COPOLYMERIZATION KINETICS OF A MODEL SILOXANE SYSTEM

Using Si-29 NMR, we monitor the copolymerization of trimethylethoxysil ane and dimethyldiethoxysilane (model compounds for more complex sol-g el copolymer systems) in a batch reactor. Under the chosen conditions, the extents of self- and cross-condensation reactions are readily det ermined. Using a nonideal polycondensation kinetic model, we show that the copolymerization rate coefficient for a pair of sites of differin g functionality is bounded by their homopolymerization rate coefficien ts, lying closer to the larger one. This reactivity pattern generates a heterogeneous monomer distribution in the copolymerization products. (C) 1997 John Wiley & Sons, Inc.