Class Of Block Copolymers Research Articles

Unraveling the Photoluminescence Properties of a Boron Nitride Nanosheet Dispersed in Different Solvents and Its Application to Generate White Light.

Hexagonal boron nitride (h-BN) is an influential 2D nanomaterial; however, its practical optoelectronic applications rely primarily on controlling the structural defects. The photoluminescence depends explicitly on the developed vacancies and substitutional defects. The present work utilizes the concept of facile liquid-phase exfoliation of hexagonal (h) boron nitride (BN) powder in common organic solvents and cosolvent mixtures to obtain a layered boron nitride nanosheet (BNNS). Although the literature concerning the layered structure of BNNS obtained by different methods is substantial, what is lacking is a detailed photoluminescence study of the layered structure obtained by changing the solvent and cosolvent mixtures, and here lies the novelty of our work. The obtained layered structure was subjected to a detailed photoluminescence study by varying the temperature. We tried to correlate how the defects originating upon changing the solvent and cosolvent affected the photoluminescence of the layered BNNS. The obtained layered structure is suitably supported by optical and electron microscopy images. High-resolution transmission electron microscopy confirm the presence of a few layers, and X-ray photoelectron spectroscopy studies give an idea of the atomic composition of the obtained BNNS. The photoluminescence properties of the obtained BNNS in water were modulated by the addition of two different classes of block copolymers, e.g., Pluronic (F-68, P-407, and P-123) and Tetronic (T-904, T-908, and T-90R4) copolymers. As an application, we were successful in constructing a nanocomposite material made up of a BNNS-copolymer-organic fluorophore to check the possibilities of generating white light.

Volume fraction and width of ribbon-like crystallites control the rubbery modulus of segmented block copolymers

Abstract We discuss the origin of the plateau modulus enhancement (χ) in semi-crystalline segmented block copolymers by increasing the concentration in hard segments within the chains (X HS). The message we deliver is that the plateau modulus of these thermoplastic elastomers is greatly dominated by the volume fraction (Φ) and the width (W) of crystallites according to χ–1 ~ ΦW in agreement with a recent topological model we have developed. We start by a quick review of literature with the aim to extract χ(Φ) for different chemical structures. As we suspected, we find that most of the data falls onto a mastercurve, in line with our predictions, confirming that the reinforcement in such materials is mainly dominated by the crystallite’s content. This important result is then supported by the investigation of copolymer mixtures in which Φ is fixed, providing a similar reinforcement, while the chains compositions is significantly different. Finally, we show that the reinforcement can be enhanced at constant Φ by increasing W for a given class of block copolymers. This can be done by changing the process route and is again in good agreement with our expectations.

Polypept(o)ides: Hybrid Systems Based on Polypeptides and Polypeptoids

Polypept(o)ides combine the multifunctionality and intrinsic stimuli-responsiveness of synthetic polypeptides with the "stealth"-like properties of the polypeptoid polysarcosine (poly(N-methyl glycine)). This class of block copolymers can be synthesized by sequential ring opening polymerization of α-amino acid N-carboxy-anhydrides (NCAs) and correspondingly of the N-substituted glycine N-carboxyanhydride (NNCA). The resulting block copolymers are characterized by Poisson-like molecular weight distributions, full end group integrity, and dispersities below 1.2. While polysarcosine may be able to tackle the currently arising issues regarding the gold standard PEG, including storage diseases in vivo and immune responses, the polypeptidic block provides the functionalities for a specific task. Additionally, polypeptides are able to form secondary structure motives, e.g., α-helix or β-sheets, which can be used to direct self-assembly in solution. In this feature article, we review the relatively new field of polypept(o)ides with respect to synthesis, characterization, and first data on the application of block copolypept(o)ides in nanomedicine. The summarized data already indicates the great potential of polypept(o)ides.

Fabrication of Bioactive Surfaces by Functionalization of Electroactive and Surface-Active Block Copolymers.

Biofunctional block copolymers are becoming increasingly attractive materials as active components in biosensors and other nanoscale electronic devices. We have described two different classes of block copolymers with biofuctional properties. Biofunctionality for block copolymers is achieved through functionalization with appropriate biospecific ligands. We have synthesized block copolymers of electroactive poly(3-decylthiophene) and 2-hydroxyethyl methacrylate by atom transfer radical polymerization. The block copolymers were functionalized with the dinitrophenyl (DNP) groups, which are capable of binding to Immunoglobulin E (IgE) on cell surfaces. The block copolymers were shown to be redox active. Additionally, the triblock copolymer of α, ω-bi-biotin (poly(ethylene oxide)-b-poly (styrene)-b-poly(ethylene oxide)) was also synthesized to study their capacity to bind fluorescently tagged avidin. The surface-active property of the poly(ethylene oxide) block improved the availability of the biotin functional groups on the polymer surfaces. Fluorescence microscopy observations confirm the specific binding of biotin with avidin.

