Polycondensation Kinetics: 2. Time-Dependent29Si NMR Spectra of Poly-Dimethyldimethoxysilane

The polycondensation of dimethyldimethoxysilane has been studied by 29 Si NMR to high degrees of conversion at pH 2.8. The relative concentrations of nonbonded Si atoms ( D 0 ) and bound by one ( D 1 ) and two ( D 2 ) Si–O–Si bonds have been determined from the integrated intensities of the multiplets assigned to them. The measurement results have been considered in terms of the kinetic scheme proposed in the first paper. It has been found that the D 0 ( t ), D 1 ( t ), and D 2 ( t ) curves coincide with those measured for the ratio of the constants of competing processes of aggregation and addition of monomers k ≈ 0.15. The time-dependent molecular mass distributions have been determined with allowance for chain termination during the formation of cyclic and entangled oligomers.