ABSTRACT:The preparation and characterization of a class of alkoxy-modified silsesquioxane (AMS) compounds containing less than 5 wt % of latent alcohol is described. The AMS derived from octyl triethoxysilane (OTES) behaves as a shielding agent in silica-filled rubbers while significantly reducing the volatile organic compounds that are released during the manufacture of rubber articles. Analysis of AMS by high pressure liquid chromatography and 29 Si NMR shows that it has a plethora of structures present that can best be described as a highly condensed opened oligomeric, branched arrangement of silsesquioxanes units. This structure is moisture stable, hydrocarbon soluble, and reactive with silica at compounding temperatures. The AMS has been prepared by acid-or base-catalyzed hydrolysis and condensation in alcohol solution to form a product that often separates from the lower density reaction mixture. The kinetics of the AMS formation was examined and showed two separate rate processes occurring. The co-AMS prepared from OTES and 3-mercaptopropyl trimethoxysilane yielded an effective shielding agent and coupling agent when used in silica-filled vulcanizates.
Bulk viscoelasticity and tensile behavior are examined for cross-linked compounds made of mussel-mimetic elastomers of varied functionality design. During polymerization, the mussel-mimetic functionalities containing the 3,4-dihydroxyphenyl (or catechol) group can be incorporated at the molecule chain head, along the backbone, and/or at the molecule chain tail. The compounds are either unfilled or filled to the same filler volume fraction with a single filler chosen among carbon black (hydrophobic), precipitated silica (hydrophilic), and titanium oxide (hydrophilic). For polymers bearing multiple mussel-mimetic functional groups, the polymer cold flow resistance becomes significantly enhanced, arising from the strong intermolecular hydrogen bonding interactions. Such strong intermolecular hydrogen-bonding interactions also affect the bulk viscoelasticity and tensile behavior for the cross-linked gum compounds. Because the mussel-mimetic functional groups exhibit obvious affinity to all three types of filler particles, the extent of modification to bulk viscoelasticity and reinforcement for the filled compounds is observed to vary with the distribution of such functionalities along a polymer molecule, the chemical groups immediately next to the catechol group, and the specific type of filler. As expected, microscale filler dispersion is improved from the strong polymer–filler interactions.
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