Dendrimers are known for their perfectly branched, monodisperse, symmetric structure. Their hyperfunctional periphery has led to numerous applications for drug delivery, magnetic resonance imaging, and as diagnostic agents. The purpose of this investigation is to study the reactivity and accessibility of functional groups in bis(hydroxymethyl)propanoic acid (bis-MPA) dendritic and hyperbranched polymers. Reaction rates associated with the esterification of dendritic polymers are compared to those displayed by hyperbranched polymers. Architecture and end group availability play a substantial role in reactivity, which should lead to a more fundamental understanding of local and global steric interactions. Preliminary results demonstrate the significant impact of sterics on the rate of reactivity. Investigating the synthesis of a second-generation tetra-core dendrimer from the deprotected first generation precursor, there are eight hydroxyls available to be functionalized. These end groups are a direct result of the previous esterification and deprotection, so the end groups are available in four pairs. In the subsequent esterification, it seems more likely that one hydroxyl from each of the four pairs will react before the second hydroxyl from any other pair reacts. The first four dendritic substituents add in the first few minutes, while the last four dendritic substituents can take up to several hours. As the reaction progresses, the availability of the end groups decreases substantially, which slows the reaction rate. Similarly, hyperbranched polymers show a drastic decrease in reactivity as the reaction progresses. Although the two systems display varying reaction rates at the same molecular weight, both show similar trends of slowing reactivity rates. This relationship can be used to influence the degree of branching based on reaction time, especially when doing post-polymerization modifications. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS) and proton nuclear magnetic resonance (<sup>1</sup>H NMR) have been used to determine the progress of the reaction at a given time. Specifically, preparative gel permeation chromatography (prep-GPC) was used to isolate polymers by degree of functionality for <sup>1</sup>H NMR analysis. The combination of these analytical techniques will lend to a better understanding of the reactivity of complex polymeric systems to tune properties based on branching.

Kinetic analysis of the reactivity in bis-(hydroxylmethyl)propionic acid-based dendritic and hyperbranched polymer systems

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.