Diblock Copolymer Nanocomposites and Metal Nanocrystal Hybrid Nanoparticles Incorporating Polyhedral Oligomeric Silsesquioxane Building Blocks

• Main Authors: Lu, Chu-Hua, 呂居樺
• Other Authors: Chang, Feng-Chih
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/58629492868016003534

博士 === 國立交通大學 === 應用化學系所 === 97 === Nanomaterials are defined as materials having at least one dimension ranging in size from 1 to 100 nm. One-dimensional NPs (NPs) have been prepared with many different compositions and functions. In our review of the literature in Chapter 1 of this Thesis, we separate NPs from nanocrystals (NCs) that exhibit ordered packing of their compositional atoms or ions in confined nanodomains. Nanocrystals can be further divided, according to their compositions, into metal NCs and ionic NCs. Similarly, NPs can be further divided into inorganic, organic, and inorganic/organic hybrid NPs. In addition to aggregate or cluster NPs, some well-defined chemical structures can be regarded as molecular NPs. In this thesis, gold and palladium NCs (Au, Pd NCs) are classified as metal NCs and polyhedral oligomeric silsesquioxane (POSS) derivatives are classified as molecular inorganic/organic hybrid NPs; in addition, pure micelles of block copolymers and their metal NC-incorporated congeners are considered to be aggregate organic NPs and aggregate inorganic/organic hybrid NPs, respectively. Chemical and solvothermal reductions are discussed in a reviewing of the methods of preparation of Au, Ag, Pd, and Pt NCs. Amphiphilic block copolymers are the focus of a great deal of research because of their ability to self-assemble into well-defined nanostructures that have the potential to function as nanosized reactors or storage vessels. The two immiscible high-molecular-mass blocks of poly(ε-caprolactone)-block-poly(4-vinylpyridine) (PCL-b-P4VP) have a positive mixing enthalpy (ΔH) and nearly-zero mixing entropy (ΔS); as a result, PCL-b-P4VP can thermodynamically self-assemble into microstructures featuring regions of distinct phase separation [positive mixing free energy (ΔG = ΔH – TΔS)]. The pyridine units of the P4VP block can function as a polymeric metal ligand for the stabilization of metal ions and for the nanoscale storage of metal NPs. Chapter 2 describes the development of a simple difunctional initiator containing hydroxyl and N-alkoxyamine groups for the living ring-opening polymerization of ε-CL and the controllable nitroxide-mediated polymerization of 4-VP. POSS derivatives have a well-defined chemical structure (RSiO1.5)8 of eight alkyl or aryl chains (R) presented at the corners of a cubic siloxane cage (Si8O12). Similar to organic molecules, POSS colloids, with their insoluble siloxane cubes, can crystallize from organic solvents into ordered structures. Unfortunately, Pt(0)-mediated hydrosilylation of octakis-functionalized POSS derivatives yields products possessing both α- and β-isomeric linkages, which suppress the crystallization of POSS colloids, resulting in amorphous liquids and glasses. Nevertheless, such compound feature eight functional groups dispersed in eight directions from the corners of the 1-nm-diameter POSS core, providing POSS-based nanocomposites exhibiting high degree of chemical modification and low steric hindrance. Chapter 3 describes the incorporation of eight N-alkoxyamine groups onto a POSS cage and its use in the preparation of eight-arm star polystyrene [POSS-(PS)8] and star-block polystyrene-block-poly(4-vinylpyridine) [POSS-(PS-b-P4VP)8] and polystyrene-block-poly(4-vinylphenol) [POSS-(PS-b-PVPh)8] derivatives. The kinetics of the polymerization of POSS-(PS)8 were similar to that of linear PS, indicating the ability to form excellent-quality star polymers from this low-steric-hindrance POSS-based multi-initiator. Chapter 2 describes amphiphilic PCL-b-P4VP copolymers that are capable of transferring HAuCl4 from water to dichloromethane in ionic form [NH(AuCl4)]. Subsequent reduction with NaBH4 and micellization with excess toluene (a selective solvent for the P4VP blocks) provided micelle-protected gold NCs (Au NCs) that could be dispersed well in organic solvents. Because the organically encapsulated Au NCs exhibited decreased activity for their surface reactions, we employed bulky protective groups with relatively large interparticlar distances to improve the reactivity of the surface atoms of the NCs. In the reported structures of POSS crystal, the lattice constant a is usually larger than the diameter of the POSS molecule, suggesting that desolvation occurs after packing of the POSS colloids. Chapter 4 describes POSS-Au hybrid NPs prepared from a thiol-monofunctionalized isobutyl-POSS (SH-POSS). As expected, the absorption of 1.3-nm-diameter SH-POSS colloids onto the surface of ca. 2-nm-diameter Au NPs through dynamic Au–S bonds suppressed the crystallization of the SH-POSS colloids, resulting in amorphous POSS-Au hybrid NPs. Excess SH-POSS colloids formed a crystalline POSS template for the surface self-assembly of POSS-Au hybrid NPs, resulting in novel fernlike microstructures. The use of such a POSS derivative as a protective agent provides an excellent dispersion of Au NCs in the condensed phase or in organic solvents. Palladium NCs (Pd NCs) are well-known catalysts for many carbon–carbon bond-forming reactions, including Suzuki and Heck couplings. Thus, POSS-Pd hybrid NPs are expected to be a highly reactive catalysts because of the large interstices between the absorbed SH-POSS colloids on the surfaces of the Pd NCs. Chapter 5 describes a reductant-free method for preparing POSS-Pd hybrid NPs by refluxing a toluene solution containing palladium acetate and thiol compounds, namely SH-POSS and 1-dodecanthiol (SH-C12). The Heck couplings of methyl acrylate with iodobenzene using the POSS-Pd and C12-Pd hybrid NPs as catalysts revealed the better activity of the former hybrid NPs. Chapter 6 presents a summary of the four major accomplishments described in this thesis: (i) the low-temperature preparation of N-alkoxyamine adducts for nitroxide-mediated radical polymerization, (ii) the living polymerization of a well-defined star PS and related star-block copolymers, (iii) a crystalline template of POSS colloids that incorporate POSS-Au hybrid NPs to give novel fernlike microstructures, and (iv) the low-temperature solvothermal reduction of POSS-Pd hybrid NPs that function as excellent catalysts for the Heck coupling of methyl acrylate and iodobenzene.