多面體寡聚倍半矽氧烷奈米複合材料之合成與特性及其微結構研究

Synthesis and Characterization of Polyhedral Oligomeric Silsesquioxane Based Nanocomposites and Their Microstructures

林威戎(Wei-jung Lin)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/博士(2004年)

https://doi.org/10.6342/NTU.2004.00476

摘要

近年來，多面體寡聚倍半矽氧烷(POSS)受到了廣泛的研究並且開啟了新的奈米複合材料合成途徑。POSS因具有無機的核心及有機的鏈段，可以以奈米等級有效地分散在混成材料中，此外其特殊立體結構及耐熱性，更增添其應用上的多樣性，本文在簡介部分詳細整理了相關的POSS文獻，包括POSS的合成方法、POSS與各種高分子的混成材料製備及應用。在本研究中，以POSS衍生物出發，分別探討POSS與共軛發光高分子形成之星狀結構對發光性質之影響，以電腦模擬POSS自身反應所形成之孔洞結構，及POSS與聚醯亞胺混成材料在作為光學薄膜或低介電常數薄膜的性質與應用。

本文第一部份研究POSS對共軛發光高分子之發光及耐熱特性之影響。首先合成末端含溴苯基之POSS，並與高分子polyfluorene (PFO)以鎳催化反應得到以POSS為核心之星狀共軛發光高分子，結果顯示POSS的加入明顯降低聚集的產生並加強其耐熱性，研究發現POSS會阻礙玻璃轉移及結晶行為，且在不同溶劑中或在固態下對可見光之吸收可發現聚集產生之吸收隨POSS加入而減少，相對於原本純高分子產生明顯之綠光，加入POSS後發光熱穩定性可增加至150度。另外將此材料製備成單層發光二極體元件，其最大亮度及發光效率相較於純高分子可增加兩倍，因此，藉由加入無機之POSS可提供一新的途徑使共軛發光高分子獲得更佳之耐熱及光電性質。

本文第二部份則以連續體分子模型及蒙地卡羅法模擬POSS奈米複合材料之網狀孔洞結構，此模擬清楚地分辨出奈米孔洞結構中所包含較小的分子間孔洞及較大的微孔洞，因此藉由觀察交聯程度、孔洞大小及分佈來探討與POSS上鏈段長度、鏈段硬度及可交聯鏈段數目之關係。模擬結果顯示交聯程度及分子間孔洞的大小隨POSS上鏈段長度增加增加，而微孔洞的大小卻隨著鏈段長度增加而趨減小，結果均與實驗相符合。硬鏈段的POSS則因含有較多的自由未反應鏈段，導致較低的交聯程度與較窄的孔洞分佈，相反地，減少可以反應的鏈段數目並未影響反應交聯程度，卻使得分子間孔洞大小增加，也使得POSS包含了更大的體積並均勻地分散在系統內，降低了產生大型微孔洞的機率，因此，藉由電腦模擬的輔助可以觀察到實驗無法觀察到的結果並預測不同條件所產生對POSS為結構的影響。

本文第三部份則是合成寡聚甲基倍半矽氧烷(O-MSSQ)與聚醯亞胺(polyimide)混成材料，此奈米級O-MSSQ可提供無機含量精確控制，研究有機-無機組成、混成結構對此材料製備成為薄膜後之型態及特性的影響。相分離可以藉由控制聚醯亞胺的分子量及O-MSSQ的Si-OH反應基含量得以改善，因此低分子量聚醯亞胺並配合使用偶合劑可得到均勻透明的薄膜，抑或使用含大量反應基之O-MSSQ。熱性質及機械性質在無機成分加入後有顯著的提升，並且可以利用有機-無機比料調控的折射率及介電常數，此外雙折射率也相對地減低，因此，本研究顯示此混成材料可作為光學薄膜或低介電常數薄膜的應用。

由前述研究可發現奈米複合材料的結構與性質可經由POSS的加入得到明顯改進，後續的研究包括藉由理論與實驗精確地控制POSS奈米複合材料的結構、型態與性質。

關鍵字

倍半矽氧烷 ； 共軛高分子 ； 聚醯亞胺 ； 蒙地卡羅

並列摘要

Polyhedral oligomeric silsesquioxane (POSS) based nanocomposites have been extensively studied recently. The inorganic core and organic tethers enable POSS to disperse homogeneously in hybrid materials. Their special stereo structure and thermal stability also increase the versatile applications of the POSS based nanocomposites. However, the details on the correlation between the structure, morphology and properties require further exploration. In this study, the structures and properties of three POSS based nanocomposites were explored: (1) synthesis of new POSS core and its star-like polyfluorene derivative to address the effect of POSS on the morphology and properties of nanocomposites; (2) The theoretical network structure of the POSS simulated by Monte Carlo method; (3) Polyimide/POSS nanocomposites synthesized from oligomeric silsesquioxane precursor solutions.

