Curing Behavior and Final Properties of Nanostructured Thermosetting Systems Modified with Epoxidized Styrene‐Butadiene Linear Diblock Copolymers

Nanostructured thermosetting materials based on thermosetting matrices were prepared by modification of an epoxy system with linear PS‐block‐PB copolymers. The nanostructured thermosets were obtained through PS block segregation. Depending on the block‐copolymer content in the thermosets and its epoxidation degree, the PS domains can display micellar, worm‐like or hexagonally‐packed cylinder structures, retaining the stiffness of the epoxy matrix, where the hexagonally cylindrical morphology lead to a significant increase in fracture toughness. The rheokinetics of microphase separation during network formation was investigated. Nanostructures are judged to be formed by polymerization‐induced microphase separation, in marked contrast to equilibrium self‐organized structures that are preformed, with the microphases fixed via a curing reaction.

     

Synthesis and Self‐Assembly of Functionalized Cyclooctene Block Copolymers via ROMP

A novel block copolymer consisted of MACIT and HCO segments was synthesized via ROMP in the ionic liquid [bmim][PF₆] with good control over the polymerization process. The molecular weight of the block copolymer was estimated by ¹H NMR, and the molar composition ratio of repeating units in the MACIT block to those in the HCO block was 100:120 (120:120 in feed). The micellar characterization was carried out by DLS, AFM, and TEM. The hydrodynamic diameter of the micelles, measured by DLS, was 129 ± 0.09 nm with a narrow distribution (PDI = 0.034). The TEM image showed spherical micelles.

     

Self‐Assembly of Globular‐Protein‐Containing Block Copolymers

Self‐assembly has emerged as a powerful approach to control nanostructure in materials containing globular proteins, both through templated self‐assembly and direct self‐assembly of globular protein‐polymer conjugates or fusion proteins. The folded structures of globular proteins that are critical to their function introduce complex shapes and interactions into block copolymers that significantly alter the physics of self‐assembly. This article discusses the different methods for controlling the nanostructure of globular proteins using block copolymers, highlighting efforts at understanding the physics of self‐assembly in concentrated solution and solid‐state bioconjugate copolymers.

     

Role of High‐Molecular‐Weight Homopolymers on Block Copolymer Self‐Assembly: From Morphology Modifier to Template

For block copolymer (BCP)/homopolymer self‐assembly systems, the molecular weight of homopolymers is usually lower than that of BCPs. Herein, the cooperative self‐assembly of polystyrene‐b‐poly(ethylene glycol) (PS‐b‐PEG) BCPs with high‐molecular‐weight polystyrene (PS) homopolymers is reported. The molecular weight of PS homopolymers is 3–63 times that of the PS blocks. Typically, a spherical micelle–vesicle–large sphere morphology transition is observed by increasing the weight fraction of PS homopolymers in the polymer mixtures (f _HP). Dynamic process studies reveal that with adding water to the solution of polymer mixtures in organic solvent, the homopolymers first collapse into globules, and their size increases with f _HP and the molecular weight. Then these PS globules cooperatively self‐assemble with the PS‐b‐PEG BCPs. Depending on their size, these PS globules play different roles in the self‐assembly process. Small PS globules act as morphology modifiers inducing the micelle–vesicle transition, while large PS globules serve as self‐assembly templates for PS‐b‐PEG resulting in large spheres.     

Phase Behavior of Vesicle‐Forming Block Copolymers in Aqueous Solutions

The binary phase diagram of amphiphilic poly(ethylene oxide)‐block‐poly(γ‐methyl‐ε‐caprolactone) block copolymers in water is examined for four polymers having the same hydrophilic block length but different hydrophobic block lengths across the whole concentration range. The bulk polymers show no ordered morphology. With increasing water concentration the polymers undergo transitions from lamellar phases to packed vesicles and subsequently all polymers self‐assemble into vesicles in dilute aqueous solutions. Additionally, the largest polymer forms an inverse hexagonal phase, and the smallest polymer self‐aggregates into rod‐like micelles and showed a hexagonal phase.

     

Solution Self‐Assembly of Core‐Labeled Block Random‐Copolymers Prepared by Ring Opening Metathesis Polymerization

Herein, the synthesis of block random‐copolymers via ring opening metathesis polymerization (ROMP) is presented. A random‐copolymer of norbornene dimethyl ester with different xanthen‐functionalized norbornene derivatives was used as a hydrophobic block while, the hydrophilic part was built from an ethylene glycol‐substituted monomer. The self‐association of these block random‐copolymers in MeOH was strongly influenced by the ionization state of the dye molecules, as shown by a combination of UV–Vis absorption and dynamic light scattering measurements. Aggregate sizes were significantly smaller for samples with charged dye molecules in the core of the aggregate. These findings were attributed to ion pair formation of the charged dye molecules and the according counter ions, thus, inducing strongly attractive dipole–dipole interactions. The optical properties of the dyes under investigation, however, were preserved within the polymer aggregates.

