多面體聚矽氧烷為建構單元的嵌段式共聚物奈米複合材料及金屬晶粒複合奈米粒子

Abstract

奈米材料(nanomaterials)泛指一維空間尺度在1到100奈米的材料，我們可以發現很多的零維奈米粒子(nanoparticles, NPs)可以有很多不同的組成及功能；在第一章檢閱目前的文獻，我們將奈米晶粒(nanocrystals, NCs)從奈米粒子(NPs)分類出來，因為它們的奈米結構是由原子或離子有序堆積組成。奈米晶粒(NCs)根據組成可再細分為金屬奈米晶粒(metal NCs)及離子奈米晶粒(ionic NCs)；同理，其它奈米粒子(NPs)可細分為無機(inorganic NPs)、有機(organic NPs)及無機有機混成(inorganic/organic hybrid NPs)的奈米粒子。有些奈米粒子(NPs)有特定單一的化學結構可在歸類為分子型奈米粒子(molecular NPs)，相較於其它的，凝聚或叢集型奈米粒子(aggregative or cluster NPs)。此研究的無機有機混成的奈米複合粒子(inorganic/organic hybrid NPs)包括：嵌段式共聚物微胞保護的奈米金晶粒(PCL-b-P4VP-protected Au NPs)、嵌段式共聚物接枝的多面體聚矽氧烷[POSS-(PS)8, POSS-(PS-b-P4VP)8, POSS-(PS-b-P4VP)8]、多面體聚矽氧烷(POSS)保護奈米金晶粒(POSS-Au hybrid NPs)及鈀晶粒(POSS-Pd hybrid NPs)。 有很多有趣的研究討論雙親性嵌段式共聚物可自組裝成很多有序奈米結構做為奈米反應器或儲存器，對聚七環ε-型己內酯及聚對位乙烯吡啶的嵌段式共聚物[poly(ε-caprolactone)-block-poly(4-vinylpyridine)，命名為PCL-b-P4VP]，二個互不相溶的長鏈高分子致使他們的混合焓(ΔH> 0)為正混合熵(ΔS~0)接近零，在熱力學上這兩鏈段會自組裝成明顯相分離的微結構，因為它們的混合自由能為正值[ΔG= ΔH-TΔS)> 0]。聚對位乙烯吡啶的吡啶單元可做為高分子型金屬螯合劑做為奈米儲存器用來穩定金屬離子或金屬奈米粒子，此研究的第二章，我們開發一種較簡易的方法用來製備雙官能基起始劑包含醇基(hydroxyl)及烷氧胺基(N-alkoxyamine)的基團用來活性開環聚合對聚七環ε-型己內酯及可控制氮氧化物為媒介自由基聚合對位乙烯吡啶。 多面體聚矽氧烷(POSS)有特定單一的化學結構(RSiO1.5)8包含八個有機基團(R)共價性鍵結在矽烷氧的笼狀立方體的八個端點(SiO1.5)8，這樣的結構可歸類為分子型無機有機混成奈米粒子(molecular inorganic and organic hybrid NPs)；與小分子相似，POSS的膠體(溶劑溶解的有機殼層包覆不可溶的無機核心)也能有序堆積成固態膠體結晶。可惜的是，用零價鈀催化的矽氫加成修飾的八官能基有不同構型的異構物分別為分枝的α型(-Si-CH(CH3)-R)和線狀的β型(-Si-CH2CH2-R)，這樣的異構物會抑制POSS的有序堆積(膠體結晶)，讓八官能基的POSS產物呈現非晶型的液體或玻璃狀的固體。然而，含八個有機基團在1奈米大小的POSS膠體的八個方位，這樣的化合物可預期良好的反應特性(較少的立體阻礙)用來製備POSS為主的奈米複合材料。此研究的第三章，我們共價接枝八個烷氧胺基團(N-alkoxyamine)到矽烷氧的笼狀立方體的八個端點(SiO1.5)8，做為八官能基起始劑製備星狀的聚苯乙烯[POSS-(PS)8]，聚苯乙烯及聚對位乙烯吡啶的嵌段式共聚物[POSS-(PS-b-P4VP)8]和聚苯乙烯及聚對位乙烯酚的嵌段式共聚物[POSS-(PS-b-PVPh)8]。