Why does UREA (cas 506-89-8) have a different effect on the collapse temperature of PDEAM and PNIPAM?

Add time:07/18/2019    Source:sciencedirect.com

The two polymers poly(N,N-diethylacrylamide), PDEAM, and poly(N-isopropylacrylamide), PNIPAM, undergo a coil-to-globule collapse transition in water on increasing the temperature. The process is endothermic and it is driven by the gain in translational entropy of water molecules due to the decrease in solvent-excluded volume associated with the transition from swollen to globular conformations of the polymer. Curiously, in the presence of UREA (cas 506-89-8), the two polymers have a different behaviour: globular conformations are stabilized for PNIPAM, while swollen conformations are stabilized for PDEAM [Macromolecules 49 (2016) 234]. Here, we present an application of the theoretical approach already used to rationalize several aspects of PNIPAM collapse [Phys. Chem. Chem. Phys. 17 (2015) 27750; Phys. Chem. Chem. Phys. 18 (2016) 14426]. This model is able to provide a reliable explanation for the different behaviour of urea towards PDEAM and PNIPAM. The difference might be in fact due to the number of urea-polymer contacts that is larger in the case of PDEAM with respect to PNIPAM for the presence of two extra methylene groups in each side chain of the former polymer.

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