Page 422 - Handbook of Adhesives and Sealants

Adhesives Families 365

Epoxy Ring - Opening Polymerization
O O
/ \ / \
- -
B + R − CH − CH 2 → B − CH 2 − CH − O + R − CH − CH 2 → B [− CH 2 − CH − O −] n
 
R R
Anion Epoxy

H

+
O O O
/ \ / \ / \
+
H + R − CH − CH 2 → B − CH − CH 2 + R − CH − CH 2 → HO [− CH − CH 2 − O −] n

R
Cati Epoxy
Figure 10.3 (Continued)

amines are primarily used as catalysts but can be used as a room
temperature or elevated temperature curing agent on their own. Ar-
omatic amines are generally solid curing agents and can be used to
provide a B-staged cure with most epoxy resins. Typical aromatic
amines include m-phenylenediamine (MDA) and diaminodiphenyl sul-
fone (DDS).
The amido-amine curatives are polyamides with amine functionality
and lower viscosity. They cure relatively quickly at room temperature,
and they develop tougher bonds than do the amine or mercaptan cured
systems. Their properties are very similar to the polyamide cured ep-
oxy systems. The amido-amines are generally less corrosive to skin
than standard amine curatives. These curing agents are used in the
standard two component epoxy adhesive that have a one-to-one mixing
ratio (resin and hardener by weight), and they will gel in about 30–
60 mins with 12–24 hrs required for full cure. Such systems can read-
ily be found commercially in viscosities ranging from motor oil to clay-
like.
The epoxy/mercaptan reaction is normally catalyzed with a tertiary
amine and is used for the standard two component, five minute curing
epoxies that can be found in hardware stores. These fast curing prod-
ucts have a tendency to be somewhat brittle and may perform quite
poorly in the peel mode. Mercaptan cured epoxy adhesives have a
strong sulfur-like odor that can be an irritant.
Anhydride cured epoxy systems exhibit low viscosity, long pot life,
and low exotherm. The epoxy/anhydride reaction normally must use
heat to complete the cure. Anhydride cures can be accelerated with
tertiary amines such as tris (dimethylaminomethyl) phenol (DMP30).
They form good high temperature resistant products, but have a ten-