In Chapter 2, a novel starlike polyfluorene derivative, PFO-SQ, was synthesized by the Ni(0)-catalyzed reaction of octa(2-(4-bromophenyl)ethyl)octasilsesquioxane (OBPE-SQ) and polydioctylfluoroene (PFO). The incorporation of the silsesquioxane core into polyfluorene could significantly reduce the aggregation as well as enhance the thermal stability. The DSC study showed an elimination of the glass transition and the crystallization as well as a significant reduction on the melting enthalpy in the PFO-SQ. The UV-Vis absorption spectra in a different solvent combination or solid state film showed an intensity reduction of the aggregation peak for the PFO-SQ in comparison with that of the PFO. The stability of the photoluminescence spectra of the PFO-SQ could be up to 1500C while that of the PFO showed a significant green emission. A single-layer LED device using the PFO-SQ showed a turn on voltage of 6.0 V, a brightness of 5430 cd/m2 (at a drive voltage of 8.8 V), and a current density of 0.844 A/cm2. The maximum luminescence intensity and quantum efficiency of the PFO-SQ were almost twice as good as those of the PFO electroluminescent device. Hence, the incorporation of the inorganic silsesquioxane core into polyfluorenes could provide a new methodology for preparing organic light-emitting diodes with improved thermal and optoelectronic characteristics.

In chapter 3, the network structures of POSS based nanocomposites are studied by continuous-space Monte Carlo simulations. The nanoporous network contains intercubic pores and mesopores which can be clearly identified in this work. In terms of degree of crosslinking and pore size distribution (PSD), effects of linker length, tether rigidity and number of reactive tethers are examined. It is found that the extent of crosslinking as well as the intercubic pore size of the network increases as linker length increases which are consistent with experimental findings. However, the mesopores appear to shift to a smaller radii regime for networks with longer linkers. Networks with rigid tethers contain lots of free linkers, thus, low crosslinking density and narrow PSD are observed. On the other hand, reduction of the reactive tethers shows an insignificant effect on the degree of crosslinking of the system. The fact that the intercubic pore size increases as the number of reactive tethers decreases causes the nano-building blocks to possess larger free volumes and distribute themselves more evenly through out the system. As a result, it reduces the possibility of forming large mesopores.

In the final part of this study, polyimide/silsesquioxane hybrid materials were synthesized by the aminoalkoxysilane-capped poly(pyromellitic dianhydride-co-4,4’- oxydianiline)(amic aicd) and oligomeric methylsilsesquioxane (O-MSSQ) precursor. The O-MSSQ moiety was used for obtaining the precise nano-inorganic moiety in the hybrid materials. The effects of molecular structures and composition on the morphologies and properties of the prepared hybrid materials were studied. The phase separation of the prepared hybrid materials could be controlled by the molecular weight of the polyimide moiety, the Si-OH end group content of the O-MSSQ or the coupling agent. Homogeneous and transparent hybrid thin films were obtained from the case of low molecular weight polyimide moiety with a coupling agent, 3-aminopropyltrimethoxysilane (APrTMS). However, micro-phase separation was occurred if the molecular weight of the polyimide moiety enhanced or without a coupling agent, as evidenced by AFM, FE-SEM, and ESCA. The high Si-OH content of the O-MSSQ could enhance the bonding density between the organic and inorganic moiety and thus retard phase separation. The thermal and mechanical properties of the prepared hybrid materials were largely improved from the parent polyimide, PMDA-ODA, which were demonstrated by the TGA, DSC, and thermal-stress analysis. The hybrid materials showed adjustable refractive index and dielectric constant by varying the O-MSSQ content. The birefringence of the PMDA-ODA was reduced by incorporating the O-MSSQ moiety. This work revealed that the polyimide/O-MSSQ hybrid materials could have potential applications as optical films or low dielectric constant materials.

The above studies suggest that the structure and properties of nanocomposites could be significantly improved through the incorporation of well-defined POSS structure. Ongoing work will be the precise control of the structure, morphology, and properties of POSS based nanocomposites through the experimental and theoretical approach.

並列關鍵字

Monte Carlo ； silsesequioxane ； conjugated polymer ； polyimide

參考文獻

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