Chemistry Reference
In-Depth Information
The characteristic hydrogenated phenanthrene structure of rosin acids is similar
in rigidity to that of those petroleum-based aromatic or cycloaliphatic compounds
mentioned above. Therefore, through reactions of the carboxyl group and carbon-
carbon double bond in the molecules of rosin acids, the resulting rosin derivatives may
serve as substitutes for the petroleum-based cyclic (aliphatic and aromatic) monomers
used in epoxy and curing agent syntheses. In this chapter, the preparation of various
dicarboxylic acids and anhydrides derived from rosin acids and the application of
these anhydrides in epoxy curing are discussed in detail.
Figure 1.1
Some aromatic and cycloaliphatic anhydride curing agents.
1.2 Curing of Anhydride Type Derivatives of Rosin Acid with Epoxy
There is a free carboxylic acid group in each rosin acid molecule which can react
with epoxide to form an ester linkage. However, in order to crosslink an epoxy
resin, the curing agent needs to have at least two curable groups in one molecule.
The conjugated double bond of levopimaric acid is susceptible to the Diels-Alder
addition reaction, therefore a carboxylic acid or a carboxylic anhydride group can be
conveniently introduced by reacting levopimaric acid with dienephiles such as acrylic
acid or maleic anhydride. Since other isomeric rosin acids can undergo isomerisation
at elevated temperatures and assume the form of levopimaric acid which can be
subjected to Diels-Alder addition, the mixture of rosin acids can be used directly in
the synthesis of diacids or anhydrides.
Figure 1.2
illustrates the isomerisation of rosin
