Nanoparticles block copolymers

Self-Assembly of Nanoparticle/Block Copolymer Mixtures. 50... 

Cao, D. and Wu, J. (2007) Density functional theory for a primitive model of nanoparticle-block copolymer mixtures. Journal of Chemical Physics, 126,144912. 

Figure 7.12 Theoretical phase diagram of hybrid nanoparticle/block copolymer surfactant micelles in solution. Here, Cp is the particle volume fraction (volume fraction of the surfactant is fixed at 5%), D stands for...

Figure 6 Bright-field TEM images of nanostructured Pt metal/ PI-/>-PDMAEMA block copolymer composites (a) spherical micellar morphology (b) wormlike cylinders morphology (c) lamellar morphology and (d) inverse hexagonal morphology. From Z. Li, H. Sai, S. C. Warren, M. Kamperman, H. Arora, S. M. Gruner, U. Wiesner, Metal Nanoparticle/Block Copolymer Composite Assembly and Disassembly, Chem. Mater. 21 (2009), 5578-5584, Figure 3.

Qi, L. Colfen, H. and Antonietti, M. (2001). Synthesis and Characterization of CdS Nanoparticles Stabilised by Double Hydrophilic Block Copolymers. Nano Lett, 1, 61-65. 

Youk J.H., Park M.K., Locklin J., Advincula R., Yang J., and Mays J. Preparation of aggregation stable gold nanoparticles using star-block copolymers, Langmuir, 18, 2455, 2002. 

Tian, L. and Hammond, P.T. Comb-dendritic block copolymers as tree-shaped macromolecular amphi-philes for nanoparticle self-assembly, Chem. Mater., 18, 3976, 2006. 

In 2000, the first example of ELP diblock copolymers for reversible stimulus-responsive self-assembly of nanoparticles was reported and their potential use in controlled delivery and release was suggested [87]. Later, these type of diblock copolypeptides were also covalently crossUnked through disulfide bond formation after self-assembly into micellar nanoparticles. In addition, the encapsulation of l-anilinonaphthalene-8-sulfonic acid, a hydrophobic fluorescent dye that fluoresces in hydrophobic enviromnent, was used to investigate the capacity of the micelle for hydrophobic drugs [88]. Fujita et al. replaced the hydrophilic ELP block by a polyaspartic acid chain (D ). They created a set of block copolymers with varying... 

Scheme 2. Encapsulation of size- and shape-controlled Pt nanoparticles under neutral hydrothermal synthesis conditions of SBA-15. Silica templating block copolymers and silica precursors were added to PVP-protected Pt nanoparticle solutions and subjected to the standard SBA-15 silica synthesis conditions. Neutral, rather than acidic pH conditions were employed to prevent particle aggregation and amorphous silica formation [16j. (Reprinted from Ref. [16], 2006, with permission from American Chemical Society.)...

A. Haryono and W. H. Binder, Controlled arrangement of nanoparticle arrays in block-copolymer domains, Small, 2006, 2, 600. 

Abstract This chapter gives an overview of the research on the self-assembly of amorphous block copolymers at different levels of hierarchy. Besides the influence of composition and topology on the morphologies of block copolymers with linear, cyclic and branched topologies blends of block copolymers with low molecular weight components, other polymers or block copolymers and nanoparticles will also be presented. 

Influence on the phase behaviour is observed if even small amounts (0.5 wt %) of hairy silica-like nanoparticles obtained by block-copolymer-directed sol-gel synthesis are added to a block copolymer [53,214]. On the example of a PS-fo-PI diblock copolymer a depression of the ODT of approx. 20 K was observed (Fig. 68), accompanied by a broadening of the transition. The largest depression was observed for rod-like nanoparticles, which is explained by the energy introduced by the defects [215]. 

Recently, many studies have focused on self-assembled biodegradable nanoparticles for biomedical and pharmaceutical applications. Nanoparticles fabricated by the self-assembly of amphiphilic block copolymers or hydrophobically modified polymers have been explored as drug carrier systems. In general, these amphiphilic copolymers consisting of hydrophilic and hydrophobic segments are capable of forming polymeric structures in aqueous solutions via hydrophobic interactions. These self-assembled nanoparticles are composed of an inner core of hydrophobic moieties and an outer shell of hydrophilic groups [35, 36]. 

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

The formation of stable nanoparticles has been studied using various derivatives of thermosensitive PNIPAM, including diblock and graft copolymers, PNIPAM-b-PEO and PNIPAM-g-PEO [165-172], In these copolymers, the role of the PEO chains is to solubilise/stabilise collapsed PNIPAM at temperatures above its cloud point. Both the graft and the block copolymers, PNIPAM-g-PEO and PNIPAM-fr-PEO, form spherical core-shell structures in... 

Partial hydrogenation of acetylenic compounds bearing a functional group such as a double bond has also been studied in relation to the preparation of important vitamins and fragrances. For example, selective hydrogenation of the triple bond of acetylenic alcohols and the double bond of olefin alcohols (linalol, isophytol) was performed with Pd colloids, as well as with bimetallic nanoparticles Pd/Au, Pd/Pt or Pd/Zn stabilized by a block copolymer (polystyrene-poly-4-vinylpyridine) (Scheme 9.8). The best activity (TOF 49.2 s 1) and selectivity (>99.5%) were obtained in toluene with Pd/Pt bimetallic catalyst due to the influence of the modifying metal [87, 88]. 

Colloidal catalysts in alkyne hydrogenation are widely used in conventional solvents, but their reactivity and high efficiency were very attractive for application in scC02. This method, which is based on colloidal catalyst dispersed in scC02, yields products of high purity at very high reactions rates. Bimetallic Pd/Au nanoparticles (Pd exclusively at the surface, while Au forms the cores) embedded in block copolymer micelles of polystyrene-block-poly-4-vinylpyridine... 

In a more general way, the loading of metal salts into preformed block copolymer micelles has become the most used route for the incorporation of precursors into block copolymer nanostructures because it allows precursor loading with tolerable loading times, it is quite versatile, and it is applicable to a wide variety of precursor/block copolymer/solvent systems. The accordingly synthesized polymer-coated metallic or semiconducting nanoparticles exhibit increased stability, which results in, e.g., protection against oxidation as illustrated by Antonietti et al. [108]. 

Fig. 9 Gold nanoparticles (left hand side of the image) prepared by deposition onto a nanoporous PS mask derived form a PS-PMMA block copolymer. Reproduced from refernence [33]... 

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