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

Mesogenic Ordering-Driven Self-Assembly of Liquid Crystalline Block Copolymers in Solution

With the development of nanotechnology, the preparation of polymeric nanoparticles with nicely defined structures has been well-developed, and the functionalization and subsequent applications of the resultant nanostructures are becoming increasingly important. Particularly, by introducing mesogenic ordering as the driving force for the solution-state self-assembly of liquid crystalline (LC) block copolymers (BCPs), micellar nanostructures with different morphologies, especially anisotropic morphologies, can be easily prepared. This review summarizes the recent progress in the solution-state self-assembly of LC BCPs and is mostly focused on four main related aspects, including an in-depth understanding of the mesogenic ordering-driven self-assembly, precise assembly methods, utilization of these methods to fabricate hierarchical structures, and the potential applications of these well-defined nanostructures. We hope not only to make a systematic summary of previous studies but also to provide some useful thinking for the future development of this field.

Modern Trends in Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Degradable Block Copolymer Nanoparticles Synthesized by Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) combines polymerization and in situ self-assembly of block copolymers in one system and has become a widely used method to prepare block copolymer nanoparticles at high concentrations. The persistence of polymers in the environment poses a huge threat to the ecosystem and represents a significant waste of resources. There is an urgent need to develop novel chemical approaches to synthesize degradable polymers. To meet with this demand, it is crucial to install degradability into PISA nanoparticles. Most recently, degradable PISA nanoparticles have been synthesized by introducing degradation mechanisms into either shell-forming or core-forming blocks. This Minireview summarizes the development in degradable block copolymer nanoparticles synthesized by PISA, including shell-degradable, core-degradable, and all-degradable nanoparticles. Future development will benefit from expansion of polymerization techniques with new degradation mechanisms and adaptation of high-throughput approaches for both PISA syntheses and degradation studies.

Liquid Crystalline Nanoparticles via Polymerization-Induced Self-Assembly: Morphology Evolution and Function Regulation

Liquid crystalline nanoparticles (LC NPs) are a kind of polymer NPs with LC mesogens, which can form special anisotropic morphologies due to the influence of LC ordering. Owing to the stimuli-responsiveness of the LC blocks, LC NPs show abundant morphology evolution behaviors in response to external regulation. LC NPs have great application potential in nano-devices, drug delivery, special fibers and other fields. Polymerization-induced self-assembly (PISA) method can synthesize LC NPs at high solid content, reducing the harsh demand for reaction solvent of the LC polymers, being a better choice for large-scale production. In this review, we introduced recent research progress of PISA-LC NPs by dividing them into several parts according to the LC mesogen, and discussed the improvement of experimental conditions and the potential application of these polymers.

Azobenzene-Containing Liquid Crystalline Twisted Ribbons via Polymerization-Induced Hierarchical Self-Assembly

Polymerization-induced self-assembly incorporating liquid crystallization, as a polymerization-induced hierarchical self-assembly (PIHSA) method to produce polymeric particles with anisotropic morphologies facilely and efficiently, has drawn wide attention recently. However, the means of regulating the morphologies of liquid crystalline (LC) polymer assemblies still need to be explored. Herein, a route is presented to fabricate the twisted ribbons via PIHSA containing azobenzene based on poor reversible addition-fragmentation chain transfer (RAFT) control, called poorly controlled PIHSA. Cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid-2-(2-pyridyldithio) ethyl ester is used as the RAFT agent with poor controllability, and the morphological evolution from ribbons to twisted ribbons can be observed in the corresponding PIHSA system. The formation mechanism of the twisted ribbons is studied systematically and the broad molecular weight distribution is considered to be the decisive factor. Moreover, the supramolecular chirality induced by symmetry breaking is also related to the twist of the ribbons. This study enriches the methods of controlling the morphologies of LC polymer particles and is helpful for further clarifying the mechanism of PIHSA.

Gaining Structural Control by Modification of Polymerization Rate in Ring-Opening Polymerization-Induced Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) has become an important one pot method for the preparation of well-defined block copolymer nanoparticles. In PISA, morphology is typically controlled by changing molecular architecture and polymer concentration. However, several computational and experimental studies have suggested that changes in polymerization rate can lead to morphological differences. Here, we demonstrate that catalyst selection can be used to control morphology independent of polymer structure and concentration in ring-opening polymerization-induced crystallization-driven self-assembly (ROPI-CDSA). Slower rates of polymerization give rise to slower rates of self-assembly, resulting in denser lamellae and more 3D structures when compared to faster rates of polymerization. Our explanation for this is that the fast samples transiently exist in a nonequilibrium state as self-assembly starts at a higher solvophobic block length when compared to the slow polymerization. We expect that subsequent examples of rate variation in PISA will allow for greater control over morphological outcome.

In situ generation and evolution of polymer toroids by liquid crystallization-assisted seeded dispersion polymerization

An effective method is presented for preparing high solid content azobenzene-containing triblock copolymer toroidal assemblies by liquid crystallization-assisted seeded dispersion polymerization. Vesicles are prepared via polymerization-induced self-assembly (PISA), and used as seeds for further chain extension. By introducing smectic liquid crystalline (LC) ordering into the core-forming block, toroids are formed in situ during the polymerization. The morphological transformation from toroids to barrels is observed under ultraviolet irradiation due to the photo-isomerization of the azobenzene mesogens. This strategy expands the scope of tunable anisotropic morphologies for potential functional nanomaterials based on a LC copolymer by seeded dispersion polymerization.

