Phase Transition Kinetics of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

• Published in: Macromolecules Vol. 53; no. 8; pp. 2841 - 2855
• Main Authors: Kreuzer, Lucas P, Widmann, Tobias, Bießmann, Lorenz, Hohn, Nuri, Pantle, Johannes, Märkl, Raphael, Moulin, Jean-François, Hildebrand, Viet, Laschewsky, André, Papadakis, Christine M, Müller-Buschbaum, Peter
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28-04-2020
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c00046

The swelling and phase transition behavior upon increasing temperature of a doubly thermoresponsive diblock copolymer thin film in steps above the characteristic cloud points (CPs) of the blocks is studied. An upper critical solution temperature (UCST)-type zwitterionic poly­(sulfobetaine), poly­(N,N-dimethyl-N-(3-methacrylamidopropyl)-ammoniopropane sulfonate) (PSPP, CPUCST = 31.5 °C), is combined with a lower critical solution temperature (LCST)-type nonionic poly­(N-isopropyl-/methacrylamide) (PNIPMAM, CPLCST = 49.5 °C) block. Using time-of-flight neutron reflectivity (ToF-NR), we observe the swelling in D2O vapor at a constant temperature of 20 °C, followed by two subsequent temperature jumps, from 20 to 40 °C (above CPUCST) and from 40 to 60 °C (above CPLCST). The observed response of the diblock copolymer films deviates from the aqueous solution behavior, which is mainly attributed to the increased polymer concentration. Temperature-induced changes in the thin-film nanostructure are investigated with ToF grazing-incidence small-angle neutron scattering (GISANS). Alterations in the chain conformation and hydrogen bonding are probed by Fourier transform infrared (FTIR) spectroscopy. The ionic SO3 – groups (in the PSPP block) and the nonionic hydrophilic amide groups (in both blocks) are found to affect the mechanisms of D2O uptake and release significantly.