Modification of polymethylhydrosiloxane by dehydrocoupling reactions catalyzed by transition metal complexes: Evidence for the preservation of linear siloxane structures

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• 作者：Ruzhi Zhang ; Zhengcheng Zhang ; Khalil Amine and Robert West
• 关键词：dehydrocoupling ; polymethylhydrosiloxane ; siloxane backbone cleavage ; transition metal complex catalysts
• 刊名：Silicon Chemistry
• 出版年：2005
• 出版时间：May 2005
• 年：2005
• 卷：2
• 期：5-6
• 页码：271-277
• 全文大小：823 KB

文摘

Polysiloxanes with pendant poly(ethylene oxide) side chains (4 were prepared by the dehydrocoupling reaction of poly(methylhydrosiloxane) (PMHS, 3 with 2-(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethoxy)ethanol (1 and poly(ethylene glycol) methyl ether (2 using a metal catalyst. Catalysts investigated were tin(II) 2-ethylhexanoate, Rh(Ph₃P)₃Cl, and Pd₂(dba)₃. The reaction of a cyclic siloxane, D₄H, with 1 catalyzed by Pd₂(dba)₃ was also carried out to synthesize siloxane 6. The polysiloxanes were characterized by 1H NMR, 29Si NMR, FT-IR, and GPC. 29Si NMR study of these comb-like polysiloxanes revealed that there is a significant difference in the structure of the siloxane polymers prepared depending upon the catalyst. M, D, and T units were observed when tin(II) was used as a catalyst, but only M and D units were detected when Rh(Ph₃P)₃Cl or Pd₂(dba)₃ was employed. Furthermore, M and T units are negligible for the cyclic siloxane 3 using Pd₂(dba)₃. A mechanism is proposed to account for these observations.