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Syntheses and Properties of Novel Epoxy Curing Agents and Benzoxazine
Xiong, Tsai Sheng
A novel phosphorus-containing tri-functional novolac (dopotriol) was synthesized from the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenan threne 10-oxide (dopo) and rosolic acid. The structure of dopotriol was confirmed by NMR spectrum and elemental analyses. The dopotriol was blended with phenol novolac (PN) in the ratio of 10/0, 8/2, 6/4, 4/6, 2/8 and 0/10 to serve as curing agents for diglycidyl ether of bisphenol A (dgeba). Thermal properties such as Tg, thermal decomposition temperature, flame retardancy, moisture absorption and dielectric properties of cured epoxy resins were evaluated. The activity and activation energy of curing were studied using the methods of the Kissinger and Ozawa by dynamic DSC scans. The glass transition temperatures of cured epoxy resins are in the range of 138-159 oC, increasing with the phosphorus content. This is rarely seen in the literature after introducing a flame retardant element. The flame retardancy increases with phosphorus content and a UL-94 V-0 grade can be achieved with phosphorus content of 1.87%. Similar dielectric properties and moisture absorption were observed for these phosphorus-containing epoxy resins, implying that the introduction of phosphorus into epoxy does not affect the dielectric properties and moisture absorption.
We also synthesized another novel phosphorus-containing triamine (dopo-ta) from the nucleophilic addition of 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (dopo) and pararoaniline chloride using triethylamine as a catalyst. We confirmed the structure of dopo-ta by IR, Mass, NMR spectrum and elemental analysis. The dopo-ta was served as a curing agent for diglycidyl ether of bisphenol A (dgeba) and dicyclopentadiene epoxy (hp7200). Properties such as glass transition temperature, thermal decomposition temperature, flame retardancy, moisture absorption and dielectric properties of cured epoxy resins were evaluated. The glass transition temperatures of cured dgeba/dopo-ta and hp7200/dopo-ta are 171 oC and 190oC, respectively. The flame retardancy increases with the phosphorus content and a UL-94 V-0 grade can be achieved with a phosphorus content of 1.80 wt % for dgeba/dopo-ta/ddm and 1.46 wt % for hp7200/dopo-ta/ddm systems. The dielectric constant for dgeba/dopo-ta and hp7200/dopo-ta is 3.00 and 2.89, respectively, implying dopo-ta curing system exhibits low dielectric properties.
A trifunctional benzoxazine, dopot-m and CH3t-m, was prepared from dopotriol and 1,1,1-Tris(4-hydroxyphenyl)ethane, and their structure were confirmed by NMR and IR spectra, etc. The synthesized benzoxazines were blended with another benzoxazine based on 4,4'-dihydroxydiphenylmethane (F-a) in the different ratios. Glass transition and thermal degradation behaviors of these thermosets were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The materials exhibited high glass transition temperatures and thermal decomposition temperature. V-0 materials were obtained when dopot-m/F-a were tested for ignition resistance with the UL-94 test.
我們經由dopo與rosolic加成反應合成新穎的三官能含磷硬化劑dopotriol，其結構經由NMR、EA等分析確認無誤。dopotriol與PN以比例10/0, 8/2, 6/4, 4/6, 2/8 and 0/10做為dgeba硬化劑。我們測得硬化環氧樹脂的熱性質Tg、Td、燃燒性、吸水性和電氣性，而硬化活化能使用DSC經由Kissinger與Ozawa估計，硬化的環氧樹脂Tg在138oC~159oC之間，隨磷含量增加，這在文獻中導入難燃元素是少見的。另外難燃性隨磷含量增加在1.87%達UL-94 V-0等級。結果顯示介電質與吸水率顯示不受導入磷的影響。
另外，我們也將dopo與pararoaniline chloride使用triethyl amine做觸媒，合成了含磷六官能的dopo-ta。我們藉由IR、NMR、Mass與EA分析。我們將dopo-ta做為dgeba和hp7200的硬化劑，並測得其硬化後的Tg、Td、難燃性、吸水性與電氣性。硬化後的dgeba/dopo-ta和hp7200/dopo-ta，Tg分別為171oC與190oC。難燃性隨磷含量增加，對dgeba/dopo-ta/ddm與hp7200/dopo-ta/ddm磷含量分別在1.80wt%與1.46wt%可達UL-94 V-0等級。介電常數分別為3.00與2.89顯示dopo-ta硬化系統有低介電性質。
由三官能的dopotriol與1,1,1-Tris(4-hydroxyphenyl)ethane製造出的benzoxazine經由NMR和IR等鑑定其結構。合成出的benzoxazine再與另一4,4’-dihydroxydiphenylmethane型的benzoxazine (F-a)以不同莫耳比例混合，並藉由DSC與TGA測其硬化後的熱性質，此混掺的材料顯示有不錯的玻璃轉化溫度與熱裂解溫度。而藉由UL-94 測試，我們確定dopot-m有難燃效果。
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