Influence of Spacer Lengths on the Morphology of Biphenyl-Containing Liquid Crystalline Block Copolymer Nanoparticles via Polymerization-Induced Self-Assembly

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.

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.

Recent Progress in Azobenzene-Based Supramolecular Materials and Applications

Azobenzene-containing small molecules and polymers are functional photoswitchable molecules to form supramolecular nanomaterials for various applications. Recently, supramolecular nanomaterials have received enormous attention in material science because of their simple bottom-up synthesis approach, understandable mechanisms and structural features, and batch-to-batch reproducibility. Azobenzene is a light-responsive functional moiety in the molecular design of small molecules and polymers and is used to switch the photophysical properties of supramolecular nanomaterials. Herein, we review the latest literature on supramolecular nano- and micro-materials formed from azobenzene-containing small molecules and polymers through the combinatorial effect of weak molecular interactions. Different classes including complex coacervates, host-guest systems, co-assembled, and self-assembled supramolecular materials, where azobenzene is an essential moiety in small molecules, and photophysical properties are discussed. Afterward, azobenzene-containing polymers-based supramolecular photoresponsive materials formed through the host-guest approach, polymerization-induced self-assembly, and post-polymerization assembly techniques are highlighted. In addition to this, the applications of photoswitchable supramolecular materials in pH sensing, and CO2 capture are presented. In the end, the conclusion and future perspective of azobenzene-based supramolecular materials for molecular assembly design, and applications are given.

Seeded RAFT Polymerization-Induced Self-assembly: Recent Advances and Future Opportunities

Over the past decade, polymerization-induced self-assembly (PISA) has fully proved its versatility for scale-up production of block copolymer nanoparticles with tunable sizes and morphologies; yet, there are still some limitations. Recently, seeded PISA approaches combing PISA with heterogeneous seeded polymerizations have been greatly explored and are expected to overcome the limitations of traditional PISA. In this review, recent advances in seeded PISA that have expanded new horizons for PISA are highlighted including i) general considerations for seeded PISA (e.g., kinetics, the preparation of seeds, the selection of monomers), ii) morphological evolution induced by seeded PISA (e.g., from corona-shell-core nanoparticles to vesicles, vesicles-to-toroid, disassembly of vesicles into nanospheres), and iii) various well-defined nanoparticles with hierarchical and sophisticated morphologies (e.g., multicompartment micelles, porous vesicles, framboidal vesicles, AXn -type colloidal molecules). Finally, new insights into seeded PISA and future perspectives are proposed.

RAFT polymerization-induced self-assembly of semifluorinated liquid-crystalline block copolymers

It is a major challenge to prepare commercially viable scale semifluorinated liquid-crystalline block copolymers (SEFL-BCPs) using solution processing techniques. The technology of selectively solvating one block in a suitable solvent to realize self-assembly provides a promising route for the preparation of core-corona block polymer materials with extensive potential applications. However, considerable limitations have been discovered after much practice. BCP assemblies often require a separate synthesis step and are performed at high dilution. Herein, a one-pot approach combining polymerization-induced and crystallization-driven self-assembly (PISA-CDSA) was used to obtain well-defined, precise compositions of SEFL-BCPs. It is first synthesized via reversible addition-fragmentation chain transfer ethanol dispersion polymerization between 1H,1H,2H,2H-heptadecafluorodecyl acrylate and poly(N,N-dimethylacrylamide) at a concentration up to 20% v/v. Various morphologies, including 1D fiber-like micelles, 2D lamellar structures, and fusion structures, were first observed via transmission electron microscopy. This scalable PISA-CDSA strategy is greatly expanding the morphology scope and applicability of the polymer liquid crystal materials science field.

