Biobased functional polyesters for coating applications: Synthesis, characterization and application

Thermosetting coating systems contain polyesters as binders. A crucial property of these polymers is their functionality. During coating application, the polyesters are cross-linked in situ, which means that each polymer chain needs a sufficient no. of reactive end-groups. Renewable monomers are attractive starting materials for polyester synthesis, since building blocks with great functional diversity are available from many resources. Aliph. polyesters were synthesized through polycondensation of renewable monomers such as isosorbide, isoidide and 2,3-butanediol in combination with succinic or adipic acid. Glycerol was added to the polymn. mixt. to enhance the polyester hydroxyl functionality. Reacting OH-functional resins with citric acid yielded polyesters with carboxylic acid end-groups and significantly increased functionality. Glassy polyesters with Mn > 2000 g/mol and Tg > 45 DegC were synthesized, having either hydroxyl or carboxylic acid end-groups. Chem., functionality and structure-property relations of these polyesters will be discussed, as well as their applicability in thermosetting coatings