RAFT-mediated Polymerization-induced Self-assembly Research Articles

Polymerization-pH tailored RAFT-mediated polymerization-induced self-assembly for ice recrystallization inhibiting the investigation

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA) has been undergoing fast development currently, promoting research toward more diverse morphologies and more cutting-edge applications.

Perovskite photoinitiated RAFT-mediated polymerization-induced self-assembly for organic–inorganic hybrid nanomaterials

An efficient strategy is proposed to construct PQD/polymer organic–inorganic nanohybrids by PET-RAFT polymerization-mediated PISA and the nanohybrid assemblies can maintain excellent luminescence originating from PQDs with enhanced stability.

Synthesis of Multifunctional Polymersomes Prepared by Polymerization-Induced Self-Assembly.

Polymersomes are an exciting modality for drug delivery due to their structural similarity to biological cells and their ability to encapsulate both hydrophilic and hydrophobic drugs. In this regard, the current work aimed to develop multifunctional polymersomes, integrating dye (with hydrophobic Nile red and hydrophilic sulfo-cyanine5-NHS ester as model drugs) encapsulation, stimulus responsiveness, and surface-ligand modifications. Polymersomes constituting poly(N-2-hydroxypropylmethacrylamide)-b-poly(N-(2-(methylthio)ethyl)acrylamide) (PHPMAm-b-PMTEAM) are prepared by aqueous dispersion RAFT-mediated polymerization-induced self-assembly (PISA). The hydrophilic block lengths have an effect on the obtained morphologies, with short chain P(HPMAm)16 affording spheres and long chain P(HPMAm)43 yielding vesicles. This further induces different responses to H2O2, with spheres fragmenting and vesicles aggregating. Folic acid (FA) is successfully conjugated to the P(HPMAm)43, which self-assembles into FA-functionalized P(HPMAm)43-b-P(MTEAM)300 polymersomes. The FA-functionalized P(HPMAm)43-b-P(MTEAM)300 polymersomes entrap both hydrophobic Nile red (NR) and hydrophilic Cy5 dye. The NR-loaded FA-linked polymersomes exhibit a controlled release of the encapsulated NR dye when exposed to 10 mM H2O2. All the polymersomes formed are stable in human plasma and well-tolerated in MCF-7 breast cancer cells. These preliminary results demonstrate that, with simple and scalable chemistry, PISA offers access to different shapes and opens up the possibility of the one-pot synthesis of multicompartmental and responsive polymersomes.

Temperature-Responsive Lactic Acid-Based Nanoparticles by RAFT-Mediated Polymerization-Induced Self-Assembly in Water.

This work demonstrates for the first-time biobased, temperature-responsive diblock copolymer nanoparticles synthesized by reversible addition-fragmentation chain-transfer (RAFT) aqueous emulsion polymerization-induced self-assembly (PISA). Here, monomers derived from green solvents of the lactic acid portfolio, N,N-dimethyl lactamide acrylate (DMLA) and ethyl lactate acrylate (ELA), were used. First, DMLA was polymerized by RAFT aqueous solution polymerization to produce a hydrophilic PDMLA macromolecular chain transfer agent (macro-CTA), which was chain extended with ELA in water to form amphiphilic PDMLA-b-PELA diblock copolymer nanoparticles by RAFT aqueous emulsion polymerization. PDMLAx homopolymers were synthesized targeting degrees of polymerization, DPx from 25 to 400, with relatively narrow molecular weight dispersities (Đ < 1.30). The PDMLA64-b-PELAy diblock copolymers (DPy = 10-400) achieved dispersities, Đ, between 1.18 and 1.54 with two distinct glass transition temperatures (Tg) identified by differential scanning calorimetry (DSC). Tg(1) (7.4 to 15.7 °C) representative of PELA and Tg(2) (69.1 to 79.7 °C) of PDMLA. Dynamic light scattering (DLS) studies gave particle z-average diameters between 11 and 74 nm (PDI = 0.04 to 0.20). Atomic force microscopy (AFM) showed evidence of spherical particles when dispersions were dried at ∼5 °C and film formation when dried at room temperature. Many of these polymers exhibited a reversible lower critical solution temperature (LCST) in water with a concomitant increase in z-average diameter for the PDMLA-b-PELA diblock copolymer nanoparticles.

