TY - JOUR
T1 - Enhancing the functionality of biobased polyester coating resins through modification with citric acid
AU - Noordover, Bart A.J.
AU - Duchateau, Robbert
AU - van Benthem, Rolf A.T.M.
AU - Ming, Weihua
AU - Koning, Cor E.
PY - 2007/12
Y1 - 2007/12
N2 - Citric acid (CA) was evaluated as a functionality-enhancing monomer in biobased polyesters suitable for coating applications. Model reactions of CA with several primary and secondary alcohols and diols, including the 1,4:3,6-dianhydrohexitols, revealed that titanium(IV) n-butoxide catalyzed esterification reactions involving these compounds proceed at relatively low temperatures, often via anhydride intermediates. Interestingly, the facile anhydride formation from CA at temperatures around CA's melting temperature (Tm = 153 °C) proved to be crucial in modifying sterically hindered secondary hydroxyl end groups. OH-functional polyesters were reacted with CA in the melt between 150 and 165 °C, yielding slightly branched carboxylic acid functional materials with strongly enhanced functionality. The acid/ epoxy curing reaction of the acid-functional polymers was simulated with a monofunctional glycidyl ether. Finally, the CA-modified polyesters were applied as coatings, using conventional cross-linking agents. The formulations showed rapid curing, resulting in chemically and mechanically stable coatings. These results demonstrate that citric acid can be applied in a new way, making use of its anhydride formation to functionalize OH-functional polyesters, which is an important new step toward fully biobased coating systems.
AB - Citric acid (CA) was evaluated as a functionality-enhancing monomer in biobased polyesters suitable for coating applications. Model reactions of CA with several primary and secondary alcohols and diols, including the 1,4:3,6-dianhydrohexitols, revealed that titanium(IV) n-butoxide catalyzed esterification reactions involving these compounds proceed at relatively low temperatures, often via anhydride intermediates. Interestingly, the facile anhydride formation from CA at temperatures around CA's melting temperature (Tm = 153 °C) proved to be crucial in modifying sterically hindered secondary hydroxyl end groups. OH-functional polyesters were reacted with CA in the melt between 150 and 165 °C, yielding slightly branched carboxylic acid functional materials with strongly enhanced functionality. The acid/ epoxy curing reaction of the acid-functional polymers was simulated with a monofunctional glycidyl ether. Finally, the CA-modified polyesters were applied as coatings, using conventional cross-linking agents. The formulations showed rapid curing, resulting in chemically and mechanically stable coatings. These results demonstrate that citric acid can be applied in a new way, making use of its anhydride formation to functionalize OH-functional polyesters, which is an important new step toward fully biobased coating systems.
UR - http://www.scopus.com/inward/record.url?scp=38049080558&partnerID=8YFLogxK
U2 - 10.1021/bm700775e
DO - 10.1021/bm700775e
M3 - Article
C2 - 17994697
AN - SCOPUS:38049080558
SN - 1525-7797
VL - 8
SP - 3860
EP - 3870
JO - Biomacromolecules
JF - Biomacromolecules
IS - 12
ER -