(I) Preparation and Characterization of Low Dielectric Constant Poly(silsesquioxanes) and Their Nanoporous Derivatives (II) New Environment-Responsive Polymers and Their Application on Sensoring of DNA and Zinc Molecules
Date Issued
2005
Date
2005
Author(s)
Yang, Chang-Chung
DOI
en-US
Abstract
In the first part of this thesis, the structural transformation of poly(silsesquioxanes) materials and the preparation of their nanoporous derivatives were investigated. Poly(silsesquioxanes) and their nanoporous derivatives with dielectric constant (k) less than 2.0 have become a new class of low k materials for advanced integrated circuits (IC). However, the structure and properties of poly(silsesquioxanes) during curing have not been addressed yet and the control of pore morphology of nanoporous poly(silsesquioxanes) through the composition or architecture of the amphiphilic block copolymers (ABCs) requires further exploration to obtain materials with medium porosity and closed-cell nanopores. To achieve the above goal, the structures and properties of poly(silsesquioxanes) films produced by curing were studied in the temperature range of 2400 to 3400C and the templating approach of ABCs was investigated for preparing low k nanoporous film. The methyl silsesquioxane (MSSQ) precursor and poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) or poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) were used as the matrix and templating agent, respectively. The ABCs with controllable molecular weight, distribution and architecture were prepared by living anionic polymerization. The effects of various architectures, molecular structures and compositions were investigated. A methodology on controlling the pore structure and properties of nanoporous films by ABCs as templates was proposed in this study.
The experimental results of the hydrogen silsesquioxane (HSQ) curing show that the transformation of the cage structure to the network structure is the major reaction in the temperature range of 240 to 3400C. The cage/network transformation can be explained by two-stage zero order kinetics. The rate constant of the first stage is 10-35 times more than that of the second stage. The difference is probably because the network structure of the second stage limits the structural transformation and results in a small frequency factor. The porosity of the cured HSQ films increases rapidly with curing times in the first 10 minutes and then reaches at a steady value. The evolution of porosity is probably due to the outgassing of the reaction side-product (SiH4), the trapped solvent (4-methyl-pentan-2-one) or the cage/network transformation.
Low dielectric constant nanoporous poly(methyl silsesquioxane) (PMSSQ) was prepared through the templating of ABCs. The experimental and theoretical studies suggest that the intermolecular hydrogen bonding interaction is existed between the PMSSQ precursor and PS-b-P2VP. The miscible hybrid and the narrow thermal decomposition of the PS-b-P2VP lead to nanopores in the prepared films from the results of transmission electronic microscopy (TEM), atomic force microscopy (AFM), and small angle X-ray scattering (SAXS). The effects of the loading ratio and the PS block volume ratio (fPS) were investigated. The AFM and TEM studies suggest that the uniform pore morphology should be prepared from a modest porogen loading level for the optimum intermolecular hydrogen bonding. The refractive index and dielectric constant of the prepared nanoporous films could be tuned by the loading ratio in the range of 1.361–1.139 and 2.359–1.509, respectively. The linear and star-shaped PS-b-P2VP all gave a well-dispersive pore structures while the repulsive interaction between cured hydrophobic PMSSQ and PS-b-P4VP led to a worm-like morphology. This study demonstrates the control of the morphology and properties of the nanoporous films through the polymer structure.
In the second part of this thesis, several environment-stimuli polymers were prepared and the pH, solvent polarity, temperature and zinc or DNA responsive UV-Vis and fluorescence spectral were characterized. The fluorescence-based sensoring materials are of importance for the visualization of target molecules in biological environments. Though many organic compounds of the fluorene- or benzoxazole-derivatives have been reported, nearly no paper reports the study of the environmental stimuli using the polymers containing the fluorene or benzoxazole. To achieve the above goal, the poly(N-isopropylacrylamide) copolymers containing the fluorene or benzoxazole moieties and several novel two-photon dye materials including polymers and small molecules were prepared and characterized. The effect of the pi-conjugation length and substitution position were investigated through the molecular design. The experimental results disclosed the fluorescence intensity of the target molecules could be enhanced due to the coordination with metal cations or in the basic condition. The interrupted ESIPT character of the HBO gave the possibility of metal sensoring. The longer pi-conjugation length led to a larger two-photon fluorescence and well-designed substitution position gave the character of hydroxyphenyl benzoxazoles which could be the candidate of novel two-photon dyes with metal sensoring ability.
Subjects
聚倍半矽氧烷
奈米孔洞材料
活性陰離子聚合法
雙光子
金屬檢測
amphiphilic block copolymer
silsesquioxane
nanoporous material
living anionic polymerization
environment-stimuli polymers
two photon
metal sensoring
Type
thesis