     

Novel Amphiphilic Styrene‐Based Block Copolymers for Induced Surface Reconstruction

This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene‐like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl‐ or amino‐groups after deprotection) were polymerized in a “protected form” to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between ?2 °C to 140 °C for the hydrophilic blocks and ?30 °C to 100 °C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break‐up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water.

     

Two Non‐covalent Methods to Decorate Nanoparticles with Block Copolymers

The physical adsorption of block copolymers is a simple and reliable approach to functionalize the surface of organic or inorganic nanoparticles. This article presents two novel methods of particle coating with block copolymers that may apply to various aqueous colloidal dispersions. The first method relies on the use of charged block copolymers having two adsorbing blocks, which can adopt a typical anchor‐buoy conformation at the particle surface when proper conditions are used. The second approach consists of self‐assembling a bilayer of amphiphilic block copolymers around charged nanoparticles. In both cases, a special emphasis is placed on the process used to control and orient the molecular interactions between the copolymer and the particles.

     

Self‐Assembling of Block Copolymers with Alternative Solvents

Block copolymer (BCP) lithography is one of the most technologically intriguing and scientifically interesting strategies for achieving nanometer‐sized features. This method usually exploits toluene as solvent for the deposition of BCPs in all the processing steps. However, this chemical has some technical disadvantages, such as high toxicity and hygroscopicity. The first aspect can limit its use on the industrial scale because of the protocols on the environmental and operator risks, while the second causes aging effects that can alter the results. In order to overcome these intrinsic limitations, a BCP self‐assembly (BCP‐SA) strategy is presented by using alternative deposition solvents in place of toluene. A preliminary study, based on the physical characteristics, such as volatility, polarity, and hygroscopicity, is carried out to explore two new alternative solvents, ethyl acetate and tetrahydrofuran. The effects on the BCP‐SA due to the new solvents are studied by SEM analysis supported by suitable software for the images elaboration. The results achieved show very promising outcomes for the polymer solutions obtained with ethyl acetate, in terms of uniformity of geometrical features, ordered areas extension, and homogeneity of the pattern obtained, making this chemical a good alternative to toluene.     

Synthesis and Association Behaviour of Linear Block Copolymers with Different Microstructures but the Same Composition

The di‐ and triblock copolymers, P(MAA)‐b‐P(MMA), P(MAA)‐b‐P(BMA), P(MAA)‐b‐P(MAA‐co‐MMA)‐b‐P(MMA) and P(MAA)‐b‐P(MAA‐co‐BMA)‐b‐P(BMA), were synthesised via ATRP in order to study the association behaviour in water via polyelectrolyte titration, fluorescence spectroscopy, dynamic light scattering and scanning force microscopy. P(BMA) block copolymers spontaneously self‐associate into micelles whereas for P(MMA) block copolymers addition of salt is necessary to induce aggregation. Principally, the hydrodynamic radius of the micelles decreases from di‐ to triblock copolymer which was attributed to a different conformation of the random middle block at the core/corona interface.

     

SET‐LRP Synthesis of Well‐Defined Light‐Responsible Block Copolymer Micelles

Herein, the synthesis of well‐defined light‐sensitive amphiphilic diblock copolymers consisting of UV‐responsive poly(2‐nitrobenzyl acrylate) (PNBA) and hydrophilic poly(ethylene oxide) (PEO) blocks is reported. This is achieved by a single electron transfer living radical polymerization (SET‐LRP) of 2‐nitrobenzyl acrylate monomer initiated by PEO‐containing macroinitiator. Despite several reports on PEO‐b‐PNBA copolymers, this is the first time the PNBA block is synthesized by a controlled radical polymerization leading to the copolymers with low dispersity (Ð = 1.10). In water, the copolymers self‐assemble into well‐defined micelles with a hydrodynamic diameter of 25 nm. Upon irradiation with UV‐light, the PNBA units degrade to hydrophilic poly(acrylate) resulting in disassembly of the micelles. Considering the robustness of the reported synthetic protocol, the prepared polymers represent an interesting platform for the construction of new stimuli‐responsive drug delivery systems.     

