Scalable and uniform 1D nanoparticles by synchronous polymerization, crystallization and self-assembly

Efficient Energy Funneling in Spatially Tailored Segmented Conjugated Block Copolymer Nanofiber-Quantum Dot or Rod Conjugates

Hybrid systems composed of conjugated polymers and inorganic semiconductor nanocrystals such as quantum dots (QDs) and nanorods (QRs) represent highly desirable multifunctional materials for applications from energy harvesting to light emission and sensing. Herein, we describe energy transfer studies between low-dispersity segmented conjugated polymer micellar nanofibers integrated with quantum dots that are spatially confined to discrete regions in the hybrid assembly via noncovalent interactions. The nanofibers were prepared from diblock copolymers with a crystallizable poly(di-n-hexylfluorene) (PDHF) core-forming block and different corona-forming blocks using the seeded-growth "living" crystallization-driven self-assembly method. The highly ordered crystalline PDHF core in the fibers functions as a donor and permits long-range exciton transport (>200 nm). Energy can therefore be funneled through the fiber core to QDs and QRs that function as acceptor materials and which are noncovalently bound to spatially defined coronal regions of poly(2-vinylpyridine) (P2VP) or quaternized polyfluorene (QPF). Using steady-state and time-resolved spectroscopy, we demonstrate that efficient energy transfer (over 70%) occurs from the crystalline PDHF donor core to the acceptor CdSe QRs attached at the fiber termini. The emission of the PDHF donor in the hybrid conjugate was extensively quenched (by 84%), and a subsequent 4-fold enhancement of the QR emission in solution was observed. These results indicate that the conjugates prepared in this work show promise for potential applications in fields such as light-emitting diodes, photovoltaics, chemical sensors, and photocatalysis.

Patchy Micelles with a Crystalline Core: Self-Assembly Concepts, Properties, and Applications

Crystallization-driven self-assembly (CDSA) of block copolymers bearing one crystallizable block has emerged to be a powerful and highly relevant method for the production of one- and two-dimensional micellar assemblies with controlled length, shape, and corona chemistries. This gives access to a multitude of potential applications, from hierarchical self-assembly to complex superstructures, catalysis, sensing, nanomedicine, nanoelectronics, and surface functionalization. Related to these applications, patchy crystalline-core micelles, with their unique, nanometer-sized, alternating corona segmentation, are highly interesting, as this feature provides striking advantages concerning interfacial activity, functionalization, and confinement effects. Hence, this review aims to provide an overview of the current state of the art with respect to self-assembly concepts, properties, and applications of patchy micelles with crystalline cores formed by CDSA. We have also included a more general discussion on the CDSA process and highlight block-type co-micelles as a special type of patchy micelle, due to similarities of the corona structure if the size of the blocks is well below 100 nm.

Uniform 1D Micelles and Patchy & Block Comicelles via Scalable, One-Step Crystallization-Driven Block Copolymer Self-Assembly

Fiber-like (1D) core-crystalline micelles of uniform length can be obtained in protocols involving multiple steps from block copolymers (BCPs) in which crystallization of the core-forming polymer drives the self-assembly. Here we report a systematic study that shows that adding small amounts (<5 w/w%) of a homopolymer corresponding to the core-forming block of the BCP enables uniform 1D micelles (mean lengths L_n = 0.6 to 9.7 μm) to be obtained in a single step, simply by heating the mixture in a selective solvent followed by slow cooling. A series of poly(ferrocenyldimethylsilane) (PFS) BCPs with different corona-forming blocks and different compositions as well as PFS homopolymers of different lengths were examined. Dye labeling and confocal fluorescence microscopy showed that the homopolymer ends up in the center of the micelle, signaling that it served as the initial seed for epitaxial micelle growth. The rate of unimer addition was strongly enhanced by the length of the PFS block, and this enabled more complex structures to be formed in one-pot self-assembly experiments from mixtures of two or three BCPs with different PFS block lengths. Furthermore, BCP mixtures that included PFS-b-PI (PI = polyisoprene) and PFS-b-PDMS with similar PFS block lengths resulted in simultaneous addition to growing micelles, resulting in a patchy block that could be visualized by staining the vinyl groups of the PI with Pt nanoparticles. This approach also enabled scale up, so that uniform 1D micelles of controlled architecture can be obtained at concentrations of 10 w/w % solids or more.

