The Self‐Assembled Structure of the Diblock Copolymer PCL‐b‐P4VP Transforms Upon Competitive Interactions with Octaphenol Polyhedral Oligomeric Silsesquioxane

This paper describes the miscibility and self‐assembly, mediated by hydrogen‐bonding interactions, of new block copolymer/nanoparticle blends. The morphologies adopted by the immiscible poly[(ε‐caprolactone)‐block‐(4‐vinyl pyridine)] (PCL‐b‐P4VP) diblock copolymer changes upon increasing the number of competitive hydrogen‐bonding interactions after adding increasing amounts of octaphenol polyhedral oligomeric silsesquioxane (OP‐POSS). Transmission electron microscopy reveals morphologies that exhibit high degrees of long‐range order, such as cylindrical and spherical structures, at relatively low OP‐POSS contents, and short‐range order or disordered structures at higher OP‐POSS contents. Analyses performed using differential scanning calorimetry, wide‐angle X‐ray diffraction, and FT‐IR spectroscopy provide positive evidence that the pyridyl units of the P4VP block are significantly stronger hydrogen‐bond acceptors toward the OH group of OP‐POSS than are the CO groups of the PCL block, thereby resulting in excluded and confined PCL phases.

     

Self‐Assembly of Diblock Copolymers into Novel Snowflake‐Shaped Aggregates Driven by Quadruple Hydrogen Bonding

Two well‐defined diblock copolymers with quadruple hydrogen‐bonding groups on one block, denoted PSUEA‐1 and PSUEA‐2 , have been synthesized, and novel snowflake‐shaped nanometer‐scale aggregates, self‐assembled by such diblock copolymers in non‐polar solvents, have been observed. The micellar dimensions were investigated by DLLS and SLLS. Their morphologies were studied by TEM. Since the degrees of polymerization of the Upy‐containing blocks of PSUEA‐1 and PSUEA‐2 are quite similar and the polystyrene block of the PSUEA‐1 is longer than that of the PSUEA‐2 , a subtle but identifiable difference between the sizes and structures of the PSUEA‐1 and PSUEA‐2 aggregates was noticed and characterized.

     

A Supramolecularly Assisted Transformation of Block‐Copolymer Micelles into Nanotubes

Once around the block : Incorporation of a rigid hydrogen‐bonding benzamide unit, placed at the interface between two polymer blocks, in poly(ethylene glycol) (PEG)–(thio)urea–poly(L ‐lactide) (PLLA) block copolymers transforms the morphology of the block copolymers, from spherical micelles, as formed by PEG‐PLLA diblock copolymers, into nanotubes in solution.

     

Amphiphilic Block‐Graft Copolymers with a Degradable Backbone and Polyethylene Glycol Pendant Chains Prepared via Ring‐Opening Polymerization of a Macromonomer

Well‐defined amphiphilic block‐graft copolymers PCL‐b‐[DTC‐co‐(MTC‐mPEG)] with polyethylene glycol methyl ether pendant chains were designed and synthesized. First, monohydroxyl‐terminated macroinitiators PCL‐OH were prepared. Then, ring‐opening copolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and cyclic carbonate‐terminated PEG (MTC‐mPEG) macromonomer was carried out in the presence of the macroinitiator in bulk to give the target copolymers. All the polymers were characterized by ¹H NMR and gel permeation chromatography (GPC). The polymers have unimodal molecular weight distributions and moderate polydispersity indexes. The amphiphilic block‐graft copolymers self‐assemble in water forming stable micelle solutions with a narrow size distribution.

     

A Signal‐Passing DNA‐Strand‐Exchange Mechanism for Active Self‐Assembly of DNA Nanostructures

DNA nanostructured tiles play an active role in their own self‐assembly in the system described herein whereby they initiate a binding event that produces a cascading assembly process. We present DNA tiles that have a simple but powerful property: they respond to a binding event at one end of the tile by passing a signal across the tile to activate a binding site at the other end. This action allows sequential, virtually irreversible self‐assembly of tiles and enables local communication during the self‐assembly process. This localized signal‐passing mechanism provides a new element of control for autonomous self‐assembly of DNA nanostructures.     

Hydrogen Bonding‐Induced Transformation of Network Aggregates into Vesicles ‐ A Potential Method for the Preparation of Composite Vesicles

While network‐like assemblies are formed by amphiphilic polyphosphazenes with poly(N‐isopropylacrylamide) and ethyl tryptophan as side groups in aqueous solution, a significant morphology transformation is observed when small molecules that exhibit hydrogen‐bonding interactions with amphiphilic copolymers are introduced during the preparation of polymeric assemblies through a dialysis procedure. Depending on copolymer composition and the content of small molecules introduced, aggregates ranging from general vesicles, high‐genus vesicles, to well‐defined nanospheres can be prepared successfully as clearly evidenced by TEM observation, which suggests this procedure should be a novel approach to prepare composite vesicles.