Multifunctional Layer-by-Layer Coating Based on a New Amphiphilic Block Copolymer via RAFT-Mediated Polymerization-Induced Self-Assembly Process.

In this hi-tech world, the "smart coatings" have sparked significant attention among materials scientists because of their versatile applications. Various strategies have been developed to generate smart coatings in the past 2 decades. The layer-by-layer (LbL) technique is the most commonly employed strategy to produce a smart coating for suitable applications. Here, we present a smart coating with healing, antifogging, and fluorescence properties fabricated by the LbL assembly of an anionic amphiphilic block copolymer latex and cationic inorganic POSS (polyhedral-oligomeric-silsesquioxane) nanoparticles. In this case, a new anionic block copolymer (BCP), {poly(sodium styrene sulfonate)-block-poly[2-(acetoacetoxy)ethyl methacrylate]}, (PSS-b-PAAEMA) was synthesized via surfactant-free RAFT-mediated emulsion polymerization using the PISA technique. The PSS-b-PAAEMA was characterized by 1H NMR, dynamic light scattering, scanning electron microscopy, and transmission electron microscopy analyses as well as by UV-vis and photoluminescence spectroscopy. For LbL coating fabrication, an amine-modified glass was successively dipped in the anionic latex and cationic POSS solution. The transparent coating exhibited good fluorescence properties under UV light (blue color). The antifogging performance of the coating was also investigated using both cold-warm and hot-vapor techniques. Additionally, the coating surface showed a significant healing activity with a healing efficiency of >75% through ionic interaction. Thus, this finding provides a simple low volatile organic compound (VOC) water-based LbL coating with multifunctional properties that can be a potential material for versatile applications.

Unimer Exchange Is not Necessary for Morphological Transitions in Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly (PISA) has established itself as a powerful and straightforward method to produce polymeric nano-objects of various morphologies in (aqueous) solution. Generally, spheres are formed in the early stages of polymerization that may evolve to higher order morphologies (worms or vesicles), as the solvophobic block grows during polymerization. Hitherto, the mechanisms involved in these morphological transitions during PISA are still not well understood. Combining a systematic study of a representative PISA system with rheological measurements, we demonstrate that-unexpectedly-unimer exchange is not necessary to form higher order morphologies during radical RAFT-mediated PISA. Instead, in the investigated aqueous PISA, the monomer present in the polymerization medium is responsible for the morphological transitions, even though it slows down unimer exchange.

H2O2-Responsive Nanocarriers Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly of N-(2-(Methylthio)ethyl)acrylamide for Biomedical Applications

H2O2-sensitive block copolymer nanoparticles (NPs) composed of a hydrophilic macro-chain transfer agent (macro-CTA) and a hydrophobic thioether-bearing block were prepared by polymerization-induced self-assembly (PISA) approach. The PISA process first involved the chain extension of poly((poly(ethylene glycol) methyl ether methacrylate)-co-(poly(ethylene glycol) methacrylate)) macro-CTA with a H2O2-responsive N-(2-(methylthio)ethyl)acrylamide (MTEAM) monomer, which self-assembled into P((PEGMA-co-PEGMAOH)-b-PMTEAM) block copolymer NPs. The polymerization kinetics indicated the evolution of particle size and morphology from spherical micelles, fused micelles, to vesicles over time. Upon incubation with 0.1 to 10 mM H2O2, spheres were fragmented due to the oxidation of the PMTEAM cores, thus transforming the hydrophobic thioethers into hydrophilic sulfoxides and disassociating the nanocarriers. 43% of the hydrophobic Nile red dye was encapsulated into the spherical micelles and demonstrated a controlled release in H2O2 incubation. Spherical micelles and vesicles displayed no cytotoxicity in MCF-7, DU145, and 22Rv1 cells. Both spheres and vesicles were efficiently internalized into MCF-7 cells, with spheres showing a higher level of uptake than vesicles due to the smaller sizes. In summary, PISA of P((PEGMA-co-PEGMAOH)-b-PMTEAM) allowed the direct formation and loading of hydrophobic dye into spherical micelles, which showed a controlled drug release in H2O2.