Synthesis of Photocleavable Amphiphilic Block Copolymers: Toward the Design of Photosensitive Nanocarriers

The synthesis of a novel amphiphilic block copolymer containing a photodegradable linker as a junction point between hydrophilic and hydrophobic chains is presented. PmCL–ONB–PAA block copolymers were synthesized via a combination of ROP and ATRP from a difunctional photoresponsive initiator (ONB). The copolymers are biodegradable and biocompatible, they can self‐assemble into different structures, including micelles and vesicles which are photoresponsive. When polymer solutions were exposed to UV we observed significant changes in size and number of particles. We are currently investigating the promising potential of this system as photosensitive nanocarrier.

     

Poly(hydroxyl propyl methacrylate)‐b‐Poly(oligo ethylene glycol methacrylate) Thermoresponsive Block Copolymers by RAFT Polymerization

Thermoresponsive amphiphilic poly(hydroxyl propyl methacrylate)‐b‐poly(oligo ethylene glycol methacrylate) block copolymers (PHPMA‐b‐POEGMA) are synthesized by RAFT polymerization, with different compositions and molecular weights. The copolymers are molecularly characterized by size‐exclusion chromophotography, and ¹H NMR spectroscopy. Dynamic light scattering (DLS) and static light scattering (SLS) experiments in aqueous solutions show that the copolymers respond to temperature variations via formation of self‐organized nanoscale aggregates. Aggregate structural characteristics depend on copolymer composition, molecular weight, and ionic strength of the solution. Fluorescence spectroscopy experiments confirm the presence of less hydrophilic domains within the aggregates at higher temperatures. The thermoresponsive behavior of the PHPMA‐b‐POEGMA block copolymers is attributed to the particular solubility characteristics of the hydrophilic, water insoluble PHPMA block that are modulated by the presence of the water soluble POEGMA block.     

Polylactide/Perfluoropolyether Block Copolymers: Potential Candidates for Protective and Surface Modifiers

Perfluoropolyethers are a well known and widely used family of polymers, suitable as protectives. Their main drawback is the lack of solubility, which is complete only in chlorofluorocarbons. In this work a series of A‐B‐A block copolymers (FluoPLA), with a relative low molecular weight, were prepared by ROP of L ‐ and D ,L ‐lactide (PLA) in the presence of a hydroxy‐terminated perfluoropolyether as macroinitiator. In fact the use of block copolymers leads to different advantages, i.e. a limited segregation phenomena and higher polymer solubility. The resulting polymers were characterized (by NMR, IR, HPLC‐SEC, DSC, LS) and tested as potential protective and surface modifiers for cultural heritage (ESEM‐EDS, solar‐box technique, colorimeter analysis).

     

Star Block Copolymers Through Nitroxide‐Mediated Radical Polymerization From Polyhedral Oligomeric Silsesquioxane (POSS) Core

A series of star block copolymers were prepared through nitroxide‐mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core‐first polymerization. Eight N‐alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q₈M POSS) with 1‐(2‐(allyloxy)‐1‐phenylethoxy)‐2,2,6,6‐tetramethylpiperidine (allyl‐TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa‐N‐alkoxyamines POSS (OT‐POSS) were used as platform to synthesize star polystyrene‐POSS ((PS)₈‐POSS) homopolymer and diblock copolymers of poly(styrene‐block‐4‐vinylpyridine)‐POSS ((PS‐b‐P4VP)₈‐POSS) and poly(styrene‐block‐acetoxystyrene) ((PS‐b‐PAS)₈‐POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS‐b‐PAS)₈‐POSS, the poly(styrene‐block‐vinyl phenol) ((PS‐b‐PVPh)₈‐POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self‐assembled structures of these star block copolymers based on POSS were characterized by ¹H NMR, FTIR, SEC, TEM, and SAXS analyses.

     

Synthesis and Self‐Assembly of Novel Amphiphilic Six‐Armed Star Copolymers TP[PDMAEMA‐b‐PSt]6

A triphenylene (TP)‐based hexafunctional initiator was prepared and used in successive ATRP of DMAEMA and St. Well‐defined six‐armed star block copolymers TP[PDMAEMA‐b‐PSt]₆ bearing hydrophilic backbones inside and hydrophobic blocks outside were successfully synthesized. The self‐assembly behaviors of the novel amphiphilic copolymer were further investigated. Co‐existing spherical and bowl‐shaped aggregates were observed from their neutral aqueous solution, while large spherical structures with different dimensions were obtained from their diluted HCl and CF₃COOH aqueous solution, respectively. Dynamic light scattering in different aqueous solutions were conducted to give further confirmation. The possible mechanism of the morphology formation was proposed.