     

Preparation of polyhedral oligomeric silsesquioxane‐containing block copolymer with well‐controlled stereoregularity

Preparation of functional domains with a spacing of 10 nm is a benchmark set to fabricate next‐generation electronic devices. Organic–inorganic block copolymers form well‐ordered microphase separations with very small domain sizes. The design and preparation of a novel block copolymer consisting of syndiotactic polymethyl methacrylate (st‐PMMA) and polyhedral oligomeric silsesquioxane (POSS)‐functionalized polymethacrylate, designated as st‐PMMA‐b‐PMAPOSS, which can recognize functional molecules, are reported. The st‐PMMA segments form a helical structure and encapsulate C₆₀ in the helical nanocavity, leading to the formation of an inclusion complex. Although the ordering of the domains is not high, C₆₀ domains that are in a quasi‐equilibrium state, with about 10‐nm domain spacings, are generated using st‐PMMA‐b‐PMAPOSS that can recognize functional molecules. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2181–2189     

Self‐Assembly in Water of Poly(acrylic acid)‐Based Diblock Copolymers Synthesized by Nitroxide‐Mediated Polymerization

Summary: Amphiphilic diblock copolymers consisting of a hydrophilic block, poly(acrylic acid), and a hydrophobic block, polystyrene, were synthesized by direct nitroxide‐mediated polymerization using the PS block as a macro‐initiator for the first time. Several techniques were used to characterize the amphiphilic block copolymers (size exclusion chromatography, NMR spectroscopy). The proposed method can lead to samples with a broad range of composition and molar mass. Preliminary studies of their self‐assembly in aqueous medium using fluorescence spectroscopy and small‐angle neutron scattering are presented.

Schematic of the formation of the PS‐b‐PAA block copolymers and their micellization in aqueous media.     

Self‐assembly of block copolymers with an alkoxysilane‐based core‐forming block: A comparison of synthetic approaches

Polymerization‐induced self‐assembly (PISA) has become the preferred method of preparing self‐assembled nano‐objects based on amphiphilic block copolymers. The PISA methodology has also been extended to the realization of colloidal nanocomposites, such as polymer–silica hybrid particles. In this work, we compare two methods to prepare nanoparticles based on self‐assembly of block copolymers bearing a core‐forming block with a reactive alkoxysilane moiety (3‐(trimethoxysilyl)propyl methacrylate, MPS), namely (i) RAFT emulsion polymerization using a hydrophilic macroRAFT agent and (ii) solution‐phase self‐assembly upon slow addition of a selective solvent. Emulsion polymerization under both ab initio and seeded conditions were studied, as well the use of different initiating systems. Effective and reproducible chain extension (and hence PISA) of MPS via thermally initiated RAFT emulsion polymerization was compromised due to the hydrolysis and polycondensation of MPS occurring under the reaction conditions employed. A more successful approach to block copolymer self‐assembly was achieved via polymerization in a good solvent for both blocks (1,4‐dioxane) followed by the slow addition of water, yielding spherical nanoparticles that increased in size as the length of the solvophobic block was increased. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 420–429     

DNA‐Assisted Self‐Assembly of Pyrene Foldamers

Folding in the tides : Upon hybridization, pyrene molecules assemble through interstrand stacking interactions to form double‐stranded, helical structures. Structural organization of the pyrene molecules is an intrinsic property of the oligoaryl part and takes place independently of the sequence of the attached DNA. Pyrene helicity is most pronounced in a bi‐segmental chimera, in which a DNA stem is present only at one end of the pyrene section.

     

Carbohydrates as Additives for the Formation of Isoporous PS‐b‐P4VP Diblock Copolymer Membranes

Highly porous polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) diblock copolymer membranes are prepared using carbohydrates as additives. Therefore α‐cyclodextrine, α‐(D )‐glucose, and saccharose (cane sugar) are tested for the membrane formation of three different PS‐b‐P4VP polymers. The addition of the carbohydrates leads to an increasing viscosity of the membrane solutions due to hydrogen bonding between hydroxyl groups of the carbohydrates and pyridine units of the block copolymer. In all cases, the membranes made from solution with carbohydrates have higher porosity, an improved narrow pore distribution on the surface and a higher water flux as membranes made without carbohydrates with the same polymer, solvent ratio, and polymer concentration.     

Self‐Assembled Asymmetric Block Copolymer Membranes: Bridging the Gap from Ultra‐ to Nanofiltration

The self‐assembly of block copolymers is an emerging strategy to produce isoporous ultrafiltration membranes. However, thus far, it has not been possible to bridge the gap from ultra‐ to nanofiltration and decrease the pore size of self‐assembled block copolymer membranes to below 5 nm without post‐treatment. It is now reported that the self‐assembly of blends of two chemically interacting copolymers can lead to highly porous membranes with pore diameters as small as 1.5 nm. The membrane containing an ultraporous, 60 nm thin separation layer can fully reject solutes with molecular weights of 600 g mol^?1 in aqueous solutions with a water flux that is more than one order of magnitude higher than the permeance of commercial nanofiltration membranes. Simulations of the membrane formation process by dissipative particle dynamics (DPD) were used to explain the dramatic observed pore size reduction combined with an increase in water flux.     

