Introducing free carboxylic acid groups along polyester chains using dimethylolpropionic acid as diol component

While different biodegradable polyesters have already been developed as green alternatives in food packaging, replacing functional polymers as present for example in superabsorbers is more complex due to the lack of selectivity in industrial polyester production. In this work, the trifunctional dimethylolpropionic acid (DMPA) was shown to react selectively as a diol component choosing the right reaction partners, introducing free carboxylic acid groups along the polyester chain. The reaction behavior was thoroughly investigated using a multimethod approach including NMR spectroscopy, MALDI mass spectrometry, and HPLC-MS. While reaction with adipic acid and 1,4-cyclohexanedicarboxylic acid was successful, material properties were inferior due to glass transition temperatures of the resulting polymers below 20 °C. A significant increase of Tg values up to 50 °C was obtained by introducing the aromatic isophthalic acid which could however not be realized in a direct reaction. Instead, a precondensate of isophthalic acid and neopentyl glycol was synthesized followed by the simultaneous addition of DMPA and the (cyclo)aliphatic acids. This protocol and the detailed description of characterization methods allow further investigations of DMPA polyester systems which carry potential in the fields of drug delivery, hydrogels, and superabsorbers as well as coatings, dispersants, and waste water treatment.