Kinetic, structural, and reaction engineering studies of inorganic-organic sol-gel copolymers

This work describes quantitative modeling of the kinetics of structure development during polymerization of alkoxysilanes. The modeling includes both deterministic chemical kinetics and stochastic simulation. Polycondensation is experimentally monitored mainly by 29Si nuclear magnetic resonance (NMR).;For hydrolysis and polycondensation of (poly)methyl (poly)ethoxysilanes in homogeneous solution, three necessary modeling features are identified: (1) hydrolysis reversibility and rapidness leading to pseudoequilibrium, (2) condensation reactivity decreasing strongly as connectivity increases, and (3) extensive cyclization. Failure to model cyclization can lead to erroneous conclusions.;The effects of organic substituents and solvent on polycondensation kinetics are examined by fitting a model with these features to 29Si NMR data. While organic substitution and the extents of hydrolysis and condensation of a silicon site affect the hydrolysis rate, these substituents do not affect hydrolysis equilibrium. Substitution at the reacting site also affects the magnitude but not the existence of a negative condensation substitution effect. Cyclization depends strongly on organic substitution.;The deterministickinetic model fit to NMR data provides direct information only about local structure development, not about the polymer size and shape distribution. To understand the structural implications of the kinetic trends found, this thesis presents kinetic Monte Carlo simulations of alkoxysilane polymerization. The simulations show that extensive cyclization plays a major role in predicting structural features such as the gelation point. Cyclization also causes the polymer structure to depend on monomer concentration---a feature absent from previous models.;These simulations allow better agreement with experiment and will be useful in process design. For instance in coating operations, the simulations indicate that structure gradients appear and may cause excess shrinkage and stress at the free surface---problems which may be addressed with design calculations.;Finally, this thesis extends quantitative kinetic modeling to copolymerization of pairs of alkoxysilanes. More kinetic parameters must be determined for these systems. To do so, the extent of copolymerization is determined indirectly by the dependence on composition of reaction rates in a semibatch reactor. These copolymerization models allow optimization of copolymer homogeneity and molecular structure by reactor design.