Effect of Hofmeister Salts on the LCST of Poly(diethyl vinylphosphonate) and Poly(2‐vinylpyridine‐block‐diethyl vinylphosphonate)

Abstract

AbstractHerein, the effect of Hofmeister anions on the cloud point of poly(diethyl vinylphosphonate) (PDEVP) homopolymers and poly(2‐vinylpyridine‐block‐diethyl vinylphosphonate) (P(2VP‐b‐DEVP)) block copolymers using their sodium salts is reported. The change in the cloud point temperature (TCP) of these two polymers upon the addition of coordinating transition metal salts is investigated. The TCP of the different solutions is determined by ultraviolet–visible spectroscopy at different temperatures. Additionally, dynamic light scattering (DLS) is applied to investigate the behavior of the block copolymer below and above the TCP. Both polymers follow the trend of the Hofmeister series using the different sodium salts. This indicates that the P2VP block of the copolymer does not affect the TCP when noncoordinating cations are used. In contrast, a linear increase in the TCP is observed when the block copolymer is used in the presence of copper(II) or iron(III), whereas the TCP of the homopolymer in the same concentration range remains unchanged. The cloud point is increased due to an increase in hydrophilicity and electrostatic repulsion, resulting from the transition metal ion coordination. The coordination to the P2VP units is confirmed by the DLS. These findings can lead to potential applications as sensors or in wastewater purification.