RAFT-mediated polymerization-induced self-assembly of cholic acid-derived monomer

RAFT-mediated polymerization-induced self-assembly of cholic acid-derived monomer

Polymerization-induced self-assembly of random bottlebrush copolymers

RAFT-mediated polymerization-induced self-assembly (PISA) was exploited to evaluating the self-assembly behavior of amphiphilic random P[PEGMA-co-(HEMA-g-PS)] bottlebrush copolymers.

Photoluminescent polymer cubosomes prepared by RAFT-mediated polymerization-induced self-assembly

The preparation of photoluminescent polymer assemblies with a wide range of morphologies, including spongosomes and cubosomes, via an efficient RAFT-mediated polymerization-induced self-assembly (RAFT-PISA) process, was demonstrated.

Pyridine-functional diblock copolymer nanoparticles synthesized via RAFT-mediated polymerization-induced self-assembly: effect of solution pH.

Polymerization-induced self-assembly (PISA) via reversible addition-fragmentation chain transfer (RAFT) polymerization has become widely recognized as a versatile and efficient strategy to prepare complex block copolymer nanoparticles with controlled morphology, size, and surface functionality. In this article, we report the preparation of cationic sterically-stabilized poly(2-vinylpyridine)-poly(benzyl methacrylate) (P2VP-PBzMA) diblock copolymer nanoparticles via RAFT-mediated PISA under aqueous emulsion polymerization conditions. It is demonstrated that the solution pH during PISA has a dramatic effect on the resulting P2VP-PBzMA nanoparticles, as judged by dynamic light scattering (DLS), disc centrifuge photosedimentometry (DCP) and transmission electron microscopy (TEM). Varying the solution pH results in the P2VP stabilizer having different solubilities due to protonation/deprotonation of the pyridine groups. This allows P2VP-PBzMA nanoparticles with tunable diameters to be prepared by altering the DP of the stabilizer (P2VP) and/or core-forming block (PBzMA), or simply by changing the solution pH for a fixed copolymer composition. For example, P2VP-PBzMA nanoparticles with larger diameters can be obtained at higher solution pH as the protonation degree of the P2VP stabilizer has a large effect on both the aggregation of polymer chains during the PISA process, and the resulting behavior of the diblock copolymer nanoparticles. Changing the dispersion pH post-polymerization has a relatively limited effect on particle diameter. Furthermore, aqueous electrophoresis studies indicate that these P2VP-PBzMA nanoparticles had good colloidal stability and high cationic charge (>30 mV) below pH 5 and can be dispersed readily over a wide pH range.

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA): current status and future directions.

Polymerization-induced self-assembly (PISA) combines polymerization and self-assembly in a single step with distinct efficiency that has set it apart from the conventional solution self-assembly processes. PISA holds great promise for large-scale production, not only because of its efficient process for producing nano/micro-particles with high solid content, but also thanks to the facile control over the particle size and morphology. Since its invention, many research groups around the world have developed new and creative approaches to broaden the scope of PISA initiations, morphologies and applications, etc. The growing interest in PISA is certainly reflected in the increasing number of publications over the past few years, and in this review, we aim to summarize these recent advances in the emerging aspects of RAFT-mediated PISA. These include (1) non-thermal initiation processes, such as photo-, enzyme-, redox- and ultrasound-initiation; the achievements of (2) high-order structures, (3) hybrid materials and (4) stimuli-responsive nano-objects by design and adopting new monomers and new processes; (5) the efforts in the realization of upscale production by utilization of high throughput technologies, and finally the (6) applications of current PISA nano-objects in different fields and (7) its future directions.

