Chemistry Reference
In-Depth Information
can be accomplished by reactions with peroxides through abstractions of tertiary hydrogens with free
radicals:
O
O
O
O
C
2
H
5
C
2
H
5
+
R
+
RH
O
O
C
2
H
5
O
O
2
C
2
H
5
C
2
H
5
O
O
Another way to cross-link acrylic elastomers is through a Claisen condensation:
O
O
C
2
H
5
O
O
C
2
H
5
base
+
O
O
C
2
H
5
O
The above illustrated cross-linking reactions of homopolymers, however, form elastomers with
poor aging properties. Commercial acrylic rubbers are, therefore, copolymers of ethyl or butyl
acrylate with small quantities of comonomers that carry special functional groups for cross-linking.
Such comonomers are 2-chloroethylvinyl ether or vinyl chloroacetate, used in small quantities (about
5%). These copolymers cross-link through reactions with polyamines.
6.14.3 Thermoplastic and Thermoset Acrylic Resins
Among methacrylic ester polymers, poly(methyl methacrylate) is the most important one industrially.
Most of it is prepared by free-radical polymerizations of the monomer and a great deal of these
polymerizations are carried out in bulk. Typical methods of preparation of clear sheets and rods
consist of initial partial polymerizations in reaction kettles at about 90
C with peroxide initiators.
This is done by heating and stirring for about 10 min to form syrups. The products are cooled to room
