Hyperbranched polyesters and their application in dental composites: monomers for low shrinking composites

Using trimethylolpropane (TMP) and 2,2‐bishydroxymethylpropionic acid (Bis‐MPA), aliphatic hyperbranched polyesters (HBP) were synthesized, with a degree of branching of DB = 0.47 and a degree of polymerization of Pn = 16.5. Aromatic HBPs with repetitive units of 2,2‐bis(4‐hydroxyphenyl)pivalonic acid (Bis‐PVA) lead to a higher DB = 0.48 and Pn = 30.5 compared to the aliphatic HBP. Reactive functionalization of the hyperbranched polymers was achieved via esterification of mixtures of methacrylic acid and carboxylic acids. In this manner, i‐butyric acid and methacryloyl terminated HBPs were obtained. They have a low viscosity ranging from 200 to 364 Pa*s and exhibit relatively low volume shrinkage (1.9 to 3.6%) during photoinitiated cure. Dental composites with volume shrinkage of 0.5 to 1.5% have been prepared using these methacryloyl terminated HBPs in combination with a Ba/alumosilicate glass filler.