colloidal stability of PIBOMA-based block copolymer nano-objects prepared by photoinitiated RAFT dispersion polymerization at low temperatures. A series of P(IBOMA-stat-AEMA)-based block copolymer nano-objects are prepared by changing reaction parameters. Finally, lanthanide-doped block copolymer nano-objects with luminescent and magnetic properties are also prepared based on the complexation of various lanthanide ions with the β-ketoester group. It is expected that the current study will provide a facile platform for the in situ preparation of β-ketoester-functionalized block copolymer nano-objects with different morphologies for specific applications.

Core-functionalized nanoaggregates: preparation via polymerization-induced self-assembly and their applications

Core-functionalized nanoaggregates can be prepared by a combination of polymerization-induced self-assembly (PISA) and post-polymerization modification.

Influence of single chain nanoparticle stabilizers on polymerization induced hierarchical self-assembly

Intramolecularly folded single chain nanoparticles (SCNPs) with steric character are used as stabilizers to construct a polymerization-induced self-assembly (PISA) formulation for the first time.

Light-intensity switch enabled nonsynchronous growth of fluorinated raspberry-like nanoparticles

Raspberry-like (RB) nanoparticles hold potential for diverse applications due to their hierarchical morphology. Here we developed a novel tandem synthetic approach of nonsynchronous growth based on photo-mediated reversible-deactivation radical polymerization, enabling simple, efficient and bottom-up synthesis of RB nanoparticles of uniform sizes at quantitative conversions of fluorinated monomers. Chain transfer agents of different chain lengths, concentrations and chemical compositions were varied to tune the diameter of RB particles. Importantly, fluorinated RB nanoparticles obtained with this method allow facile post modifications via both covalent bond formation and intermolecular physical interactions without disrupting the RB morphology. The facile nature of this method and versatility of the obtained fluorinated RB materials open new opportunities for the development of functional materials using nanoparticles.

Polymerization techniques in polymerization-induced self-assembly (PISA)

The development of controlled/“living” polymerization greatly stimulated the prosperity of the fabrication and application of block copolymer nano-objects.

Cross-linking approaches for block copolymer nano-assemblies via RAFT-mediated polymerization-induced self-assembly

This minireview summarizes the current cross-linking approaches to stabilize block copolymer nano-assemblies obtained via RAFT-mediated PISA process.

Unraveling the kinetics of the structural development during polymerization-induced self-assembly: decoupling the polymerization and the micelle structure

Upon extending a hydrophobic polymer chain from the end of a preceding hydrophilic chain in aqueous solutions, the resultant block copolymers may eventually undergo self-assembly.

Light-Triggered Reversible Slimming of Azobenzene-Containing Wormlike Nanoparticles Synthesized by Polymerization-Induced Self-Assembly for Nanofiltration Switches

Photoresponsive wormlike block copolymer nanoparticles (NPs) have potential applications in versatile fields, but their preparation suffers from narrow worm phase region and tedious approaches. In this work, azobenzene-containing wormlike NPs based on poly(methylacrylic acid)-b-poly(4-((4-butylphenyl)diazenyl)phenyl methacrylate) are prepared via polymerization-induced self-assembly at high solids concentration in ethanol. The pure wormlike NPs occupy a remarkably broad region in the morphological phase diagram because of the rigid nature of the core-forming block. These wormlike NPs expand resulting from trans-cis transformation upon UV irradiation, and slim near to the original state via visible light irradiation. The diameter and its variation amplitude of worms increase with the chain length of core-forming block. Moreover, a nanofiltration switch for rhodamine B is assembled to illustrate one of its potential applications by remote trigger using light.

Photoinitiated Polymerization-Induced Self-Assembly via Visible Light-Induced RAFT-Mediated Emulsion Polymerization

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 nano-objects 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.

Combining the power of heat and light: temperature-programmed photoinitiated RAFT dispersion polymerization to tune polymerization-induced self-assembly

A novel temperature-programmed photo-PISA method which combines the power of heat and light is developed for the preparation of a diverse set of morphologies.

In situ synthesis of PAA-b-PSt nano-assemblies via dispersion RAFT polymerization: effects of PEG in the medium

A facile and efficient approach was proposed to adjust BCP assemblies in PISA by introduction of PEG in the medium. Both PEG amount and molecular weight have significant effects on PAA-b-PSt micelles.