Robust nucleation control via crisscross polymerization of highly coordinated DNA slats

Natural biomolecular assemblies such as actin filaments or microtubules can exhibit all-or-nothing polymerization in a kinetically controlled fashion. The kinetic barrier to spontaneous nucleation arises in part from positive cooperativity deriving from joint-neighbor capture, where stable capture of incoming monomers requires straddling multiple subunits on a filament end. For programmable DNA self-assembly, it is likewise desirable to suppress spontaneous nucleation to enable powerful capabilities such as all-or-nothing assembly of nanostructures larger than a single DNA origami, ultrasensitive detection, and more robust algorithmic assembly. However, existing DNA assemblies use monomers with low coordination numbers that present an effective kinetic barrier only for slow, near-reversible growth conditions. Here we introduce crisscross polymerization of elongated slat monomers that engage beyond nearest neighbors which sustains the kinetic barrier under conditions that promote fast, irreversible growth. By implementing crisscross slats as single-stranded DNA, we attain strictly seed-initiated nucleation of crisscross ribbons with distinct widths and twists.

Constructing helical nanowires via polymerization-induced self-assembly

While reliable strategies for constructing block copolymer (BCP) nanowires have been developed, helical nanowires are rarely reported in polymerization-induced self-assembly (PISA). Herein, in this work, a new strategy for constructing helical nanowires was developed via PISA mediated by a fluorinated stabilizer block. Ultralong nanowires with helical structure can be readily produced in a wide range of block compositions. In addition, the generality of this strategy was well testified by expanding monomer types. The achiral BCP nano-objects underwent a morphology transition from spheres to helical nanowires during aging. We believe this work will provide a general strategy for producing helical nanowires through PISA of achiral BCPs.

Emerging applications for living crystallization-driven self-assembly

The use of crystallization as a tool to control the self-assembly of polymeric and molecular amphiphiles in solution is attracting growing attention for the creation of non-spherical nanoparticles and more complex, hierarchical assemblies. In particular, the seeded growth method termed living crystallization-driven self-assembly (CDSA) has been established as an ambient temperature and potentially scalable platform for the preparation of low dispersity samples of core-shell fiber-like or platelet micellar nanoparticles. Significantly, this method permits predictable control of size, and access to branched and segmented structures where functionality is spatially-defined. Living CDSA operates under kinetic control and shows many analogies with living chain-growth polymerizations of molecular organic monomers that afford well-defined covalent polymers of controlled length except that it covers a much longer length scale (ca. 20 nm to 10 μm). The method has been applied to a rapidly expanding range of crystallizable polymeric amphiphiles, which includes block copolymers and charge-capped homopolymers, to form assemblies with crystalline cores and solvated coronas. Living CDSA seeded growth methods have also been transposed to a wide variety of π-stacking and hydrogen-bonding molecular species that form supramolecular polymers in processes termed "living supramolecular polymerizations". In this article we outline the main features of the living CDSA method and then survey the promising emerging applications for the resulting nanoparticles in fields such as nanomedicine, colloid stabilization, catalysis, optoelectronics, information storage, and surface functionalization.

RAFT dispersion polymerization of N,N-dimethylacrylamide in a series of n-alkanes using a thermoresponsive poly(tert-octyl acrylamide) steric stabilizer

Poly(tert-octyl acrylamide)-poly(N,N-dimethylacrylamide) nanoparticles are prepared by RAFT dispersion polymerization at 70 °C in various n-alkanes. Thermoreversible flocculation occurs in higher n-alkanes on cooling to 20 °C.

Creation of polymeric nanostructures by living coordination block copolymerization of allene derivatives with fluoroalkyl substituents under polymerization-induced self-assembly conditions and their application to superhydrophobic surfaces

Block copolymer micelles with a fluorous corona were synthesized via living allene polymerization in fluorous media and a polymerization-induced self-assembly (PISA) process, resulting in excellent superhydrophobic optically transparent coatings.

Towards scalable, low dispersity, and dimensionally tunable 2D platelets using living crystallization-driven self-assembly

Scalable low dispersity platelets were accessed through the self-assembly of crystallizable charge-terminated PFS homopolymers. The use of surfactant counteranions, as well as increasing the self-assembly temperature, improved structure fidelity.

