Cyanoacrylates
are a family of strong fast-acting
adhesives
with
industrial, medical, and household uses. They are derived from
ethyl
cyanoacrylate
and related
esters
. The cyanoacrylate group in the
monomer rapidly
polymerizes
in the presence of water to form long,
strong chains.
The most common monomer is
ethyl cyanoacrylate
. Several related
esters are known. To facilitate easy handling, a cyanoacrylate
monomer is frequently formulated with an ingredient such as
fumed
silica
to make it more
viscous
or gel-like
In general, the C=C groups rapidly undergo
chain-growth
polymerisation
in the presence of water (specifically
hydroxide ions
),
forming long, strong chains, joining the bonded surfaces together.
Because the presence of moisture causes the glue to set, exposure to
normal levels of
humidity
in the air causes a thin skin to start to form
within seconds, which very greatly slows the reaction; hence,
cyanoacrylates are applied as thin coats to ensure that the reaction
proceeds rapidly for bonding. Cyanoacrylate adhesives have a
short
shelf life
-about one year from manufacture if unopened, and one
month once opened