和線性聚苯乙烯比較，動力學分析星狀的聚苯乙烯有相似的趨勢，指出從較少立體阻礙多官能起始的POSS可得到良好星狀高分子聚合的特性。 在此研究的第二章，雙親性的嵌段式共聚物(PCL-b-P4VP)可以從水相把HAuCl4的離子化合物轉移到有機相(dichloromethane)利用離子間作用力如[NH(AuCl)4]；借由NaBH4的環原及大量選擇性溶劑(insoluble P4VP blocks in toluene)，可經由嵌段式共聚物微胞穩定分散金奈米晶粒在有機溶劑中。然而，用嵌段式共聚物微胞包覆的金奈米晶粒會降低表面反應活性；因此使用較大體積的保護基團，可利用基團間的空隙讓反應物分子進入與產物分子出去，如此可維持奈米晶粒表面原子的高反應性。就已報導的POSS膠體晶體，POSS膠體先堆積而後再脫附溶劑分子造成，晶格常數a略大於POSS膠體的尺寸，意即POSS膠體的堆積的晶體固體會有空隙。在此研究的第四章，我們利用硫醇基POSS(SH-POSS)製備POSS和金奈米晶粒複合的奈米粒子(POSS-Au hybrid NPs)；當1.3奈米大小的硫醇基POSS吸附在約2奈米的金奈米晶粒表面，可預期會抑制硫醇基POSS的結晶，造成非結晶性的複合奈米粒子(POSS-Au hybrid NPs)。加入過量的硫醇基POSS，可利用硫醇基POSS的結晶做為模板將複合奈米粒子(POSS-Au hybrid NPs)組裝在模板的表面，構成很特別的蕨葉狀微結構。此研究，可發現POSS是很好的保護劑可以將金奈米晶粒分散在固態或溶液中。 鈀的奈米晶粒(Pd NCs)常用來做為碳碳鍵隅合的觸媒像Suzuik或Heck的反應，因此，我們所製備POSS和鈀奈米晶粒複合的奈米粒子(POSS-Pd hybrid NPs)，針對第二章的發現，硫醇基POSS晶體間的空隙可預期會有很好的觸媒活性。在此研究的第五章，我們發現一種不用化學環原劑的方法製備POSS和鈀奈米晶粒複合的奈米粒子(POSS-Pd hybrid NPs)，製備方法是把醋酸鈀和硫醇基POSS或十二烷基硫醇在甲苯溶劑中共沸，可以觀察到溶液從紅色的鈀離子錯合物轉變到黑色的鈀奈米晶粒。在此研究的第一章回顧金、銀、鈀和鉑奈米晶粒的製備方法，可分為化學環原法(chemical reduction)和熱溶劑法(solvothermal reduction)；所製備的鈀奈米晶粒(Pd NCs)可用做Heck碳碳鍵隅合丙烯酸甲酯(methyl acryalte)和碘基苯(iodobenzene)，與十二烷基硫醇保護的鈀奈米晶粒(C12-Pd hybrid NPs)比較，POSS和鈀奈米晶粒複合的奈米粒子(POSS-Pd hybrid NPs)有較好的化學反應特性。 此研究的第六章，我們總結四項重要的研究結果：(i) 低溫製備烷氧胺基(N-alkoxyamine)化合物做為氮氧化物為媒介自由基聚合；(ii) 活性自由基聚合星狀聚苯乙烯(star polystyrene)和其星狀-嵌段式共聚物；(iii) POSS結晶模板可用來自組裝POSS和金奈米晶粒複合的奈米粒子(POSS-Au hybrid NPs)，構成形狀特殊的蕨葉狀微結構和(iv) 低溫熱溶劑法環原製備POSS和鈀奈米晶粒複合的奈米粒子(POSS-Pd hybrid NPs)做為良好觸媒用在Heck隅合丙烯酸甲酯和碘基苯。

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.