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通过裂解/色谱-质谱联用(Py/GC-MS)与热失重-质谱联用(TGA—DTA/MS)对耐高温纤维间位、对位芳香族聚酰胺(PMIA,PPTA)在惰性气体下的热分解过程进行分析。Py/GC—MS迅速升温得到的裂解产物与TGA-DTA/MS连续升温得到的降解产物有较好的对应,3步降解的PMIA与1步降解的PPTA在过程上的差异反映在不同阶段降解与裂解产物的区别上。通过水解、均裂等反应机制对二者不同的热分解进行解释:在低分解温度时,运用水解机制解释了PMIA纤维3步的失重过程和低的耐热性;而随着温度升高,均裂机制增强,使得PPTA纤维在1000℃时失重较PMIA高。 相似文献
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The C-I bond dissociation enthalpies (BDE) of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD(T) with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C(sp3)-I and C(sp2)-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted (iodomethyl)benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined. 相似文献
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取代基对木质素三聚体模型化合物醚键均裂反应影响的密度泛函理论研究 《燃料化学学报》2016,44(3):335-341
利用密度泛函理论M062X/6-31++G(d,p)方法,对27种具有不同取代基(甲基、羟甲基和甲氧基)的木质素三聚体模型化合物的Cα-O和Cβ-O键均裂解离能进行了理论计算,探究了不同位置取代基对醚键解离能的影响规律。结果表明,当R2或R3位氢原子仅有一个被甲氧基取代时,Cβ-O键解离能变化很小;当R2、R3位氢原子均被甲氧基取代时,Cβ-O键解离能明显降低;且R4、R5位甲氧基能强化R2、R3位甲氧基对Cβ-O键解离能的降低程度,而不受R1位取代基的影响。当R4、R5位氢原子相继被甲氧基取代时,Cα-O键解离能逐渐降低,且R2、R3位甲氧基也能强化R4、R5位甲氧基对Cα-O键解离能的降低程度。当R1位氢原子相继被甲基、羟甲基取代时,Cα-O键解离能逐渐升高,然而R2、R3位甲氧基会弱化R1位甲基、羟甲基对Cα-O键解离能的升高程度;R1位甲基不会影响Cβ-O键解离能,羟甲基却能明显提高Cβ-O键解离能。 相似文献
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The photodissociation mechanism of benzyl chloride (BzCl) under 248 nm has been investigated by the complete active space SCF (CASSCF) method by calculating the geometries of the ground (S0) and lower excited states, the vertical (Tv) and adiabatic (T0) excitation energies of the lower states, and the dissociation reaction pathways on the potential energy surfaces (PES) of SI, TI and T2 states. The calculated results clearly elucidated the photodissociation mechanism of BzCl, and indicated that the photodissociation on the PES of T1 state is the most favorable. 相似文献
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Saad Moulay Zakia Zeffouni 《高分子科学》2007,(3):297-302
PVC was subjected to a chemical modification aiming at replacing the chlorine atoms by pyridine groups via a homolytic route. Pyridine groups were peculiarly affixed to the PVC matrix via a carbon-carbon bond rather than a carbon-nitrogen one. PVC was first iodinated using the Conant-Finkelstein reaction, followed by the application of the homolytic conditions of Minisci to generate pyridinated PVC with a varying degree of substitution. The extent of substitution was not high; the reaction on 30% iodinated PVC afforded a degree of modification no greater than 3%. 相似文献
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