Well-Defined Multi-Amino-Functional and Stimuli-Responsive Poly(propylene oxide) by Crown Ether Assisted Anionic Ring-Opening Polymerization

Multi-amino-functional poly(propylene oxide) (PPO) copolymers were synthesized by the anionic ring-opening copolymerization (AROP) of N,N-diethyl glycidyl amine (DEGA) and propylene oxide (PO). A solvent free synthesis route using potassium counterions and crown ether for the AROP enabled controlled (co)polymerization with full conversion. The strategy provided access to PPO-b-PDEGA block copolymers, statistical PPO-co-PDEGA copolymers, and, for the first time, PDEGA homopolymer. Molecular weights in the range of 1400 to 4200 g/mol (M-n) and dispersities (M-w/M-n) below 1.1 were obtained. Both the kinetics and resulting microstructure of the statistical copolymerization were investigated by in situ H-1 NMR spectroscopy, revealing reactivity ratios of r(PO) = 1.7 and r(DEGA) = 0.9. The polyethers exhibit thermoresponsive behavior in aqueous solution, showing cloud points in the range 14-57 degrees C under neutral conditions. Because of the amine groups, the copolymer structures are strongly affected by the pH of the solution, and therefore the cloud points are highly pH-dependent. By changing the pH of the polymer solution, the cloud points can be tuned between 5 and 100 degrees C, as studied by turbidity measurements. The copolymers offer new potential for PPO-based structures for surface modification, biomedical purposes and pharmaceutical application.