Customizing Polymers by Controlling Cation Switching Dynamics in Non-Living Polymerization

Controlling the chain growth process in non-living polymerization reactions is difficult because chain termination typically occurs faster than the time it takes to apply an external trigger. To overcome this limitation, we have developed a strategy to regulate non-living polymerizations by exploiting the chemical equilibria between a metal catalyst and secondary metal cations. We have prepared two nickel phenoxyphosphine–polyethylene glycol variants, one with 2-methoxyphenyl (Ni1) and another with 2,6-dimethoxyphenyl (Ni2) phosphine substituents. Ethylene polymerization studies using these complexes in the presence of alkali salts revealed that chain growth is strongly dependent on electronic effects, whereas chain termination is dependent on both steric and electronic effects. By adjusting the solvent polarity, we can favor polymerizations via non-switching or dynamic switching modes. For example, in a 100:0.2 mixture of toluene/diethyl ether, reactions of Ni1 and both Li+ and Na+ cations in the presence of ethylene yielded bimodal polymers with different relative fractions depending on the Li+/Na+ ratio used. In a 98:2 mixture of toluene/diethyl ether, reactions of Ni2 and Cs+ in the presence of ethylene generated monomodal polyethylene with dispersity