| 摘要: | 有機過氧化物 (R-O-O-R’) 常用於高分子工業，以作為聚合反應之起始劑或聚合材料的交聯劑，亦可看成過氧化氫 (H-O-O-H) 的衍生物。有機過氧化物因含較弱的 O-O 鍵，易分解、易燃、易爆，對熱、震動、摩擦極為敏感，在製程或儲存過程中，若發生一些非預期因素造成製程偏離，如蓄熱、受熱或微量不相容物 (如:強酸、鹼，有機化合物或金屬離子) 時，會劇烈放熱並導致分解和熱失控反應。在國內、外也常發生因使用有機過氧化物導致火災爆炸的事故。二烷基過氧化物是市售中對熱最穩定的有機過氧化物，因能生成活性的烷氧自由基會捕捉聚合物主鏈上的氫原子，並引發聚合物分子間的化學反應，除在工業界上被廣泛的使用外，也適合用於研究不同取代基對有機過氧化物的熱、動力學影響。過氧化三級丁基 (DTBP) 雖是最穩定的二烷基過氧化物之一，又是公認的標準參考物質，也曾發生洩漏造成大火；而過氧化二異丙苯 (DCPO) 在國內也曾發生因在製程中加錯催化劑發生熱失控反應導致反應器爆炸。本研究使用微差掃描熱卡計(DSC) 和熱分析軟體 For K 對結構相似的四種二烷基過氧化物(如: 過氧化三級丁基 (DTBP)、過氧化異戊基 (DAPO)、過氧化三級丁基異丙苯 (TBCP) 和過氧化二異丙苯 (DCPO) 等)進行熱危害分析。以DTBP 為本研究的標準參考樣品，探討(一) 二烷基有機過氧化物熱分解模式(以DTBP為例)；(二) 不同升溫速率對DTBP和 DCPO熱、動力學的影響；(三) 不同取代基對二烷基過氧化物的熱、動力學參數之影響。研究結果顯示，DTBP 為兩階段的熱分解行為 (Stage：A→B1→B)；增加升溫速率會增加 DTBP 和 DCPO 的 外插起始放熱溫度 (Ts)、波峰溫度 (Tp)，和微增加起始放熱溫度 (To)，但對分解熱 (?H)、活化能 (Ea) 和頻率因子 (A) 則影響不大。四種二烷基過氧化物的平均頻率因子 (log A) 為14.3±1.1 s-1 和由ab initio計算所得之建議值 logA(s-1) =14 非常接近，可確認二烷基有機過氧化物自由基的主要分解路徑為 β – scission 斷鍵。由 To 值可知，二烷基有機過氧化物的熱穩定性分別是：DCPO < DAPO < DTBP 和DCPO < TBCP。由For K 和 AKTS 軟體所求得的 DTBP 之 TMRad 值(到達最大放熱速率時間) 相當接近。
Organic peroxides (ROO-R ') are commonly used in the polymer industry as an initiator for polymerization or a crosslinking agent for polymeric materials and are regarded as the derivatives of hydrogen peroxide (HOOH). Organic peroxide is characterized by the presence of a weak oxygen–oxygen bond (–O–O–) in the molecule resulting in easily decomposed, flammable, and exposable characteristics, making it very sensitive to heat, shock, friction, etc. During the manufacturing process or storage process, if some unexpected process deviation such as heat accumulated, heat or incompatible trace (such as acid, alkali, organic compound or metal ion) occurred, there will be a severe exothermic heat, resulting in decomposition and thermal runaway reactions. Incidents of fires or explosions caused by thermal decompositions of organic peroxides have occurred globally. Dialkyl peroxides (or di-tertiary alkyl) are among the most stable of all the commercially available organic peroxides. When subjected to heat, dialkyl peroxides decompose and generate a pair of alkoxyl radicals, which can initiate the desired reaction. Their stable alkoxy radicals have drawn lots of attention and have been studied by many researchers for their thermal kinetic decomposition behaviors. Although di-tertiary butyl peroxide (DTBP) is one of the most stable dialkyl peroxide and is also recognized as a standard reference material, it has caused a fire due to leakage. In Taiwan, dicumyl peroxide (DCPO) had caused a thermal runaway explosion of a reactor due to a mistaken addition of the catalyst in the manufacturing process. In this study, DSC and a thermal analysis software (For K) were used to study thermal hazards of four dialkyl peroxides (such as di-terbutyl peroxide (DTBP), di-amyl peroxide (DAPO), tertiary butyl cumyl peroxide (TBCP) and dicumyl peroxide (DCPO), etc.). DTBP was used as a standard reference sample in this study to investigate (i) The thermal decomposition mode of dialkyl peroxides (with DTBP as an example); (ii) The effect of heating rate on thermal kinetics of both DTBP and DCPO; (iii) The effect of different substituents on the thermal kinetics of the four dialkyl peroxides.The results show that thermal decomposition behavior of DTBP is a two-stage reaction (Stage: A → B1 → B); Increases in heating rate increases extrapolated onset temperature (Ts), the peak temperature (Tp), and only increases the onset temperature (To) by a little. However, increases in heating rate shows little or no effect on decomposition heat (ΔH), activation energy (Ea) and frequency factor (A) for both DTBP and DCPO. Dialkyl peroxides possessed an average eigenvalue of log A at about 14.3 ± 1.1. This is closely in agreement with log A = 14, which is a common pre-exponential factor for b C–C bond scission rate constant of all alkoxy radicals studied by Fittschen et al.. According to To, the ranking of thermal stability on dialkyl peroxides is determined to be in the following sequence: DCPO < DAPO < DTBP and DCPO < TBCP. Finally, the time to maximum rate (TMRad) of DTBP obtained from both For K and AKTS softwares are fairly close. |