Light-directed trapping of metastable intermediates in a self-assembly process

Self-assembly is a dynamic process that often takes place through a stepwise pathway involving formation of kinetically favored metastable intermediates prior to generation of a thermodynamically preferred supramolecular framework. Although trapping intermediates in these pathways can provide significant information about both their nature and the overall self-assembly process, it is a challenging venture without altering temperature, concentrations, chemical compositions and morphologies. Herein, we report a highly efficient and potentially general method for "trapping" metastable intermediates in self-assembly processes that is based on a photopolymerization strategy. By employing a chiral perylene-diimide possessing a diacetylene containing an alkyl chain, we demonstrated that the metastable intermediates, including nanoribbons, nanocoils and nanohelices, can be effectively trapped by using UV promoted polymerization before they form thermodynamic tubular structures. The strategy developed in this study should be applicable to naturally and synthetically abundant alkyl chain containing self-assembling systems.

Ring-opening polymerization-induced crystallization-driven self-assembly of poly-L-lactide-block-polyethylene glycol block copolymers (ROPI-CDSA)

The self-assembly of block copolymers into 1D, 2D and 3D nano- and microstructures is of great interest for a wide range of applications. A key challenge in this field is obtaining independent control over molecular structure and hierarchical structure in all dimensions using scalable one-pot chemistry. Here we report on the ring opening polymerization-induced crystallization-driven self-assembly (ROPI-CDSA) of poly-L-lactide-block-polyethylene glycol block copolymers into 1D, 2D and 3D nanostructures. A key feature of ROPI-CDSA is that the polymerization time is much shorter than the self-assembly relaxation time, resulting in a non-equilibrium self-assembly process. The self-assembly mechanism is analyzed by cryo-transmission electron microscopy, wide-angle x-ray scattering, Fourier transform infrared spectroscopy, and turbidity studies. The analysis revealed that the self-assembly mechanism is dependent on both the polymer molecular structure and concentration. Knowledge of the self-assembly mechanism enabled the kinetic trapping of multiple hierarchical structures from a single block copolymer.

Rapid formation and real-time observation of micron-sized conjugated nanofibers with tunable lengths and widths in 20 minutes by living crystallization-driven self-assembly

Preparing well-defined semiconducting nanostructures from conjugated polymers is of paramount interest for organic optoelectronic devices. Several studies have demonstrated excellent structural and size control from block copolymers (BCPs) containing non-conjugated blocks via crystallization-driven self-assembly (CDSA); however, the precise control of their size and shape remains a challenge due to their poor solubility, causing rapid and uncontrolled aggregation. This study presents a new type of fully conjugated BCP comprising two polyacetylene derivatives termed poly(cyclopentenylene-vinylene) to prepare semiconducting 1D nanofibers. Interestingly, the widths of nanofibers were tuned from 12 to 32 nm based on the contour lengths of their crystalline core blocks. Their lengths could also be controlled from 48 nm to 4.7 μm using the living CDSA. Monitoring of the growth kinetics of the living CDSA revealed the formation of micron-sized 1D nanofibers in less than 20 min. The rapid CDSA enabled us to watch real-time growth using confocal fluorescence microscopy.

New fully conjugated block copolymers formed semiconducting 1D nanofibers with excellent structural and size control. The rapid living CDSA enabled us to watch the real-time video of the whole self-assembly process.

A facile method for generating worm-like micelles with controlled lengths and narrow polydispersity

This work shows that highly uniform worm micelles formed by polymerisation induced self-assembly can be obtained via simple post-synthesis sonication. Importantly, this straightforward and versatile strategy yields exceptionally monodisperse worms with tunable aspect ratios ranging from 7.2 to 17.6 by simply changing the sonication time.

Ethylene Polymerization-Induced Self-Assembly (PISA) of Poly(ethylene oxide)-block-polyethylene Copolymers via RAFT

Poly(ethylene oxide) (PEO) with dithiocarbamate chain ends (PEO-SC(=S)-N(CH₃ )Ph and PEO-SC(=S)-NPh₂ , named PEO-1 and PEO-2, respectively) were used as macromolecular chain-transfer agents (macro-CTAs) to mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization of ethylene in dimethyl carbonate (DMC) under relatively mild conditions (80 °C, 80 bar). While only a slow consumption of PEO-1 was observed, the rapid consumption of PEO-2 led to a clean chain extension and the formation of a polyethylene (PE) segment. Upon polymerization, the resulting block copolymers PEO-b-PE self-assembled into nanometric objects according to a polymerization-induced self-assembly (PISA).

