Browsing by Author "Sha, YA"

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Chemical modification of dicyclopentadiene-based epoxy resins to improve compatibility and thermal properties
(2001)
Hsiue, GH
;
Wei, HF
;
Shiao, SJ
;
Kuo, WJ
;
Sha, YA
A. series of siloxane-containing epoxy resins was obtained by curing dicyclopentadiene-containing epoxy DG with the silicon-containing curing agents TS, DS, and AS. Curing behavior was studied using DSC, and the activation energies of the DG curing reaction with curing agents TA, DS, and AS were found to be 59, 80, and 157 KJ/mol. Meanwhile, the curing reaction of DG with diamines was found to be a first-order reaction using Arrhenius plots. In addition, thermal stability and the weight loss behavior of the cured polymers were studied via TGA. The silicon-containing resins displayed higher weight loss temperatures and higher char yields than the silicon-free resin. The activation energies of degradation ranged from 108 to 206 KJ/mol. The morphology of the cured pieces were investigated using SEM. The DG/TS and DG/DS are more compatible between the epoxy and the curing agents than DG/AS. The limited oxygen index (LOI) values of 31 to 34 for the DG-based resin confirmed the effectiveness of silicon-containing epoxy resins as flame retardants. (C) 2001 Elsevier Science Ltd. All rights reserved.
Ferroelectric liquid crystalline polymers based on mesogens with halogen-containing terminal groups
(2003-01-01)
Sha, YA
;
Hsiue, GH
;
Chiu, CH
;
Jeng, RJ
;
Tai, HC
A new series of halogen-containing side chain ferroelectric liquid crystal polymers was synthesized. Mesophases were characterized by differential scanning calorimetry, polarizing optical microscopy. X-ray diffraction and molecular simulation. The behaviour of the liquid crystalline phase was investigated with variation of chiral centres. spacer units and grafted ratios. It was found that the thermal stability and temperature range of the chiral smectic C phase decreased with increasing length of the oligo-oxyethylene spacer. and decreasing mesogenic group content. The bulky substituent attached to the chiral centre reduces molecular packing in smectic liquid crystal phases, which disturbs the orientation of the side chain liquid crystal polymer. Furthermore, the influence of molecular structure on electro-optical properties of FLCPs has been studied by broad band dielectric spectroscopy (from 0.1 to 1 x 10(6) Hz).
Novel phosphorus-containing dicyclopentadiene-modified phenolic resins for flame-retardancy applications
(2001-01-10)
Hsiue, GH
;
Shiao, SJ
;
Wei, HF
;
Kuo, WJ
;
Sha, YA
2- [4-(2-hydroxyphenyl)tricyclo[5.2.1.0(2,6)]dec-8-yl]phenol (HPTCDP) were prepared from dicyclopentadiene (DCPD) and phenol via Friedel-Crafts alkylation. DCPD-containing phenolic resin (DPR) was also synthesized by incorporating the DCPD-containing monomer HPTCDP with formaldehyde. DPR was further modified by grafting the phosphate group. The phosphorylation was confirmed by a Fourier transform infrared, P-31-NMR spectroscopy, and an element analysis. The phosphorus content in the DPR could be successfully tailored to give values of 3.46 to 7.79 wt % by varying the feeding ratios of the phosphorus group. The thermal stabilities of the phosphorus-containing polymers were identified by differential scanning calorimeter and thermogravimetric analysis. The glass transition temperature values were decreased as the content of phosphorus increased. High char yield 39-47 wt % in thermogravimetric analysis evaluation and limiting oxygen index values of 27 to 34 were found for all the phosphorylated phenolic resins. Such properties make these polymers highly promising for flame-retardant applications. (C) 2000 John Wiley & Sons, Inc.
Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers
(2001-03-01)
Hsiue, GH
;
Sha, YA
;
Hsieh, SJ
;
Jeng, RJ
;
Kuo, WJ
A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.