Aqueous solutions of amphiphilic polymers often undergo a reversible heat-induced phase separation. In the case of aqueous poly(2-isopropyl-2-oxazoline) (PIPOZ) solutions, the phase separation is followed, upon prolonged heat treatment, by an irreversible crystallization of the polymer.  Vibrational spectroscopy studies combined with molecular orbital (MO) calculations and spectral measurements with model compounds indicate that PIPOZ chains heated above the phase transition temperature undergo a conformational transition to a more stable conformer.1  This change, which is irreversible upon cooling the solution below Tc, leads to the conformation taken by the polymer in the crystalline phase. Polymer crystallization ensues via a nucleation/growth mechanism.A corollary of this observation would be that if the PIPOZ chains are �frozen� in cold water in conformations unfavorable to crystallization, the heat-induced phase transition of their solutions should be fully reversible.  I will describe various situations where the PIPOZ chain conformation in cold water was engineered in order to foil crystallization.  Schematic representation of the conformational changes of PIPOZ in water as a function of solution temperature 1. Katsumoto, Y et al. Macromolecules 2012, 45, 3531-3541.

Thoughts on the interplay between the conformation of poly(2-isopropyl-2-oxazoline) chains in solution and their ability to crystallize from hot water

248th National Meeting (2014)

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