Effect of Annealing on the Rheological and Thermal Properties of Aliphatic Hyperbranched Polyester Based on 2,2-Bis(methylol)propionic Acid

Abstract

We investigated the effects of annealing on the rearrangement of H-bonding structure and its influence on the thermal and rheological properties of a fourth-generation hyperbranched polyester polyol based on 2,2-bis(methylol)propionic acid (Boltorn H40). With increasing annealing time and decreasing temperature, the enthalpy of the endothermic transition in the DSC thermograms of Boltorn H40 increases, whereas the viscoelastic response shows a considerable elastic contribution. During annealing of amorphous Boltorn H40, its structure becomes more ordered as a consequence of formation of multiple intermolecular H-bonds (−OH...OC〈 and/or −OH...−OH) between long linear sequences in the hyperbranched structure. DSC, FTIR, and XRD results of the individual fractions of Boltorn H40 and an ideally structured dendrimer analogue show that the ordering of the structure is highest in the case of low molar mass hyperbranched species with an open structure and low degree of branching. Such species have the longest average length of linear sequences between branch points and therefore the highest possibility for multiple H-bond interactions.