Highly photosensitive furan acrylate derivatives and their solid-state photopolymerization

Highly photosensitive multifunctional furan acrylate monomers synthesized from biomass furfural can be photopolymerized into polyesters without photoinitiators and solvents.

Polyether-Based Diblock Terpolymer Micelles with Pendant Anthracene Units-Light-Induced Crosslinking and Limitations Regarding Reversibility

The synthesis of 9-methylanthracenyl glycidyl ether (AnthGE) as a crosslinkable monomer that can be applied in anionic ring opening polymerization is reported. Diblock terpolymers of the composition methoxy-poly(ethylene oxide)-block-poly(2-ethylhexyl glycidyl ether-co-9-methylanthracenyl glycidyl ether) (mPEO-b-P(EHGE-co-AnthGE) with 10 to 24 wt% of AnthGE are synthesized and characterized. Their micellization behavior, as well as their light-induced core-crosslinking via irradiation with UV light (λ = 365 nm) is studied. The results are compared with studies on the dimerization, and the dimer cleavage via irradiation with UV-C light (λ = 254 nm), of the same diblock terpolymer in organic solution, and the small-molecule model compound 9-methoxymethylanthracene. Differences in ¹ H NMR spectra of the crosslinked or dimerized compounds and reaction kinetics of the dimerization reactions under different conditions suggest possible side reactions for the case of the core-crosslinking of micelles in aqueous solution. These side reactions limit the reversibility of the anthracene dimerization reaction in aqueous solutions, even if the anthracene molecule is encapsulated within the hydrophobic core of a polymeric micelle.

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.

Advances, Challenges, and Opportunities of Poly(γ-butyrolactone)-Based Recyclable Polymers

The discovery and prosperous growth of synthetic polymers have presented both significant advantages and daunting challenges in the last century. To address the issues of environmental pollution and fossil consumption, recyclable, degradable, and/or biobased polymers have been given much attention in the polymer science community. This viewpoint focuses on the emerging fully chemical recyclable poly(γ-butyrolactone)-based polymers. The breakthrough from nonpolymerizable to efficient polymerization is highlighted by the benefits of the development of a series of catalysis for ring-opening polymerization of γ-butyrolactone. Subsequently, the design of γ-butyrolactone derivatives and synthesis of more recyclable polymers are summarized together with the discussions about the structure and property relationship. Finally, the remaining challenges and promising opportunities are suggested in order to provide insights into the further direction for sustainable polymers.

Multiswitchable photoacid-hydroxyflavylium-polyelectrolyte nano-assemblies

Light- and pH-responsive nano-assemblies with switchable size and structure are formed by the association of a photoacid, anthocyanidin, and a linear polyelectrolyte in aqueous solution. Specifically, anionic disulfonated naphthol derivatives, neutral hydroxyflavylium, and cationic poly(allylamine) are used as building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to alter the ternary system through external triggering are accessible. The structure and trigger effects can be controlled through the component ratios of the samples. Dynamic and static light scattering (DLS, SLS) and ζ-potential measurements were applied to study the size and the stability of the particles, and information on the molecular structure was gained by UV-vis spectroscopy. Isothermal titration calorimetry (ITC) provided information on the thermodynamics and interaction forces in the supramolecular assembly formation.

Directional effect on the fusion of ellipsoidal morphologies into nanorods and nanotubes

Particle fusion is well-recognized as an important spontaneous process to produce higher-order nanostructures during morphology transition in polymerization-induced self-assembly (PISA). However, to our knowledge, the directional contact, adhesion, and fusion of adjacent nanoparticles have been rarely elucidated in PISA. Herein, a directional fusion of ellipsoidal morphologies was demonstrated during PISA of semi-fluorinated liquid-crystalline (SFLC) block copolymers. The ellipsoidal nanostructures, including micelles and vesicles, preferred to undergo a directional fusion in a head-to-head model, leading to the formation of nanorods and nanotubes, respectively. We believe the directional fusion will offer insightful guidance in PISA to the preparation of complicated functional nanostructures.

In situ cross-linking polymerization-induced self-assembly not only generates cross-linked structures but also promotes morphology transition by the cross-linker

Not only cross-linked structures but also a promoting effect on morphology transition has been observed during the in situ cross-linking PISA by RAFT dispersion copolymerization of 2-(diisopropylamino)ethyl methacrylate and cystaminebismethacrylamide.

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.

The self-assembly of single chain Janus nanoparticles from azobenzene-containing block copolymers and reversible photoinduced morphology transitions

Azobenzene-containing liquid crystalline single chain Janus nanoparticles (LC-SCJNPs) were employed as building blocks to construct assemblies showing a reversible photoinduced morphology transition.

Ionic polyacetylene with a unique nanostructure and high stability by metathesis cyclopolymerization-induced self-assembly

Conjugated ionic polyacetylene was synthesized by metathesis cyclopolymerization, and self-assembled into various nanostructures, which exhibited high thermal and oxidative stability.

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.

Synthesis of azobenzene-containing liquid crystalline block copolymer nanoparticles via polymerization induced hierarchical self-assembly

A facile synthesis of non-spherical photoresponsive azobenzene-containing liquid crystalline nanoparticles via polymerization-induced hierarchical self-assembly (PIHSA).

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-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.