Degree Name
Master of Science (MS)
Semester of Degree Completion
1998
Thesis Director
Jonathan P. Blitz
Abstract
Pretreated silica gels with distinct silica surfaces containing either isolated silanols, vicinal silanols, siloxanes, or some combinations of the three, were reacted with several organometallic compounds to determine how each compound reacted with the different silica surface species. The organometallic compounds used were trimethylaluminum, triethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, methylaluminoxane, dibutylmagnesium, and bis-cyclopentadienyl dimethyl zirconium.
These reacted silica gels were analyzed using diffuse reflectance infrared Fourier transform spectroscopy and ICP-AES elemental analysis. CH/Metal ratios were calculated using specific peaks in the IR spectra to elucidate the surface bonded species. Elemental analysis was used to determine how much metal was bonded to each silica gel surface.
Elemental analysis showed that under the conditions studied all of the compounds had reactivities with respect to the four silica gel surfaces following the order of bare silica > 600°C silica > HMDS silica > 600°C/HMDS silica. All of the compounds, with the exception of dimethylzirconocene (which only reacts appreciably with isolated silanols), react with both isolated and vicinal silanols, and appear to react significantly with the siloxane groups.
Based on CH/Metal ratios, all compounds are believed to react with isolated silanols forming singly bonded surface structures. Most of the compounds also appear to form bridged surface species after reaction with vicinal silanols. EADC, however, is believed to react with each silanol in a hydrogen bonded silanol pair, yielding two dichloroaluminum surface groups. Most of the compounds also seem to react appreciably with siloxanes, resulting in siloxane bond cleavage. The theoretical CH/Metal ratios for each compound were calculated to follow the order of 600°C/HMDS silica > 600°C silica > bare silica > HMDS silica. There were some differences between the theoretical and experimental ratio orders but, in most cases they were comparable.
Recommended Citation
Diebel, Richard E. III, "Reactions of Modified Silica Gel Surfaces with Organometallic Compounds: Enhancing Olefin Polymerization Catalysts" (1998). Masters Theses. 1740.
https://thekeep.eiu.edu/theses/1740