Steroid-Based Liquid Crystalline Polymers: Responsive and Biocompatible Materials of the Future

Steroid-based liquid crystal polymers and co-polymers have come a long way, with new and significant advances being made every year. This paper reviews some of the recent key developments in steroid-based liquid crystal polymers and co-polymers. It covers the structure–property relationship between cholesterol and sterol-based compounds and their corresponding polymers, and the influence of chemical structure and synthesis conditions on the liquid crystalline behaviour. An overview of the nature of self-assembly of these materials in solvents and through polymerisation is given. The role of liquid crystalline properties in the applications of these materials, in the creation of nano-objects, drug delivery and biomedicine and photonic and electronic devices, is discussed.

Investigation of Thermal-Induced Changes in Molecular Order on Photopolymerization and Performance Properties of a Nematic Liquid-Crystal Diacrylate

Polymerization shrinkage and associated stresses are the main reasons for dental restorative failure. We developed a series of liquid crystal diacrylates and dimethacrylates which have markedly low polymerization shrinkage. In order to fully understand the effects of temperature-induced changes of molecular order on the photopolymerization process and performance properties of the generated polymers, the photopolymerization of a difunctional acrylate, 2-t-butyl-1,4-phenylene bis (4-(6-(acryloyloxy)hexyloxy)benzoate), which exists in the nematic liquid crystalline phase at room temperature, was investigated as a function of photopolymerization temperature over the nematic to isotropic range. Morphological studies suggested that a mesogenic phase was immediately formed in the polymer even if polymerization in thin films occurred above the nematic-to-isotropic (N→I) transition temperature of the monomer (Tn-i = 45.8 °C). Dynamic mechanical analysis of 2 × 2 mm cross-section bar samples polymerized at 60 °C showed reduced elastic moduli, increased glass transition temperature and formation of a more crosslinked network, in comparison to polymers formed at lower polymerization temperatures. Fractography analysis showed that polymers generated from the nematic liquid crystalline phase underwent a different fracture pattern in comparison to those generated from the isotropic phase. Volumetric shrinkage (2.2%) found in polymer polymerized from the nematic liquid crystalline phase at room temperature was substantially less than the 6.0% observed in polymer polymerized from an initial isotropic phase at 60 °C, indicating that an organized monomer can greatly contribute to reducing cure shrinkage.

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.

Self-Assembly of Copolymers Containing Crystallizable Blocks: Strategies and Applications

The self-assembly of copolymers containing crystallizable block in solution has received increasing attentions in the past few years. Various strategies including crystallization-driven self-assembly (CDSA) and polymerization-induced CDSA (PI-CDSA) have been widely developed. Abundant self-assembly morphologies were captured and advanced applications have been attempted. In this review, the synthetic strategies including the mechanisms and characteristics are highlighted, the survey on the advanced applications of crystalline nano-assemblies are collected. This review is hoped to depict a comprehensive outline for self-assembly of copolymers containing crystallizable block in recent years and to prompt the development of the self-assembly technology in interdisciplinary field. This article is protected by copyright. All rights reserved.

Synthesis of Cross-Linked Block Copolymer Nano-Assemblies and their Coating Application

Since the discovery of polymerization-induced self-assembly (PISA), convenient synthesis of concentrated block copolymer nano-assemblies dispersed in solvent has been achieved. Now, application of block copolymer nano-assemblies should be paid more attention. In this study, corona-cross-linked block copolymer nanoparticles of poly[dimethylacrylamide-co-(diacetone acrylamide)]-b-polystyrene [P(DMA-co-DAAM)-b-PS] containing the poly(DAAM) segment in the hydrophilic P(DMA-co-DAAM) block are synthesized initially by PISA following dispersion RAFT polymerization and then by covalent intraparticle cross-linking through the poly(DAAM) segment and adipic acid dihydrazide (ADH). Coating application of the corona-cross-linked block copolymer nano-assemblies is tried, and much higher water resistance of the corona-cross-linked block copolymer nano-assemblies than that of the linear block copolymer nano-assemblies is demonstrated. This article is protected by copyright. All rights reserved.

Building Permanently Optically Active Particles from Absolutely Achiral Polymer

Chirality in polymer particles represents one of the most dynamic areas of nanoscale materials today. The chirality of most chiral polymeric particles (CPPs) derived from achiral monomers/polymers has a strong...

Polymers with multiple functions: α,ω-macromolecular photoinitiators/chain transfer agents used in aqueous photoinitiated polymerization-induced self-assembly

A series of α,ω-functionalized polymers with a photoinitiator end group and a RAFT end group were synthesized and employed as macromolecular photoinitiators/chain transfer agents in aqueous photoinitiated polymerization-induced self-assembly.

Organic–inorganic hybrid nanomaterials prepared via polymerization-induced self-assembly: recent developments and future opportunities

This review highlights recent developments in the preparation of organic–inorganic hybrid nanomaterials via polymerization-induced self-assembly.

A polymerization-induced gelation process visualized by nontraditional clustering-triggered emission

A kind of organogel with distinct CTE properties was synthesized via a PISA process. Fluorescence variation could be employed to realize the visualization of the PISA process according to the CTE mechanism.

Controlling the Multiple Chiroptical Inversion in Biphasic Liquid-Crystalline Polymers

While controlling the chirality and modulating the helicity is a challenging task, it attracts great research interest for gaining a better understanding of the origin of chirality in nature. Herein, structurally similar azobenzene (Azo) vinyl monomers were designed in which the alkyl chains comprised the chiral stereocenter with different achiral tail lengths. Combining the synchronous polymerization, supramolecular stacking and self-assembly, the multiple chiroptical inversion of the Azo-polymer supramolecular assemblies can be modulated by the tail length and DP of Azo blocks during in situ polymerization. The DP-, UV light-, temperature-, aging time-dependent chiroptical properties and liquid-crystalline (LC) characterization indicated that the amorphous-to-LC phase transition and biphasic LC interconversion allow the transcription of intra-chain π-π stacking, inter-chain H- and J-aggregation, thereby controlling the dynamic multiple reversal of supramolecular chirality.

Polymerization-Induced Helicity Inversion Driven by Stacking Modes and Self-Assembly Pathway Differentiation

Regulating the mutual stacking arrangements is of great interest for understanding the origin of chirality at different hierarchical levels in nature. Different from molecular level chirality, the control and manipulation of hierarchical chirality in polymer systems is limited to the use of external factors as the energetically demanding switching stimulus. Herein, the first self-assembly strategy of polymerization-induced helicity inversion (PIHI), in which the controlled packing and dynamic stereomutation of azobenzene (Azo) building blocks are realized by in situ polymerization without any external stimulus, is reported. A multiple helicity inversion and intriguing helix-helix transition of polymeric supramolecular nanofibers occurs during polymerization, which is collectively confirmed to be mediated by the transition between functionality-oriented π-π stacking, H-, and J-aggregation. The studies further reveal that helicity inversion proceeds through a delicate interplay of the thermodynamically and kinetically controlled, pathway-dependent interconversion process, which should provide new insight into the origin and handedness control of helical nanostructures with desired chirality.

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.

Inverse Bicontinuous Structure by Polymerization-Induced Self-Assembly Against Single-Chain Nanoparticles

Polymer particles with inverse bicontinuous structures have attracted considerable attention due to their diverse applications. The conventional generation requires controlling numerous key parameters under strict conditions, such as solvent property, polymer composition, and architecture. In order to improve the preparation efficiency within a broad window, we employed a method by polymerization-induced self-assembly (PISA) against intramolecularly folded single-chain nanoparticles (SCNPs). The SCNPs bear an active site for further polymerization. The SCNPs with smaller sizes facilitate easier controlling of the packing parameter above unity to meet the requirement of the unique structures. The concept is demonstrated by forming the inverse bicontinuous structure through PISA in ethanol against two SCNPs of P4VP(SCNP_x%)₃₅-CTA and P(PEGMA₂₀-co-TMSPMA₄)(SCNP_16.7%)-CTA. The unique structure is easily achieved when growing a relatively shorter polymer chain within a broad window. The work paves the avenue to prepare polymer particles with the unique structure in large scale, and other functional materials are expected by using the functional SCNPs or favorable growth of desired materials within the particles.

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.

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.

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).