Cationic polymers are of broad interest in the biotechnology sector due to their potential use in drug conjugation, tissue engineering, gene delivery, water purification and chelation, and stimuli-responsive materials. Of particular interest in designing cationic polymers is control over their pKa—allowing for the presentation of a positive charge at specific pH, which is dependent on molecular weight, connectivity, and pendant group identity of the polymer. Most cationic polymers incorporate amine groups to produce this positive charge; for example, poly(ethylene imine), a commercially available polymer with a pKa of 7-8.6, will display a positive charge at or below physiological pH. Polymers of similar pKa can exhibit this same positive charge; however, at pH very close to the pKa, only a fraction of the polymer’s groups will be protonated according to the Henderson-Hasselbalch equation. Because of this reason, cationic polymers with amine groups can display a wide range of variation in their interactions with biological molecules. To address this issue, we designed and synthesized a series of monomers and polymers that should be constitutively protonated at or around physiological pH; these polymers are based on pyrrolidine and piperidine (pKa~11.2-11.3). Using free radical polymerization, the series of polymers were synthesized—varying charge density via copolymerization with vinyl pyridine (pKa~5.2) and neutral monomer hydroxyethylmethacrylate. Subsequent complexation of these polymers and copolymers with biological molecules was investigated by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS)—showing notable differences in complex formation. Systematic manipulation of monomer identity and characteristics help to shape our understanding of the variation in resultant complex geometry.

Cationic polymers incorporating pyrrolidine and piperidine

ACS Spring Meeting 2021

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