Visible Light Activated Room-temperature Aqueous RAFT Polymerization Of Tertiary Amine Based Monomers Tuned By Ionic Association

The tertiary amine based polymers have attracted considerable attentions because of theirexceptionally remarkable properties for the applications in nano-and bio-related fields.Facileand rapid synthesis of well-defined polyelectrolytes under environmentally friendlyconditions is most important in polymer scientists. However, rapid and well-controlledaqueous polymerization of tertiary amine monomers under mild conditions is quitechallenging. This paper emphatically explained the effect of the ionic assosiacted states oftertiary amine based monomers in acidic aqueous media on their kinetics of visible lightactivated room-temperature RAFT polymerization. For this purpose, the tertiary amine basedmonomer the N-(3-(dimethylamino)propyl)acrylamide (DMAPAA), the water soluble chaintransfer agent3-(2-(ethylthiocarbonothioylthio)-2-methylpropanamido)-N,N,N-trimethylpropan-1-aminium iodide (EMTAI), and photoinitiator sodium phenyl(2,4,6-trimethyl-benzoyl) phosphinate (SPTP) were synthetized in this papers. The visible light absorption ofthe chain transfer agent and photo-initiater were obvious, and sufficient to visible lightactivated aqeouse RAFT polymerization. The ionic associated states of this monomer weremodulated by changing counter ions, monomer concentration. The results of the studydemonstrated that in higher initial monomer concentrations, the polymerazition of DMAPAAwas very fast and high-efficiency, in just twenty minutes, the conversion reached ninetypercent. Diluting the solution would slow down the apparent rate constant of polymerization.Moreover, at [DMAPAA-Cl-]0≤1.0mol L-1, the semi-logarithmic kinetic curves separatedinto two stages, i.e. linearly evolved at the early stage up to a critical monomer conversions.The results of GPC traces and UV-vis spetra demonstrated the chain transfer agent did notdegrade and chain transfer equilibrium did not shift. In the same conditions, thepolymerization of N-isopropylacrylamide (NIPAM) did not show the deviate of thesemi-logarithmic kinetic curves.Then we deduced that it was the protonation of DMAPAAthat make it show different kinetic curves compared with NIPAM. Replacing the chloridecounter-ions (DMAPAA-Cl-) with the larger BF4-or CF3SO3-counter-ions resulted in a morerapid polymerization process in the dilute solution. Also, the semi-logarithmic kinetic curvesbecame linear using CF3SO3-as counter-ions. These unique behaviours were attributed to theion association of monomer and counter-ions, which led to the local enrichment of monomersand partially shielding the electrostatic repulsion of ionized monomers and growing chains.