In this way, two chains have been linked, and the reaction
will proceed further from the remaining acetoxy groups.
An organometallic tin catalyst is normally used. The crosslinking
reaction requires moisture to diffuse into the material.
Accordingly cure will proceed from the outside surface inward.
These materials are called one-part RTV (room temperature
vulcanization) sealants, but actually require moisture as a second
component. Acetic acid is released as a by-product of
the reaction. Problems resulting from the acid can be overcome
using other cure (cross-linking) systems that have been
developed by replacing the acetoxysilane RSi(OAc)3 with
oximosilane RSi(ON=CR′
2)3 or alkoxysilane RSi(OR′)3.
Condensation curing is also used in some two-part systems
where cross-linking starts upon mixing the two components,
e.g., a hydroxy end-blocked polymer and an alkoxysilane such
as tetra-n-propoxysilane (Noll, 1968):
In this way, two chains have been linked, and the reaction
will proceed further from the remaining acetoxy groups.
An organometallic tin catalyst is normally used. The crosslinking
reaction requires moisture to diffuse into the material.
Accordingly cure will proceed from the outside surface inward.
These materials are called one-part RTV (room temperature
vulcanization) sealants, but actually require moisture as a second
component. Acetic acid is released as a by-product of
the reaction. Problems resulting from the acid can be overcome
using other cure (cross-linking) systems that have been
developed by replacing the acetoxysilane RSi(OAc)3 with
oximosilane RSi(ON=CR′
2)3 or alkoxysilane RSi(OR′)3.
Condensation curing is also used in some two-part systems
where cross-linking starts upon mixing the two components,
e.g., a hydroxy end-blocked polymer and an alkoxysilane such
as tetra-n-propoxysilane (Noll, 1968):
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