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Organosilicon Compounds General
Silicon is one of the few metals which form stable bonds with carbon, and this offers unique opportunities for producing molecules that can react with both filler surfaces and polymer matrices.
The filler-reactive side is based around to the silanol (Si-OH) functionality. This will readily react with filler surface hydroxyls to form strong bonds. Silanols will also self-condense, however, and so they cannot be present in the starting compound but must be generated in situ during the coating process. Thus, some silanol precursor must be used. While halogens can do this, the most common approach is to use an alkoxide group as the silanol precursor. Thus, most modifiers are based on silicon alkoxides.
Groups such as vinyl, amino, epoxy, mercapto, and sulphido can be stably attached to silicon using Si-C bonds, and these provide the reaction sites with the host polymer. Where no reactivity is required, then a simple group such as methyl suffices.
The organosilicon coupling agents in commercial use generally have three filler anchor groups (alkoxy) and only contain one organic group attached to silicon, the general formula being
They are often referred to simply as silanes.
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