Rod-coil block copolymer aggregates via polymerization-induced self-assembly

Polymerization-induced self-assembly (PISA), incorporating the polymerization with in situ self-assembly, can achieve nano-objects efficiently. However, the cooperative polymerization and self-assembly lead to unclear polymerization kinetics and aggregation behavior, especially for the systems forming rigid chains. Here, we used dissipative particle dynamics simulations with a probability-based reaction model to explore the PISA behavior of rod-coil block copolymer systems. The impact of the length of macromolecular initiators, the targeted length of rigid chains, and the reaction probability on the PISA behavior, including polymerization kinetics and self-assembly, were examined. The difference between PISA and traditional self-assembly was revealed. A comparison with experimental observations shows that the simulation can capture the essential feature of the PISA. The present work provides a comprehensive understanding of rod-coil PISA systems and may provide meaningful information for future experimental research.

Antimicrobial Honey-Inspired Glucose-Responsive Nanoreactors by Polymerization-Induced Self-Assembly

The rise of antimicrobial resistance is at the forefront of global healthcare challenges, with antimicrobial infections on track to overtake cancer as a leading cause of death by 2050. The high effectiveness of antimicrobial enzymes used in combination with the protective, inert nature of polymer materials represents a highly novel approach toward tackling microbial infections. Herein, we have developed biohybrid glucose oxidase-loaded semipermeable polymersome nanoreactors, formed using polymerization-induced self-assembly, and demonstrate for the first time their ability to "switch on" their antimicrobial activity in response to glucose, a ubiquitous environmental stimulus. Using colony-counting assays, it was demonstrated that the nanoreactors facilitate up to a seven-log reduction in bacterial growth at high glucose concentrations against a range of Gram-negative and Gram-positive bacterial pathogens, including a methicillin-resistant Staphylococcus aureus clinical isolate. After demonstrating the antimicrobial properties of these materials, their toxicity against human fibroblasts was assessed and the dosage of the nanoreactors further optimized for use as nontoxic agents against Gram-positive bacteria under physiological blood glucose concentrations. It is envisaged that such biohybrid nanomaterials will become an important new class of antimicrobial biomaterials for the treatment of bacterial infections.

One-Pot Synthesis of Cross-linked Block Copolymer Nanowires via Polymerization-Induced Hierarchical Self-Assembly and Photodimerization

Block copolymer (BCP) nanowires are crucially important in diversified fields. However, their applications typically suffer from a tedious fabrication process, heterogeneous morphology, and degradation. Herein, we propose a facile and robust approach to synthesize stilbene-containing BCP nanowires in homogeneous morphology with high stability at high solid content (5%-20% w/w) in one pot. It is realized by the polymerization-induced hierarchical self-assembly and subsequent photodimerization cross-linking under UV irradiation of stilbene mesogens in the core-forming block in the later stage of polymerization. Because of the strong liquid crystalline ordering and photodimerization of stilbene, the cross-linked nanowires can be obtained over a broad BCP composition, which show robust morphological stability when exposed to solvent dissolution tests and water dispersion stability tests. This efficient approach to stabilized nanowires with homogeneous morphology via in situ cross-linking would be useful in various fields, such as nanomedicine and Pickering emulsifiers.

Remote Perfluoroalkyl Substituents are Key to Living Aqueous Ethylene Polymerization

In various nickel(II) salicylaldiminato ethylene polymerization catalysts, which are a versatile mechanistic probe for substituent effects, longer perfluoroalkyl groups exert a strong effect on catalytic activities and polymer microstructures compared to the trifluoromethyl group. This effect is accounted for by a reduced electron density on the active sites, and is also supported by electrochemical studies. Thus, β‐hydride elimination, the key step of chain transfer and branching pathways, is disfavored while chain‐growth rates are enhanced. This enhancement occurs to an extent that enables living polymerizations in aqueous systems to afford ultra‐high‐molecular‐weight polyethylene for various chelating salicylaldimine motifs. These findings are mechanistically instructive as well as practically useful for illustrating the potential of perfluoroalkyl groups in catalyst design.

Unique aqueous self-assembly behavior of a thermoresponsive diblock copolymer

It is well-recognized that block copolymer self-assembly in solution typically produces spheres, worms or vesicles, with the relative volume fraction of each block dictating the copolymer morphology. Stimulus-responsive diblock copolymers that can undergo either sphere/worm or vesicle/worm transitions are also well-documented. Herein we report a new amphiphilic diblock copolymer that can form spheres, worms, vesicles or lamellae in aqueous solution. Such self-assembly behavior is unprecedented for a single diblock copolymer of fixed composition yet is achieved simply by raising the solution temperature from 1 °C (spheres) to 25 °C (worms) to 50 °C (vesicles) to 70 °C (lamellae). Heating increases the degree of hydration (and hence the effective volume fraction) of the core-forming block, with this parameter being solely responsible for driving the sphere-to-worm, worm-to-vesicle and vesicle-to-lamellae transitions. The first two transitions exhibit excellent reversibility but the vesicle-to-lamellae transition exhibits hysteresis on cooling. This new thermoresponsive diblock copolymer provides a useful model for studying such morphological transitions and is likely to be of significant interest for theoretical studies.