Segmented Copolymers Synthesized by Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization Using an Asymmetric Difunctional RAFT Agent and the Utilization in RAFT-Mediated Dispersion Polymerization

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) is an in situ growth method of increasing interest for the preparation of block copolymer nano-objects with diverse morphologies at high solids contents (10–50 wt %). Recent reports have shown that structures of multifunctional macro-RAFT agents can significantly affect RAFT-mediated PISA and the formed block copolymer nano-objects, but all these multifunctional macro-RAFT agents are limited to symmetric structures. In this study, we synthesized a novel difunctional RAFT agent with an asymmetric structure and employed in RAFT solution polymerization to prepare segmented macro-RAFT agents. Size exclusion chromatography (SEC) analysis showed that the redistribution of blocks occurred during RAFT polymerization, leading to the formation of segmented copolymers with different blocks (block number up to 4). Control experiments demonstrated that this redistribution process was derived from the unique structure of the asymmetric difunctional RAFT agent rather than monomers. The obtained segmented macro-RAFT agent was then used in RAFT-mediated dispersion polymerization to prepare well-defined block copolymer nano-objects. Owing to the unique structure of segmented block copolymers, shorter micellar nucleation was observed and a certain number of trithiocarbonate groups could be introduced on the surface of block copolymer nano-objects. The trithiocarbonate groups located on the surface of block copolymer nano-objects provide a landscape for further chain extension and functionalization. As a proof-of-concept experiment, vesicles loaded with silver nanoparticles were successfully prepared by in situ reduction of AgNO3 and employed as a catalyst to reduce methylene blue in the presence of NaBH4. We expect that this study will not only provide important mechanistic insights into RAFT polymerization mediated by multifunctional RAFT agents but also enable the preparation of functional block copolymer nano-objects.

In situ cross-linking in RAFT-mediated emulsion polymerization: Reshaping the preparation of cross-linked block copolymer nano-objects by polymerization-induced self-assembly

Large-scale preparation of cross-linked block copolymer nano-objects using polymerization-induced self-assembly (PISA) generally suffers from the limitation that high degrees of cross-linking in the early stage must be avoided. Herein, we demonstrate that the intrinsic monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization can be used to delay in situ cross-linking during PISA, allowing the preparation of cross-linked block copolymer nano-objects with high cross-linker contents. When using hydrophobic cross-linkers, the cross-linker along with monomer diffuses from monomer droplets to micelles gradually. When using hydrophilic cross-linkers, the cross-linker is prone to stay in water rather than diffuse into hydrophobic micellar cores. 1H NMR analysis confirmed the consumption behavior of cross-linkers during RAFT-mediated emulsion polymerization regardless of cross-linkers used. A variety of cross-linkers with different aqueous solubilities, symmetries, and functional groups were employed to prepare cross-linked block copolymer nano-objects. It is demonstrated that increasing the content of cross-linker promoted the formation of higher-order morphologies. We expect this study will not only expand the scope of RAFT-mediated PISA for in situ preparation of cross-linked block copolymer nano-objects, but also inspires researchers in this field to prepare novel polymer nanoparticles based on the unique mechanism of RAFT-mediated emulsion polymerization.

Switching between Thermal Initiation and Photoinitiation Redirects RAFT-Mediated Polymerization-Induced Self-Assembly

Reversible addition–fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) is an in situ growth method of growing interest for the preparation of well-defined bloc...

Type I Photoinitiator-Functionalized Block Copolymer Nanoparticles Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly.

