Date of Degree

9-2015

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Michal Kruk

Subject Categories

Chemistry | Polymer Chemistry

Abstract

The research work in this dissertation covers the synthesis of mesoporous organosilicas and (organo)silica/polymer nanocomposites. The content can be divided into 4 parts (8 chapters).

The first part of the dissertation is the introduction, which covers the background and progress in the field of mesoporous silicas, periodic mesoporous organosilicas and related inorganic/polymer nanocomposites. The second part of the dissertation (Chapter 2-5) involves the synthesis of mesoporous organosilicas from different organosilane precursors at mild acid concentration (0.1 M HCl) and low temperature (0 or 7 ℃) using Pluronic F127 (EO106PO70EO106) as a surfactant template. Chapter 2 focused on the synthesis of large-pore periodic mesoporous organosilicas (PMOs) with ethylene bridging groups using 1,2-bis(triethoxysilyl)ethane (BTEE) and 1,2-bis(trimethoxysilyl)ethane (BTME) as well as phenylene- bridged PMOs using 1,4-bis(triethoxysilyl)benzene (BTEB). The use of different micelle swelling agents was also discussed. The resulting PMOs in many cases had face-centered cubic structure with large pore diameters, pore volumes and unit-cell parameters. In Chapter 3, the synthesis of large-pore ethenylene (-CH=CH-) bridged PMOs with tunable pore sizes and face-centered cubic structures (Fm3m symmetry) using 1,2-bis(triethoxysilyl)ethylene (BTEEn) was discussed. The unit-cell parameters were tuned from 27 to 40 nm and the pore diameters were tuned from 13 to 22 nm by carefully adjusting the amount of swelling agent in the reaction mixture. Chapter 4 covered the synthesis of biphenylene-bridged PMOs using 4,4'-bis(triethoxysilyl)-1,1'-biphenyl (BTEBP) under the above mentioned conditions. The resulting materials had an ordered structure with pore diameters around 8.5 nm. Because of the presence of large aromatic groups in the framework precursor, the materials display a high molecular scale periodicity, which may contribute to the unique sheet type particle morphology. Chapter 5 discussed the synthesis of mesoporous organosilicas with pendant methyl groups using methyltriethoxysilane (MTES) as an organosilica precursor. These organosilicas have one methyl group attached to each silicon atom. The organosilicas have the pore diameters around 10 nm with cylindrical pores arranged in two-dimensional (2-D) hexagonal structure. The mesoporous organosilicas with accessible pores (through framework micropores) were thermally converted to closed-pore mesoporous organosilicas, without any degradation (or with minor degradation) of methyl groups. The closed-pore mesoporous organosilica materials usually have low dielectric constant, and so if a similar pore closing without organic group degradation can be accomplished for materials in a thin-film form, the resulting materials could be very useful in electronics industry.

The third part of the dissertation covers the synthesis of inorganic/polymer nanocomposites. In Chapter 6, poly(N-isopropylacrylamide) (PNIPAAm) brushes were grafted on the surface of large-pore methylene-bridged periodic mesoporous organosilica using surface-initiated activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The loading of the polymer can be controlled over a wide range by changing the polymerization time. A high loading of polymer (up to ~35 wt. %) was achieved without the mesopore blocking. This research demonstrates that the range of ordered mesoporous materials suitable as supports for polymer brushes extends beyond pure-silica materials into hybrid organic-inorganic frameworks. In Chapter 7, poly(2-(2'-methoxyethoxy)ethyl methacrylate) (PMEO2MA), poly(oligo(ethylene glycol) methacrylate) (Mn=300 g/mol) (PMEO5MA) and P(MEO2MA-co-MEO5MA) brushes were grafted on the surface of ultra-large-pore SBA-15 silica using ARGET ATRP. It was seen that loading of the polymer can be controlled over a wide range by changing the polymerization time. High loading of polymer (up to ~34 wt.%) was achieved without the pore blocking.

The last part of the dissertation (Chapter 8) covers the conclusions from all the chapters.

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