Mechanism of thermal depolymerization of trimethylsiloxy‐terminated polydimethylsiloxane

Abstract “Catalyst‐free” trimethylsilyl end‐blocked polydimethylsiloxanes of M n = 68,300 and 111,000 were isothermally depolymerized above 400°C. The volatilized products were a mixture of cyclic oligomers and trace quantities of Me 3 Si(OSiMe 2 ) n OSiMe 3 ( n = 0,1). The relative degree of polymerization was followed as a function of fractional conversion. The data were consistent with the oretical curves for a mechanism involving initiation by random siloxane bond cleavage followed by a rapid and complete unzipping of the kinetically active fragments. It is suggested that catalysis may be responsible for the initiation process, thus accounting for the low activation energy (43 Kcal/mol) relative to the siloxane bond energy (108 kcal/mol).