Polysiloxanol condensation and disproportionation in the presence of a superacid

被引:12
作者
Grzelka, A [1 ]
Chojnowski, J [1 ]
Cypryk, M [1 ]
Fortuniak, W [1 ]
Hupfield, PC [1 ]
Taylor, RG [1 ]
机构
[1] Polish Acad Sci, Ctr Mol & Macromol Studies, PL-90363 Lodz, Poland
关键词
silanols; polysiloxanes; silanol polycondensation; siloxanol disproportionation; superacid;
D O I
10.1016/j.jorganchem.2003.11.029
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Kinetics studies of the condensation of model hydroxyl-terminated oligosiloxanes, pentamethyldisiloxane-1-ol (MDH) and heptamethyltrisiloxane-1-ol (MD2H), catalysed by protic complex of tetrakis(pentafluorophenyl)borate in the toluene solution were performed. The dominating reaction was condensation, which was accompanied by disproportionation of oligosiloxanols. Water released in the condensation forms separate dispersed phase, but the phase separation and the presence of water does not affect the rate of the polycondensation. Both processes, condensation and disproportionation, show analogous kinetic laws being first order in silanol and half order in catalyst. They exhibit also similar values of activation parameters. The kinetics are explained by the formation of a reactive protic complex of silanol with borate being in fast preequilibrium. with an unreactive complex including two borate molecules and the silanol molecules. The equilibrium lies to the side of the unreactive borate complex. (C) 2003 Elsevier B.V. All rights reserved.
引用
收藏
页码:705 / 713
页数:9
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