Heterogeneous hydrogenation of model polystyrenes and functionalized derivatives

Heterogeneous hydrogenation of model polymers is an effective method for the preparation of model polyolefins. Due to their fully saturated nature, polyolefins have many desirable properties, including increased resistance to thermal, oxidative, and radiation-induced degradation. However, heterogeneous polymer hydrogenation is a complex process influenced by many variables. The goals of the research presented in this dissertation are two-fold; to gain a better fundamental understanding of the process of heterogeneous polymer hydrogenation, and to utilize this valuable technique for the synthesis of novel materials based on hydrogenated polymers.; A kinetic study of the heterogeneous catalytic hydrogenation of model polystyrenes (PS) using a catalyst comprised of Pt on a wide-pore silica support was performed. The effect of molecular weight on the initial rate of hydrogenation, r_o, was investigated under conditions where mass transfer limitations were minimized. The r_o values for a series of model polystyrenes ranging in molecular weight from ca. 1.0 to 300 kg/mol were measured. For molecular weights up to 102 kg/mol, r_o scaled with the number-average degree of polymerization, X_n, to the −0.15 power. The results were explained in terms of equilibrium structure and conformational dynamics of a polymer on a metal surface, interchain interactions, and the relative dimensions of the polymer coils and Pt crystallites. All hydrogenated products were analyzed by size exclusion chromatography (SEC), 1H NMR spectroscopy and ultra-violet (UV) spectroscopy.; The synthesis and characterization of model, low-molecular-weight, α,ω-dihydroxy poly(cyclohexylethylene), HO-PCHE-OH, was accomplished. Anionic polymerization of styrene using the protected hydroxyl-functionalized organolithium initiator, t-butyldimethylsiloxypropyllithium (PFI-3), (in predominantly non-polar media) at 10°C, followed by ethylene oxide termination resulted in α- t-butyldimethylsiloxy,ω-hydroxy polystyrene, TBDMSO-PS-OH. Hydrogenation of TBDMSO-PS-OH using a Pd/CaCO₃ catalyst, at 120°C and 500 psig H₂ for 24 hours, followed by quantitative removal of t-butyldimethylsilyl (TBDMS) protecting group afforded HO-PCHE-OH. Both α,ω-dihydroxy PS and α,ω-dihydroxy PCHE were utilized as the polyol in polycondensation reactions with 4,4 ′-methylenebis(phenyl isocyanate) and the chain extender 1,4-butanediol, to form segmented polyurethane block copolymers. All materials were characterized via SEC, 1H and 13C NMR spectroscopy, infrared (IR) spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry.