Caffeic
acid was esterified and then successfully converted with
ethylene carbonate into a new potentially fully bio-based aromatic
diol containing a pendant α,β-unsaturated ester. The lipase
B from Candida antarctica allowed the
synthesis of polyesters from this caffeic-based diol and diethyl adipate.
1,6-Hexanediol was also used as a second diol monomer to study the
impact of the aromatic diol proportion on the enzymatic activity and
final material properties. For caffeic diol (CD) ratios of 10% and
above, linear polyesters were obtained with M
w up to 28 000 g·mol–1. Increasing
the ratio of CD tended to reduce the polyester final molar masses,
probably due to inhibition of the enzyme. However, increasing the
proportion of CD in the polyester improved its thermal properties,
with T
g reaching up to 12 °C. Finally,
the pendant double bonds of the polyester were shown to undergo [2
+ 2] cycloaddition under light irradiation, enabling its UVA-activated
cross-linking. This cross-linking was also shown to be partially reversible,
thanks to the UVC-induced splitting of the cyclobutane rings in the
network.