Thermoresponsive polymers as macromolecular coordination ligands: complexation-dependence of thermally induced aggregation in aqueous solution

We have designed novel macromolecular coordination ligands (MCLs) by conjugation of thermoresponsive polymers based on poly(N-isopropylacrylamide) (n around 3 to 25 kg mol−1) with 1,2,4-triazole coordination sites. These triazole units were integrated into two fundamentally different MCL architectures via reversible addition–fragmentation chain transfer polymerization following two synthetic strategies: (I) The customized chain transfer agent 1-{[3-(4H-1,2,4-triazol-4-yl)propyl]amino}-2-methyl-1-oxopropan-2-yl dodecyl carbonotrithioate (DMP-APTRZ) was employed for hemi-telechelic MCLs with a single triazole end group. (II) A tailored comonomer N-[3-(4H-1,2,4-triazol-4-yl)propyl]methacrylamide (APTRZMAAm) provides access to multidentate MCLs with a controllable number of triazole side groups along the polymer backbone. The thermally controlled variation of the MCL volume demand in aqueous solution was exploited for reversible aggregate formation upon Fe2+ complexation. Thermal response was studied via UV/Vis turbidity measurements, aggregate dimensions were determined via DLS, while the aggregate morphology was analyzed via customized TEM.