Chemistry Reference
In-Depth Information
H
H
C = CH
2
C = CH
2
COOH
COOH
COOH
COOH
COOH
Abietic acid
Levopimaric acid
Dehydroabietic acid
Pimaric acid
Isopimaric acid
Figure 4.1
Representative structures of resin acids
The resin acids can isomerise under heat and/or acidic conditions and give an
equilibrium mixture of resin acids [66]. Carboxyl and double bonds are the important
functional groups and are the focus for chemical modification.
4.3 Gum Rosin-derived Polymers
A great deal of effort has been devoted to the preparation of renewable polymers
by condensation polymerisation. There are only a few reports on the free radical
polymerisation of rosin-derived vinyl monomers [39-42, 44, 45, 67, 68]. According
to the position of the hydrophenanthrene ring in the polymer structures, gum rosin-
based polymers are classified into main chain and side chain polymers.
4.3.1 Main Chain Rosin-based Polymers
The synthesis of main chain rosin-based polymers is usually carried out through step-
growth polymerisation. Resin acids and their derivatives are expected to improve
rigidity and chemical/heat resistance and can be suitable substitutes of petroleum-based
compounds such as trimellitic anhydride, benzophenonetetracarboxylic dianhydride
and pyromellitic dianhydride.
Resin acids react with MA to form a Diels-Alder adduct, which contains one carboxyl
group and one anhydride group capable of condensation polymerisation. However,
most of these polymers have low molecular weight (typically oligomers) probably
due to the steric hindrance of the hydrogenated phenanthrene ring, and the sensitivity
to impurities and variations in stoichiometry in step-growth polymerisation. Some
of resin acid-derived monomers (
1
-
8
) are shown in
Figure 4.2
. The rosin-based
monomers are difunctional or trifunctional compounds and can be used to synthesise
multifunctional polyesters, polyamides, polyesterimides, polyester polyols, and so on.
