PYROLYSIS OF POLYOLEFIN ELASTOMERS
PYROLYSIS OF POLYOLEFIN ELASTOMERS
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DOI：
10.1002/pi.4980080402
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发表时间：
1976-01-01
期刊：
影响因子：
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通讯作者：
YOUREN, JW
中科院分区：
文献类型：
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作者：
SMITH, DA;YOUREN, JW
两种乙烯-丙烯三元聚合物（EPDM）、两种异丁烯-异戊二烯共聚物（IIR）、一种聚异丁烯（PIB）和一种氯磺化聚乙烯（CSPE）的商业样品在石英微炉中770 - 1370 K的温度下进行热解。挥发性产物通过气相色谱分析，使用宽沸点和高沸点柱，火焰电离检测器和/或在线四极杆质谱，以氦为载体。在交联聚苯乙烯柱上分离低分子量气体，并以氩气为载体，用卡塔罗-米进行检测。本文提出了热解产物产率的温度依赖性机制。在一次热解（约770 ~ 870 K）过程中，EPDM产物主要由1:5:9（13:17）的分子内氢转移产生，并伴有一定程度的解压缩。也有证据表明有少量的转移到第三个碳原子和一些β -裂变。IIR和PIB可能是通过逐步循环单分子消除产生异丁烯的。然而，一些其他产物，包括端粒、甲烷、异丁烷和新戊烷，可以用异丁烯的端粒化和随机分裂后的分子内转移反应来解释；在870k时，已经有一些芳香化的证据。CSPE热解由于SO2Cl基团的初步损失和脱氢氯化反应形成多烯而变得复杂。伴随交联可能涉及分子间HCl的消除和/或两个已经经历脱氢氯化的聚合物分子之间的Diels - Alder型反应。随后主链的热降解主要通过1:5的氢转移进行。在中等温度（900 K以上）发生二次热解，通过改良的Rice机制和相关的分子内循环解离，由一次热解形成的高alk - l -烯分解成低分子量产物。类似的机制也被用来解释IIR和CSPE的二次产物。在较高的温度下（1000 K以上），进一步发生碎裂、环化和芳香化。发生。所有聚合物的产氢率都急剧上升，而C3/ c4产物的产率则下降；c2产率在1100 K左右达到最大值。在1200k以下，苯的产率最高。甲苯的产率在1100 K以上下降，但萘的产率在增加中形成，在1220 K左右达到最大值。在这些较高的温度下，由于中等大小的分子消失，产物谱被简化，只留下小的碎片产物和相当大的多核芳烃（蒽等）。对于EPDM生成环产物和（特别是）高碳数甲基取代的正烯烃/烷烃的IIR -环化，提出了两种主要途径；中间分子如烯烃+二烯的Diels - Alder反应。在研究的最高温度下，高氢产率伴随着挥发性产物总产率的大幅下降，这是由于焦化反应中芳烃的进一步缩合。
Commercial samples of two ethylene—propylene terpolymers (EPDM), two isobutene— isoprene copolymers (IIR), one polyisobutene (PIB) and one chlorosulphonated polyethylene (CSPE) were pyrolysed at temperatures between 770 and 1370 K in a quartz micro‐furnace. Volatile products were analysed by gas chromatography using wide‐boiling‐range and high‐boiling‐point columns with flame ionisation detectors and/or online quadrupole mass spectrometry using helium as carrier. Low molecular weight gases were separated on a crosslinked polystyrene bead column and detected with a katharo‐meter using argon as carrier. Mechanisms are put forward to account for the temperature‐dependence of pyrolysis‐product yields as follows.In the primary pyrolysis (ca 770–870 K) EPDM products arise principally from 1 : 5 : 9(: 13 : 17) intramolecular hydrogen transfer accompanied by some unzipping. There is also evidence for a small amount of transfer to the third carbon atom and of some β‐scission. IIR and PIB yielded isobutene presumably by stepwise cyclic unimolecular elimination. However, a number of other products including telomers, methane, iso‐butane and neopentane are explained by telomerisation of isobutene and intramolecular transfer reactions following random scission; at 870 K, there is already evidence for some aromatisation. CSPE pyrolysis is complicated by preliminary loss of SO2Cl groups and dehydrochlorination to form a polyene. Concomitant crosslinking may involve inter‐molecular elimination of HCl and/or a Diels‐Alder type reaction between two polymer molecules which have already undergone dehydrochlorination. Subsequent thermal degradation of the main chain proceeds principally by 1 : 5 hydrogen transfer.At intermediate temperatures (above 900 K) secondary pyrolysis occurs in which higher alk‐l‐enes formed by primary pyrolysis break down to lower molecular weight products probably by a modified Rice mechanism and associated intramolecular cyclic dissociation. Similar mechanisms are proposed to explain the secondary products from IIR and CSPE.At higher temperatures (above 1000 K) further fragmentation, cyclisation and aromatisation. occur. For all the polymers, hydrogen yields increase sharply and yields of C3/C4products diminish; C2yields show maxima at temperatures about 1100 K. Below 1200 K, benzene is formed in largest yield. Toluene yields fall at temperatures above 1100 K, but naphthalene is formed in increasing yields up to a maximum at about 1220 K. At these higher temperatures, the product spectrum is simplified by the disappearance of molecules of intermediate size leaving only small fragmentation products and rather large polynuclear aromatics (anthracene, etc.).Two main routes are suggested for the formation of cyclic products from EPDM and IIR‐acyclisation of (particularly) methyl‐substituted n‐alkenes/alkanes of sufficiently high carbon number; andbthe reaction of intermediate molecules such as olefin + diene by a Diels‐Alder reaction.At the highest temperatures investigated, high hydrogen yields are accompanied by a substantial drop in total yield of volatilisable products and this is attributed to further condensation of aromatics in coking reactions.