頁籤選單縮合
題 名 | Kinetics of Polycyclotrimerization of Aromatic Dicyanates |
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作 者 | Lin,R. H.; Su,A. C.; Hong,J. L.; | 書刊名 | Journal of Polymer Research |
卷 期 | 4:4 1997.10[民86.10] |
頁 次 | 頁191-202 |
分類號 | 346.84 |
關鍵詞 | Polycyclotrimerization; 4,4-Thiodiphenylcyanate; Bisphenol-A dicyanate; Aromatic dicyanate; Autocatalysis; |
語 文 | 英文(English) |
英文摘要 | Polycyclotrimerization of 4,4'-thiodiphenycyanate(TDPC) and bisphenol-A dicyanate (BADC) were studied and compared by means of differential scanning calorimetry. Samples of different impurity levels(most likely residual moisture) or different catalyst loadings (n-nonylphenol) were studied. Moisture absorbed may indeed funcition as a catalyst. In the absence of residual phenols or added catalyst, the polycyclotrimerization of identical species shared the same apparent activation energy and all followed an autocatalyzed first-order rate expression. The autocatalytic effect was justified by the cure behavior of partially cured monofunctional cyanate (p-diphenyl cyanate). The rate expression obtained by the dynamic method is still available for the isothermal method. In the presence of an externally added catalyst (n-nonylphenol, NP), the polycyclo- trimerization proceeded at obviously lower temperature as compared with the uncatalyzed case. In addition to the expected lowering of activation energy ( independent of the catalyst concentration), the cure reaction exhibited an autocatalyzed higher order kinetics (second order for TDPC system and 1.7-th power for BADC system). These kinetic observations were explained in terms of proposed mechanistic scheme in which the competition between hydroxyl-catalyzed and autocatalytic paths is considered. In particular, formation of NP aggregates ((NP)�o, where m= 7 for TDPC system and m= 5 for BADC system, respectively) is proposed to explain the less-than-additive catalytic capacity with increasing added NP level. |
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