Use of Rosin Acids as Rigid Building Blocks in the Synthesis of Curing Agents for Epoxies - Rosin-based Chemicals and Polymers - page 3

acids and conversion to anhydride or diacid via the Diels-Alder reaction. This synthesis
of rosin-derived anhydrides or diacids is very similar to the preparation of current
cycloaliphatic anhydride type curing agents which are all based on the addition of
various dienes with maleic anhydride, such as the addition of cyclo-1,3-pentyl diene
and maleic anhydride for nadic anhydride. There is a good structural resemblance
between rosin-derived anhydrides and petroleum-based cycloaliphatic anhydrides,
except that the former are more bulky and tend to have high melting points.
Figure 1.2 Rosin-derived diacids and acid anhydrides.
The curing kinetics of a rosin-derived anhydride curing agent and epoxy were simulated
by monitoring the reaction of methyl maleopimarate (MMP) and phenyl glycidyl
ether under nonisothermal differential scanning calorimetry (DSC) experimental
conditions [1]. Figure 1.3 shows the exothermic heat flow, degree of conversion and
reaction rate of nonisothermal curing of the model compounds under different heating
rates. The DSC results are summarised in Table 1.1 In Figure 1.3a , the initial curing
temperature ( T i ), peak exothermic temperature ( T p ) and temperature at the end of
cure ( T e ) all shifted to higher temperatures as the heating rate (β) increased, and the
range of curing temperature widened. However, the curing time actually decreased
with increase in heating rate because curing took place at higher temperatures. The
shift in cure temperature with heating rate is probably a methodological phenomenon.