THERMAL ANALYSIS OF POLYDIMETHYLSILOXANES .I. THERMAL DEGRADATION IN CONTROLLED ATMOSPHERES
THERMAL ANALYSIS OF POLYDIMETHYLSILOXANES .I. THERMAL DEGRADATION IN CONTROLLED ATMOSPHERES
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DOI：
10.1002/pol.1969.160070308
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发表时间：
1969-01-01
期刊：
影响因子：
--
通讯作者：
KENDRICK, TC
中科院分区：
文献类型：
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作者：
THOMAS, TH;KENDRICK, TC
在受控气氛中对无催化剂的聚二甲基硅氧烷（PDMS）进行了热重分析（TGA），并对结果进行了动力学分析，从而能够分离和识别各种分解过程。热解聚的计算活化能为42 ± 3千卡/摩尔，而热氧化的表观活化能为30 ± 2千卡/摩尔。等温条件下降解研究中残留物的主要降解产物和分子量分布研究的定量分析表明，在真空中，PDMS组分通过随机引发的机制降解为环状二甲基硅氧烷和低分子量线性残留物，假设该机制涉及形成分子内环状四中心过渡态，然后是硅氧烷键重排。该机制是线性PDMS组分的基本性质，并且与分子量无关。通过对羟基封端的PDMS组分进行进一步等温研究观察到的分子量分布（MWD）变化表明，在低于解聚温度的真空中存在链延长过程。该过程的表观活化能为8.6 ± 1 kcal/mole，归因于末端羟基的分子间缩合。
Thermogravimetric analyses (TGA) of catalyst‐free polydimethylsiloxanes (PDMS) have been carried out in controlled atmospheres and a kinetic analysis of the results has enabled the various decomposition processes to be separated and identified. The calculated activation energy for thermal depolymerization is 42 ± 3 kcal/mole, while thermo‐oxidation has an apparent activation energy of 30 ± 2 kcal/mole. Quantitative analyses of the major degradation products and molecular weight distribution studies of the residues from degradation studies under isothermal conditions have shown thatin vacuo, PDMS fractions depolymerize to cyclic dimethylsiloxanes and low molecular weight linear residues by a randomly initiated mechanism which, it is postulated, involves the formation of an intramolecular, cyclic, four‐centered transition state followed by siloxane bond rearrangement. This mechanism is a basic property of linear PDMS fractions and is independent of molecular weight. Molecular weight distribution (MWD) changes observed from further isothermal investigations on hydroxy endblocked PDMS fractions, have shown the presence of a chain‐lengthening processin vacuobelow the depolymerization temperature. This process, with an apparent activation energy of 8.6 ± 1 kcal/mole, is attributed to the intermolecular condensation of terminal hydroxyl groups.