Cooperative Self‐Assembly‐Assisted Formation of Monodisperse Optically Active Spherical and Anisotropic Nanoparticles

We report a new method in which spontaneous self‐assembly is employed to synthesize monodisperse polymer nanoparticles with controlled size (<50 nm), shape, tunable functionality, and enhanced solvent and thermal stability. Cooperative noncovalent interactions, such as hydrogen bonding and aromatic π–π stacking, assist self‐assembly of amphiphilic macromolecules (polystyrene‐block‐polyvinylpyridine, PS? PVP) and structure directing agents (SDAs) to form both spherical and anisotropic solid polymer nanoparticles with SDAs residing in the particle core surrounded by the polymers. Through detailed investigations by scanning electron microscopy and transmission electron microscopy (TEM), we have rationalized nanoparticle morphology evolution and dependence on factors such as SDA concentration and PVP size. By keeping the PS chain size constant, the particle morphology progresses from continuous films to spherical particles, and on to cylindrical nanowires or rods with increasing the PVP chain size. The final nanoparticles are very stable and can be redispersed in common solvents to form homogenous solutions and thin films of ordered nanoparticle arrays through solvent evaporation processes. These nanoparticles exhibit tunable fluorescent colors (or emissions) depending on the choices of the central SDAs. Our method is simple and general without requiring complicated synthetic chemistry, stabilizing surfactants, or annealing procedures (e.g., temperature or solvent annealing), making scalable synthesis feasible.     

Polymer/clay nanocomposites through multiple hydrogen‐bonding interactions

An 2‐ureido‐4[1H]pyrimidinone (UPy) motif with self‐association capability (through quadruple hydrogen bonds) was successfully anchored onto montmorillonite clay layers. Polymer/clay nanocomposites were prepared by specific hydrogen bonding interactions between surface functionalized silica nanoclays and UPy‐bonded supramolecular poly(ethylene glycol) or poly(?‐caprolactone). The mixed morphologies including intercalated layers with a non‐uniform separation and exfoliated single layers isolated from any stack were determined by combined X‐ray diffraction and transmission electron microscopic measurements. Thermal analyses showed that all nanocomposites had higher decomposition temperatures and thermal stabilities compared with neat polymer. The differential scanning calorimetric data implied that the crystallinity of polymers did not show essential changes upon introduction of organomodified UPy clays. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 650–658     

Supramolecular Chemistry in the Formation of Self‐Assembled Nanostructures from a High‐Molecular‐Weight Rod–Coil Block Copolymer

The self‐assembled nanostructures of a high‐molecular‐weight rod–coil block copolymer, poly(styrene‐block‐(2,5‐bis[4‐methoxyphenyl]oxycarbonyl)styrene) (PS‐b‐PMPCS), in p‐xylene are studied. The cylindrical micelles, long segmental cylindrical micelle associates, spherical micelles, and spherical micelle associates are observed with increased copolymer concentration. The high molecular weight of PS leads to the entanglement between PS chains from different micelles, which is the force for supramolecular interactions. Short cylindrical micelles are connected end‐to‐end via this supramolecular chemistry to form long segmental cylindrical micelle associates, analogue to the condensation polymerization process, with direction and saturation. On the other hand, spherical micelles assemble via supramolecular chemistry to form spherical micelle associates, yet without any direction due to their isotropic properties.

     

Self‐assembly of well‐defined amphiphilic polymeric miktoarm stars,dendrons, and dendrimers in water: The effect of architecture

Five polymeric architectures with a systematic increase in architectural complexity were synthesized by “click” reactions from a toolbox of functional linear polymers and small molecule linkers. The amphiphilic architectures ranged from a simple 3‐miktoarm star block copolymer to the more complex third generation dendrimer‐like block copolymer, consisting of polystyrene (PSTY) and polyacrylic acid (PAA). Micellization of these architectures in water at a pH of 7 under identical ionic strength gave spherical micelles ranging in size from 9 to 30 nm. Subsequent calculations of the PSTY core density, average surface area per PAA arm on the corona‐core interface, and the relative stretching of the PAA arms provided insights into the effect of architecture on the self‐assembly processes. A particular trend was observed that with increased architectural complexity the hydrodynamic diameter, radius of the core in the dry state and the aggregation number also increased with the exception of the third generation dendrimer. On the basis of these observations, we postulate that thermodynamic factors controlling self‐assembly were the entropic penalty of forming PSTY loops in the core counterbalanced by the reduction in repulsive forces through chain stretching. This results in a greater number of aggregating unimers and consequently larger micelle sizes. The junction points within the architecture also play an important role in controlling the self‐assembly process. The G3 dendrimer showed results contradictory to the aforementioned trend. We believe that the self‐assembly process of this architecture was dominated by the increased attractive forces due to stretching of the PSTY core chains to form a more compact core. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6292–6303, 2009