Synthesis and characterization of bis-MPA-based polymers
Polymers are used in everyday life. From natural polymers, like cellulose, silk, deoxyribonucleic acid (DNA), and proteins, to commonly known synthetic polymers, such as nylon, polyester, and Teflon. Polymers have also been used in biomedical applications for drug delivery and as diagnostic imaging agents. These are only a few of the many uses for polymers. The most commonly used and studied polymers are linear, but in the past 40 years, branched polymers have become a point of interest. These branched polymers range from perfectly branched dendrimers to randomly branched polymer, which contain varying degrees of branching. Different architectures have proven to yield substantial changes in physical properties (i.e., mass, size, thermal stability, etc.). By altering the architecture of a polymer, along with changes in chemical composition, a finely tuned material with the optimized properties is attainable. One complication with hyperbranched polymers is the accurate and precise characterization of these materials. The random branching can make conventional analytical methods obsolete, so new techniques of analysis need to be tested. In this work, multiple analytical techniques are used to compare hyperbranched polymers to dendrimers and linear polymers. This comparison is rare due to the lack of monomers that can be used for both linear and branched polymers but is necessary for the enhanced understanding that comes from a more accurate characterization method. In this work, conventional gel permeation chromatography (GPC) and multiangle light scattering (MALS) are used to determine the molecular weight and hydrodynamic radii of the polymers. By both methods, the hyperbranched polymer appeared smaller than the linear polymer, but larger than the dendrimer. A similar trend is observed in the thermal analysis, where the dendrimer showed more thermal stability than the linear polymer. The hyperbranched polymer showed multiple thermal degradation events, a higher temperature that correlates to dendritic features and a slightly lower temperature that corresponds with linear character. Additional data obtain via tandem mass spectrometry (MS2) demonstrates further similarities between the hyperbranched polymer and the linear polymer by the presence of fragment ions related to the backbiting, which is not favored for the dendritic structure. There are also similarities between the hyperbranched polymer and the dendrimer, which are seen by the formation of the methyl acrylate fragment that is not available in the linear polymer. These multiple analytical techniques commonly display that the hyperbranched polymers indeed contain dendritic and linear components, which can both contribute to the expression of properties. In this work, 2,2’-bis(hydroxymethyl)propionic acid (bis-MPA), or an AB2-type monomer is used. Bis-MPA is a versatile, cost efficient, non-toxic monomer. It can be used for the synthesis of linear polymers, hyperbranched polymers, and dendrimers on multi-gram scales. The hydroxy end groups can be functionalized with many different end groups; benzoyl esters and benzylidene protecting groups are used in the work herein. By understanding bis-MPA-based polymers, its potential as a highly commercialized material can be achieved. This work lays the groundwork for further investigation, specifically for branched materials.