A polymerization-induced self-assembly process for all-styrenic nano-objects using the living anionic polymerization mechanism

By combination of the living anionic polymerization (LAP) mechanism with the polymerization-induced self-assembly (PISA) technique, the all-styrenic diblock copolymer poly(p-tert-butylstyrene)-b-polystyrene (PtBS-b-PS) based LAP PISA was successfully developed.

Scalable preparation of crystalline nanorods through sequential polymerization-induced and crystallization-driven self-assembly of alternating copolymers

We report a two-step sequential polymerization-induced and crystallization-driven self-assembly (sequential PI/CDSA) of alternating copolymers to prepare micron-length crystalline nanorods with an ultrathin lamellar structure on a large scale.

Facile preparation of one-dimensional nanostructures through polymerization-induced self-assembly mediated by host–guest interaction

A RAFT aqueous dispersion polymerization of ferrocenylmethyl acrylate mediated by host–guest interaction was investigated and a series of peculiar one-dimensional morphologies can be readily obtained.

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.

Polymerization-induced self-assembly for the fabrication of polymeric nano-objects with enhanced structural stability by cross-linking

This review discusses the strategies of core-cross-linking in most of the PISA literatures (including post-polymerization cross-linking, photo-cross-linking and in situ cross-linking) and the applications of the cross-linked nano-objects.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

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.

ROMPI-CDSA: ring-opening metathesis polymerization-induced crystallization-driven self-assembly of metallo-block copolymers

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) are among the most prevailing methods for block copolymer self-assembly. Taking the merits of scalability of PISA and dimension control of CDSA, we report one-pot synchronous PISA and CDSA via ring-opening metathesis polymerization (ROMP) to prepare nano-objects based on a crystalline poly(ruthenocene) motif. We denote this self-assembly methodology as ROMPI-CDSA to enable a simple, yet robust approach for the preparation of functional nanomaterials.

Efficient occlusion of oil droplets within calcite crystals

It is well known that oil and water do not mix. Similarly, the incorporation of oil droplets within inorganic crystals is highly counter-intuitive because there is a large difference in surface energy for these two components. Nevertheless, herein we demonstrate the efficient occlusion of ∼250-500 nm oil droplets within 20-40 μm calcite crystals. These droplets are stabilized using various amphiphilic poly(methacrylic acid)-poly(n-alkyl methacrylate) diblock copolymer emulsifiers. Both copolymer concentration and diblock compositions affect the extent of occlusion, with optimized conditions producing calcite crystals containing up to 11% oil by mass. Moreover, compressive forces exerted by the growing crystals cause significant deformation of the oil droplets during occlusion. In principle, this protocol enables the incorporation of water-insoluble dyes or hydrophobic nanoparticles within calcite, which is a cheap, naturally-occurring and environmentally-benign mineral. The single crystal nature of this host lattice ensures efficient retention of such guests, while lowering the solution pH leads to triggered release via acid dissolution.

Organobase triggered controlled supramolecular ring opening polymerization and 2D assembly

A carboxylic acid appended naphthalene-diimide (NDI) derivative spontaneously aggregates in decane to generate a kinetically controlled product with irregular fibrillar morphology. By fine-tuning the sample preparation conditions, the carboxylic acid group can be trapped by intra-molecular H-bonds with the adjacent imide carbonyl, which retards the spontaneous aggregation. In the presence of a catalytic amount of a non-nucleophilic organic base (DBU or DMAP), the meta-stable monomer exhibits supramolecular polymerization through a thermodynamically controlled pathway involving simultaneous H-bonding and π-stacking and generates ultra-thin 2D nano-sheets. DMAP/DBU helps in ring-opening of the intra-molecularly H-bonded monomer and in situ breeds the free acid, which, beyond a critical concentration, initiates controlled supramolecular ring opening polymerization (SROP) via the chain-growth mechanism. The 2D polymer acts as a macro-initiator for subsequent two cycles of SROP and produces laterally extended ultra-thin nano-sheets.