Hyper-branched polymers (HBPs) based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) have recently been studied due to their commercial availability, chemical stability, and their wide variety of industrial applications. Although they are widely available, the relationship between their structure and bulk physical properties have yet to be fully explored. More specifically, due to the high concentration of hydroxyl groups available, bis-MPA based HBPs can form extensive intra and inter molecular hydrogen bonds (H-bonds) which play an important role in defining their bulk properties. The physical properties of bis-MPA based HBPs are highly influenced by the presence of water, likely due to an increase in available H-bond doners and acceptors provided by water molecules. Because of this, humidity is an important environmental contributor to the overall bulk properties of the systems. To explore this effect, an investigation on the water uptake kinetics of this material was performed in order to understand the quantity of uptake, its effects on bulk properties, and how to optimize effects for best practices. To start this investigation, thermogravimetric analysis (TGA) was employed to provide insight on how much water is present in samples over a broad humidity range and Fourier transform infrared spectroscopy (FTIR) allowed for a comprehensive look at H-bond formation throughout the samples. Additionally, wide angle x-ray scattering (WAXS) was used to compare the structural order differences between different generations of bis-MPA based HBPs. It was found that the uptake kinetics of water was proportional to the relative humidity that the sample was exposed to, where samples exposed to a higher humidity absorb a higher quantity of water at a faster rate than samples exposed to a lower relative humidity. The HBP samples also displayed much more hydrophilic characteristics than linear samples with the same functional groups.

Investigating the effect of humidity on the hydrogen bond organization of hyperbranched polymers

ACS Spring 2022

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