Citation

Lan Ma, and Peiyi Wu*. The Role a Unique Spatial Structure Plays in the Volume Phase Transition Behavior of Poly(N-Isopropylacrylamide)-Based Interpenetrating Polymer Network Microgel Including a Thermosensitive Poly(Ionic Liquid). Phys. Chem. Chem. Phys. 2018, 20, 8077-8087 

Abstract

Well-defined poly(N-isopropylacrylamide)/poly(tributylhexylphosphonium 3-sulfopropylmethacrylate) (PNIPAM/P[P4,4,4,6][MC3S]) interpenetrating polymer network (IPN) microgels were synthesized by a two-step precipitation polymerization, and the thermally induced phase transition mechanism of IPN microgels was investigated by using dynamic light scattering (DLS), temperature-dependent IR spectroscopy together with perturbation correlation moving window (PCMW) technique and two dimensional correlation spectroscopy (2Dcos). For comparison, PNIPAM/P[P4,4,4,6][MC3S] polymer mixture was also studied to reveal the influence of complex spatial network of IPN on the thermoresponsive behavior. Due to the strong hydrophilic feature of P[P4,4,4,6][MC3S] and special IPN structure, PNIPAM and P[P4,4,4,6][MC3S] moieties exhibited different phase transition tendency during heating. In detail, the dehydration behavior of PNIPAM part seemed gradual and continuous while that of ester C=O in P[P4,4,4,6][MC3S] part became sharp. While the two components just dehydrated independently and successively in the polymer mixture without any mutual interaction. The collapse of P[P4,4,4,6][MC3S] network at the second transition stage boosted the increase in the amount of intramolecular hydrogen bond (amide C=O···D-N) in PNIPAM moiety. Additionally, electrostatic interaction of P[P4,4,4,6][MC3S] network played a non-ignorable role to enhance the swelling property of PNIPAM/P[P4,4,4,6][MC3S] IPN microgels.