Preparation and Characterisation of Epoxy Binders Based on Rosin - Rosin-based Chemicals and Polymers - page 46

also used for curing powder coatings. In this reaction, which requires both initiation
and catalysis, polyesters are produced both rapidly and exothermically without any
water of reaction being evolved because hydroxyl groups will always be present when
epoxy resins are being cured, even when other reactive groups predominate. It should
be noted that conditions of temperature and catalysis may enhance or suppress the
possible etherification reaction with hydroxyl in relation to the other epoxy group
reactions .
Polyamides are extremely versatile curing agents. They are inexpensive and can be
mixed with epoxy resins at any ratio. Methods of preparing polyamides based on
rosin acid are described in the rest of this section. In the large majority of cases,
polyamides are derived from MA or pyromellitic anhydride. Atta and co-workers [36,
37] prepared series of poly(amide-imide)s based on Diels-Alder adducts of rosin acid
and its ketone with both MA and AA. The reaction between rosin acid and DAK with
both AA and MA produces monomers which have dicarboxylic end groups in their
structures. These groups can participate in polycondensation reactions with TETA
and PEHA. The reaction scheme for the condensation of APA and MPA with both
TETA and PEHA is represented in Scheme 2.7 , while the scheme for the condensation
of both AA/DAK and MA/DAK with TETA and PEHA is illustrated in Scheme 2.8 .
The products of polycondensation of APA, MPA, AA/DAK and MA/DAK with TETA
were designated here as APATA, MPATA, AA/DAKTA and MA/DAKTA, respectively.
While the designations of these products with PEHA, were APAPA, MPAPA, AA/
DAKPA and MA/DAKPA, respectively. The purity of the produced polymers was
determined from elemental analysis and acid numbers as listed in Table 2.7 . The
structures and purity were confirmed by IR and 1 H-NMR spectroscopy [37].
Scheme 2.7 Condensation of APA and MPA with both TETA and PEHA