Electrostatic Interaction Regulation Of Aqueous RAFT Polymerization Of Ionic Monomers

Polypeptide chains, which are usually consisted of oppositely-charged polyelectrolytes,play a very important role in the formation of organs and tissues. How do chemistssynthesize well-defined polyelectrolyte? Through the interaction of regulation ofcontrolled radical polymerization is an effective way to realize the goal. The emerging"polymerization induced self assembly"(PISA) combines artificial synthesis with selfassembled. In recent years, chemists used amphiphilic block polymer gained from PISAhas revealed the relationship between acceleration of polymerization and self-assembly.As we all know, the production of polylelectrolytes in our body starts from smallmolecule and in-situ, but the study of self-assembly of polyelectrolytes have beenfocused on the supermolecular level, it’s important to study electrostatic interactionregulation of aqueous RAFT polymerization of ionic monomers. It will be helpful for usto comprehend how the electrostatic interaction to affect the copolymerization of ionicmonomers and provide methodological basis to synthesize polyelectrolytes of precisestructure for biological medical materials.Acceleration effect and selective radical addition during RAFT copolymerization ofthe oppositely-charged ionic monomers in dilute aqueous solution at25oC are discussedin this paper. A pair of anionic and cationic acrylamides,2-Acrylamido-2-methyl-propanesulfonic (AMPS), N-(2-Aminoethyl) acrylamide hydrochloride (AEAM), wasselected as model monomers. A kind of well-defined non-ionic water solublepoly(N-2-hydroxypropylmethacrylamide)(PHPMA) was synthesized via RAFTpolymerization in aqueous solution at ambient temperature, which was used as amacromolecular chain transfer agent (macro-CTA) and a steric stabilizer, and applysodium phenyl2,4,6-trimethylbenzoylphosphinate (SPTP) photoinitiator to copolymerizeionic monomers under identical conditions. The copolymerization of AEAM and AMPS in water and1.0M of sodium chlorideaqueous solution were studied, both the polymerization rate of AEAM and AMPS in1.0M sodium chloride aqueous solution are faster than these in pure water. The introductionof salt to polymerization increased electrostatic shielding and reduced electrostaticrepulsion between the monomers, so made faster polymerization rates, and prolonged theinitiation period. The reactivity activity of AMPS is higher than AEAM both in water andin1.0M NaCl solution. The aqueous GPC of AMPS extended with PHPMA wasinvestigated, indicated controllable polymerization.A fast iterative polymerization can be induced even in dilute solution by the favorableionic interactions and self-assembly of zwitterionic growing chains, which adds a newmechanism to the polymerization-induced self-assembly. Acceleration was amplified onvia addition of methanol but was suppressed in presence of added NaCl.Statistical copolymerization of ion-paired binary mixtures of co-monomers wereremarkably more efficient than the homo-polymerization of ionic monomers, leading to aequal apparent propagation rate constants (kapp) at1:1co-monomer feed ratios and aninvariably higher kappfor minor co-monomer when employing other feed ratios, whichprovides a new idea to sequence-controlled polymerization. Correlation between kineticsand self-assembly of zwitterionic growing chains has been investigated.These unique behaviors reveal the role of electrostatic interaction regulation inaqueous RAFT polymerization of ionic monomers, not only enrich the family ofpolymerization induced self-assembly, but also open an avenue toward rapid synthesis ofsequence-controlled zwitterionic polyelectrolyte that can satisfy demands of emergingbiological applications.