Chemistry Reference
In-Depth Information
Table 6.12
Typical components of thermoset acrylic resins
Monomers that contribute rigidity
Flexibilizing monomers
Monomers used for cross-linking
Methyl methacrylate
Ethyl acrylate
Acrylic acid
Ethyl methacrylate
Isopropyl acrylate
Methacrylic acid
Styrene
Butyl acrylate
Hydroxyethyl acrylate
Vinyl toluene
i
-Octyl acrylate
Hydroxypropyl acrylate
Acrylonitrile
Decyl acrylate
Glycidyl acrylate
Methacrylonitrile
Lauryl methacrylate
Glycidyl methacrylate
Acrylamide
Aminoethyl acrylate
temperature and various additives may be added. The syrups are solutions of about 20% polymer
dissolved in the monomer. They are poured into casting cells where the polymerizations are
completed. The final polymers are high in molecular weight, about 1,000,000.
Poly(methyl methacrylate) intended for surface coatings is prepared by solution polymerization.
The molecular weights of the polymers are about 90,000 and the reaction products that are 40-60%
solutions are often used directly in coatings.
A certain amount of poly(methyl methacrylate) is also prepared by suspension polymerization.
The molecular weights of these polymers are about 60,000 and they are used in injection molding and
extrusion.
Thermosetting acrylic resins are used widely in surface coatings. Both acrylic and methacrylic
esters are utilized and the term is applied to both of them. Often such resins are terpolymers or even
tetra polymers where each monomer is chosen for a special function [
214
]. One is selected for
rigidity, surface hardness, and scratch resistance; another for the ability to flexibilize the film, and the
third one for cross-linking it. In addition, not all comonomers are necessarily acrylic or methacrylic
esters or acids. For instance, among the monomers that may be chosen for rigidity may be methyl
methacrylate. On the other hand, it may be styrene instead, or vinyl toluene, etc. The same is true of
the other components. Table
6.12
illustrates some common components that can be found in
thermoset acrylic resins.
The choice of the cross-linking reaction may depend upon desired application. It may also simply
depend upon price, or a particular company that manufactures the resin, or simply to overcome patent
restrictions. Some common cross-linking reactions will be illustrated in the remaining portion of this
section. If the functional groups are carboxylic acids in the copolymer or terpolymer, cross-linking
can be accomplished by adding a diepoxide.
O
O
+
+
COOH
COOH
R
OO
OO
OH
OH