Type I photoinitiators have been widely used in UV-vis curing technology for the fabrication of functional polymer materials such as coatings, inks, and adhesives. To overcome the drawbacks of using small molecular type I photoinitiators and expand the potential applications of UV-vis curing technology, attaching type I photoinitiators onto the surface of polymer colloids is an attractive strategy. Here we report a robust strategy for the efficient preparation of type I photoinitiator-functionalized block copolymer nanoparticles with various morphologies via aqueous reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA), in which the photoinitiating ability of the type I photoinitiator end group provides a landscape for further functionalization. These block copolymer nanoparticles could also be used as heterogeneous photoinitiators to generate hydrogels with nanoparticles embedded inside. Significantly, the properties and functionalities of these hydrogels could be further controlled by using different block copolymer nanoparticles. This study provides a robust strategy toward the preparation of type I photoinitiator-functionalized block copolymer nanoparticles with the capacity to be modified with varying functionalities.

Modification of cellulose through physisorption of cationic bio-based nanolatexes – comparing emulsion polymerization and RAFT-mediated polymerization-induced self-assembly

Investigation of film formation of cationically charged nanolatexes comprised of terpene-derived monomer synthesized with emulsion and RAFT-mediated polymerization induce self-assembly on cellulose.

Probing Thermoresponsive Polymerization-Induced Self-Assembly with Variable-Temperature Liquid-Cell Transmission Electron Microscopy

Summary We directly initiate and visualize the formation of polymeric nanomaterials via variable-temperature liquid-cell transmission electron microscopy (VT-LCTEM). With temperature control in the liquid cell, reversible addition-fragmentation chain transfer polymerization was thermally initiated, leading to the formation of amphiphilic block copolymers that assemble upon dispersion polymerization-induced self-assembly (PISA). In combination with traditional ex situ analyses, VT-LCTEM enabled not only the characterization of the nanoparticles in situ but also the observation of a thermal phase transition. Critically, because these assemblies form from thermoresponsive components, any temperature changes during sample preparation and analysis can alter morphologies, necessitating direct in situ characterization of reaction progression. We believe that the findings and the technique described herein will lead to unprecedented possibilities for the development and characterization of self-organizing soft matter.

RAFT-Mediated Polymerization-Induced Self-Assembly.

After a brief history that positions polymerization-induced self-assembly (PISA) in the field of polymer chemistry, this Review will cover the fundamentals of the PISA mechanism. Furthermore, this Review will also give an overview of some of the features and limitations of RAFT-mediated PISA in terms of the choice of the components involved, the nature of the nanoobjects that can be obtained and how the syntheses can be controlled, as well as some potential applications.

R-RAFT or Z-RAFT? Well-Defined Star Block Copolymer Nano-Objects Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) has served as a versatile platform for the large-scale preparation of block copolymer nano-objects with a diverse set of morphologies. However, almost all PISA formulations are focused on the syntheses of linear block copolymers rather than star block copolymers. Owing to the asymmetrical structure of the RAFT agent, herein, we report a direct comparison between Z-RAFT (the nonfragmenting group attached to the core) and R-RAFT (the fragmenting group attached to the core) strategies for preparing well-defined star block copolymer nano-objects via RAFT-mediated PISA. We showed that the Z-RAFT strategy is a more suitable strategy for the preparation of star block copolymer nano-objects without compromising the control over the molecular weight and morphology. A binary mixture of Z-type and R-type tetrafunctional macro-RAFT agents was used to control the morphologies of star block copolymer assemblies. The effect of numbers of the RAFT group on polymerization kinetics and morphologies of block copolymer nano-objects was also investigated in detail. Finally, (ABC)4 four-arm star triblock copolymer vesicles were prepared by seeded RAFT dispersion polymerization of solvophobic and solvophilic monomers using (AB)4 four-arm star diblock copolymer vesicles as seeds. This research not only expands the scope for preparing well-defined star block copolymer nano-objects but also provides important insights into the effect of the polymer architecture on RAFT-mediated PISA.