An alternative method for the determination of siloxane activities toward basic equilibration catalysts

• Published in: Journal of the Serbian Chemical Society Vol. 70; no. 12; pp. 1461 - 1468
• Main Author: Govedarica, Milutin
• Format: Journal Article
• Language: English
• Published: Serbian Chemical Society 2005
• Subjects: activities of siloxanes; basic equilibration catalyst; siloxane equilibrations
• ISSN: 0352-5139; 1820-7421
• DOI: 10.2298/JSC0512461G

The method used is based on the well-known fact that siloxane equilibrates once formed, do not change their compositions unless some siloxane compound is added, in which case new equilibrium compositions appear. As these composition changes, as well as their dynamics, are caused solely because of the addition of a particular siloxane compound, they are expected to be specific, and should contain information about the siloxane activities toward the applied equilibration catalyst. It was shown that the viscosities of such systems, measured as a function of reaction times, could be used for the determination of the relative activities of siloxanes. Proceeding from this basic assumption, some commonly used siloxanes were tested in equilibrations catalyzed with tetramethylammonium hydroxide, TMAH. The siloxanes were hexamathylcyclotrisiloxane, D3, octamethylcyclotetrasiloxane, D4 tetravinyltetramethylcyclotetrasiloxane, D4Vinyl, hexamethyldisiloxane MM, and a linear all-methyl oligosiloxane of number average molecular weight of approximately 800.MD8.5M. The following decreasing order of activities toward the TMAH-catalyst was obtained: D3>MD8.5M>D4>D4Vinyl>MM. Koriscena metoda se zasniva na poznatoj cinjenici, da jednom formirani siloksanski ekvilibrati vise ne menjaju svoj sastav, osim ako im se doda neko siloksansko jedinjenje, u kom slucaju dolazi do stvaranja novog ravnoteznog sastava. Treba ocekivati da ova promena sastava, kao i dinamika promene - s obzirom da su izazvane iskljucivo dodatkom siloksanskog jedinjenja - budu specificne i da sadrze informacije o aktivnosti dodatog siloksanskog jedinjenja prema primenjenom katalizatoru ekvilibracije. Pokazano je da viskoziteti reakcionih smesa - mereni u zavisnosti od vremena trajanja reakcija - mogu da se iskoriste za odredjivanje relativnih aktivnosti siloksana. Polazeci od ove osnovne pretpostavke, ovom metodom odredjene su aktivnosti nekoliko siloksana, i to u bazno katalizovanim ekvilibracijama. Katalizator je bio tetrametilamonijum hidroksid, TMAH, a siloksani heksametilciklotrisiloksan, D3, oktametilciklotetrasiloksan, D4 tetraviniltetrametilciklotetrasiloksan, D4Vinyl, heksametildisiloksan, MM, i jedan linearni metil supstituisani oligosiloksan srednje brojne molarne mase od oko 800, MD8.5M. Dobijen je sledeci opadajuci redosled aktivnosti D3>MD8.5M>D4>D4Vinyl>MM.