Kinetics of nonequilibrium methylsiloxane polymerization and rearrangement

Nonrandom reactions were demonstrated experimentally during the polymerization of (CH 3 ) 3 SiOSi(CH 3 ) 3 plus [(CH 3 ) 2 SiO] 4 and the rearrangement of (CH 3 ) 3 SiO[(CH 3 ) 2 SiO] 5 Si(CH 3 ) 3 or (CH 3 ) 3 SiO[(CH 3 ) 2 SiO] 8 Si(CH 3 ) 3 , using sulfuric acid‐treated Fuller's earth as catalyst. Cyclic and linear reaction products were analyzed by gas–liquid chromatography. A four‐step polymerization mechanism was proposed to account for the approach to equilibrium from either the forward or reverse direction. Reaction rate expressions for this mechanism were reduced to a finite set of nonlinear ordinary differential equations. These were solved by using a fourth‐order Runge‐Kutta numerical integration on a Burroughs B5500 computer. The calculated molecular weight distributions thus obtained were found to agree at all times with the distributions from polymerization and rearrangement experiments.