     

Design and Fabrication of Janus Nanoparticles for Interfacial Distribution in Block Copolymers

Hybrid composites with highly ordered structures show promise for applications in various fields and thus there is great interest in their fabrication. In this context, Janus nanoparticles (JNPs) are synthesized with the aim of further incorporating them into polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) block copolymers to fabricate hybrid composites. It is observed that the dispersed JNPs are located at the boundary of the two morphological phases in PS‐b‐P2VP. The orientation of the lamellar structure in the bottom and free surface region of the block copolymer (BCP) composites shows a distinct difference as the composition of the JNPs is adjusted. The processing conditions of the nanoparticle/BCP composites are found to play an important role in achieving the desired structures.

     

Aggregation and Crosslinking of Poly(N,N‐dimethylacrylamide)‐b‐pullulan Double Hydrophilic Block Copolymers

The self‐assembly of polymers is a major topic in current polymer chemistry. In here, the self‐assembly of a pullulan based double hydrophilic block copolymer, namely pullulan‐b‐poly(N,N‐dimethylacrylamide)‐co‐poly(diacetone acrylamide) (Pull‐b‐(PDMA‐co‐PDAAM)) is described. The hydrophilic block copolymer induces phase separation at high concentration in aqueous solution. Additionally, the block copolymer displays aggregates at lower concentration, which show a size dependence on concentration. In order to stabilize the aggregates, crosslinking via oxime formation is described, which enables preservation of aggregates at high dilution, in dialysis and in organic solvents. With adequate stability by crosslinking, double hydrophilic block copolymer (DHBC) aggregates open pathways for potential biomedical applications in the future.     

Tetraphenylsilane‐Cored Star‐Shaped Amphiphilic Block Copolymers for pH‐Responsive Anticancer Drug Delivery

Four‐arm star‐shaped poly[2‐(diethylamino)ethyl methacrylate]‐b‐poly[2‐hydroxyethyl methacrylate]s block copolymers using tetraphenylsilane (TPS) as a core with adjustable arm lengths are synthesized through two‐step atom transfer radical polymerizations. For comparison, a linear block copolymer with similar molecular weight is also prepared. The assembled star‐shaped copolymer micelles exhibit sizes of 102–139 nm and critical micelle concentrations of 1.49–3.93 mg L^?1. Moreover, the bulky and rigid TPS core is advantageous for propping up the four star‐shaped arms to generate large intersegmental space. As a result, the drug‐loading capacity in the micelles is up to 33.97 wt%, much surpassing the linear counterpart (8.92 wt%) and the previously reported star‐shaped copolymers prepared using pentaerythritol as the core. Furthermore, the micelles show sensitive pH‐responsive drug release when the pH changes from 7.4 to 5.0. The in vitro cytotoxicity to Hela cells indicates that the doxorubicin (DOX)‐loaded micelles have similar anticancer activity to the pristine DOX. The combination of excellent micelle stability, high drug‐loading, sensitive pH response, and good anticancer activity endows the copolymers with promising application in drug control delivery for anticancer therapy.     

Anionic Grafting to Strategies for Functional Polymethacrylates: Convenient Preparation of Stimuli‐Responsive Block Copolymer Architectures

Functional block copolymers (BCP) are promising candidates for many important applications in fields of separations technologies, drug delivery, or (nano)lithography. Here, a universal strategy is described for the preparation of functional poly(methacrylate)s grafted (PMA) to polystyrene‐block‐polyisoprene (PS‐b‐PI) BCPs via a convenient postmodification strategy. PS‐b‐PIs are functionalized by means of hydrosilylation protocols for the introduction of chlorosilane moieties. Subsequent anionic grafting‐to polymerization of different functional PMA macro anions leads to grafted BCP. Various functional and non‐functional homopolymers, that is, poly(di(ethylene glycol) methyl ether methacrylate), poly(methacrylic acid), and poly(3‐methacryloxypropyl)heptaisobutyl‐T8‐silsesquioxane as well as poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(iso‐propyl methacrylate), poly(tert‐butyl methacrylate), and poly(2‐hydroxy ethyl methacrylate) are block‐selectively incorporated into the PI segment. Applied grafting strategies for the non‐functional PMA derivatives, which feature different sizes of the alkyl substituent, reveal a strong influence on the grafting‐to efficiency. The grafted BCP architectures are capable of undergoing microphase separation in the bulk state, while the resulting morphology is significantly influenced by the introduction of PMA segments as shown by transmission electron microscopy measurements. Additionally, the structure formation and pH‐switching capability of the poly(methacrylic acid)‐grafted BCP is studied by dynamic light scattering, proving the feasibility for the herein investigated synthesis strategy.