A Comparative Study of Hydrogen Bond Organization between Hyperbranched Polymers and Dendrimers Based on bis-MPA

Physical properties hyperbranched polymers (HBPs) based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA), which have been widely studied, are largely determined by the hydrogen bonds (H-bonds). However, similar studies have not yet been extended to bis-MPA based dendrimers which require considerable synthetic efforts. In this study, hydrogen bond organization and interrelated structural order formation of a bis-MPA based second-generation dendrimer (D2) were investigated in comparison with its HBP analogue (HBP2). WAXS spectra of both polymers showed similar structural ordering originated from clustering of multiple hydroxyl groups mediated via H-bonds. MD simulations well predicted the WAXS spectra and revealed ‘chain-like’ clusters of different lengths from single H-bond associations to clusters containing tens of hydroxyls. D2 showed higher propensity of forming long clusters than HBP2 indicating terminal hydroxyls are more capable of forming long associations than linear ones. Meanwhile, an additional narrow peak which superimposed on the amorphous halo was only observed on the WAXS spectra of HBP2. The origin of this narrow peak was assigned to a pseudo-hexagonal mesophase formed by linear chain segments.