Ring-Opening Metathesis Polymers for Biodetection and Signal Amplification: Synthesis and Self-Assembly

The ring-opening metathesis polymerization (ROMP) was used to develop a new class of block copolymers toward biological detection with signal amplification. For this, three classes of ROMP monomers were synthesized: (i) luminescent and electrochemiluminescent transition-metal-containing monomers, with ruthenium, osmium, and iridium bipyridine units, (ii) biologically compatible monomers and macromonomers containing oligothylene glycol units, and (iii) bioconjugatable monomers as well as monomers containing the biorecognition unit biotin. ROMP was used to efficiently combine these monomers into amphiphilic di- and triblock copolymers. Self-assembly of these block copolymers in aqueous media generates micellar spherical assemblies, which contain a large number of luminescent transition-metal centers in their core, a biocompatible and biologically inert protecting shell, and biological recognition units or bioconjugatable groups on their periphery. These micelles can act as luminescent markers for biological molecules with potential for signal amplification. In addition, the monomers and polymers reported here can serve as useful biologically enabled building blocks for a number of applications, including drug delivery and tissue engineering.

A Facile Preparative Method for Aggregation‐Free Gold Nanoparticles Using Poly(styrene‐block‐cysteine)

In a stable condition: The self-assembly and induced assembly of a new class of block copolymers containing polystyrene (PS) and polycysteine (PCys) is investigated (see picture). The efficiency of these “molecular chimeras” to encapsulate gold nanoparticles (AuNPs), and thereby enhance their stability against aggregation, is also demonstrated.

Solid‐State Structure, Organization and Properties of Peptide‐Synthetic Hybrid Block Copolymers

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Polymeric Micelles for Drug Delivery

Polymeric micelles are nanoscopic core/shell structures formed by amphiphilic block copolymers. Both the inherent and modifiable properties of polymeric micelles make them particularly well suited for drug delivery purposes. An emphasis of this review has been placed on both the description and characterization techniques of the physical properties of polymeric micelles. Relevant properties discussed include micellar association, morphology, size and stability. These properties and characterization techniques are included to provide context for the known advantages and applications of polymeric micelles for drug delivery. The advantages and applications discussed include solubilization of poorly soluble molecules, sustained release and size advantages, and protection of encapsulated substances from degradation and metabolism. The three most widely studied block copolymer classes are characterized by their hydrophobic blocks, and are poly(propylene oxide), poly(L-amino acid)s and poly(ester)s. These three classes of block copolymers are reviewed with multiple examples of current research in which formulation techniques with polymeric micelles have been applied to some of the most challenging molecules in the pharmaceutical industry. The polymeric micelles used for drug delivery in these examples have shown the abilities to attenuate toxicities, enhance delivery to desired biological sites and improve the therapeutic efficacy of active pharmaceutical ingredients.

Complex associates of plasmid DNA and a novel class of block copolymers with PEG and cationic segments as new vectors for gene delivery

Cationic block copolymers, consisting of a poly(ethylene glycol) block and a block deriving from the poly(dimethylamino)ethyl methacrylate were prepared via a two-step procedure, based on the use of macroinitiators. By appropriately changing the experimental conditions and reacting the poly(dimethylamino)ethyl methacrylate block with iodo- or bromo-alkyl derivatives, a variety of ionic block copolymers with tuned physicochemical properties were prepared. These block copolymers are able to spontaneously self-assemble with plasmid DNA to produce oriented and shielded vectors, with physicochemical properties appropriate for in vivo applications. In addition, the formation of a complex between the cationic block copolymer and the plasmid DNA results in a nuclease resistance increase due to the stable nature of the complex.

Atomic force microscopy studies of molded thin films of segmented polyamides

Block copolymers comprise two or more blocks of chemically different monomers. If the blocks are sufficiently large and the interactions between them sufficiently adverse, the blocks will segregate [1, 2]. Since the blocks are inter connected, they can only segregate on a microscopic scale. For example, an AB diblock copolymer with A and B blocks of equal molecular weight will form a mesophase structure of A and B lamellae. The thickness of the lamellae is commensurate with the size of the polymer coil. A particularly interesting type of block copolymer is the ABA triblock copolymer where A constitutes a thermoplastic material (e.g., polystyrene) and B an elastomer (e.g., polybutadiene). Another interesting class of block copolymers is the (AB)n type of copolymers where “A” represents the soft segment and “B” corresponds to the hard block. Segmented polyamides composed of polyether and polyamide structural units is a typical example of (AB)n type block copolymers. Since the structural units are linked via an ester group, such systems are also referred to as polyether – ester – amides [3, 4] having the chain structure as shown below.

Hybrid thermotropic liquid‐crystalline block copolymers

AbstractA new approach to the preparation of two classes of block copolymers containing liquid‐crystalline segments is reported. Copolymers 1 and 2 are constituted by polytetrahydrofuran and side‐chain liquid‐crystalline polymethacrylate blocks, whereas block copolymers 3 consist of polystyrene and main‐chain liquid‐crystalline polyester blocks. The synthetic procedures leading to copolymers 1‐3 are extremely versatile and can be used to prepare a great variety of block copolymer architectures. In both copolymer classes the chemically different blocks are strongly segregated in the solid and melt phases and undergo individual phase transitions. The mesophase transition temperatures of the liquid‐crystalline blocks are very similar to those of the corresponding homopolymers, and their enthalpies are directly proportional to the content of the liquid‐crystalline block.