Browsing by Author "Hsieh, TH"

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Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups
(1997-09-30)
Hsu, CS
;
Chu, PH
;
Chang, HL
;
Hsieh, TH
;
交大名義發表
The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyl oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an Sd phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. (C) 1997 John Wiley & Sons Inc.
Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups
(1997-09-30)
Hsu, CS
;
Chu, PH
;
Chang, HL
;
Hsieh, TH
;
應用化學系
The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyl oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an Sd phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. (C) 1997 John Wiley & Sons Inc.
Simultaneous preparation of PI/POSS semi-IPN nanocomposites
(2006-03-24)
Chen, WY
;
Ko, SH
;
Hsieh, TH
;
Chang, FC
;
Wang, YZ
This investigation presents a simultaneous and convenient approach to produce a high-performance polyimide with a low dielectric constant by introducing the octa-acrylated polyhedral oligomeric silsesquioxane (methacrylated-POSS) into a polyimide matrix to form polyimide semi-interpenetrating polymer network (semi-IPN) nanocomposites. The differential scanning calorimetry (DSC) and Fourier-transform infrared (FT-IR) results indicate that the self-curing of methacrylated-POSS and the imidization of polyamic acid (PAA) occurs simultaneously. The morphology of a semi-IPN structure of polyimide[POSS-PI/POSS nanocomposites with POSS nanoparticles embedded inside the matrix is elucidated. The POSS particles are uniform and are aggregated to a size of approximately 50-60 nm inside the polyimide matrix. The interconnected POSS particles are observed at high POSS content. The structure is highly crosslinked, so the PI/POSS nanocomposites have an enhanced glass transition temperature. The high porosity of the PI/POSS nanocomposites markedly reduces the dielectric constant of PI because of the nanometer-scale porous structure of POSS.