Study of the temperature-induced aggregation of polyoxometalate-poly( N,N -diethylacrylamide) hybrids in water

In this article, we study the temperature-induced phase transition of aqueous solutions of tailor-made Dawson polyoxometalate-poly(N,N-diethylacrylamide) hybrids (POM-PDEAAm) by means of differential scanning calorimetry, dynamic light scattering and cryo-TEM microscopy. Generally, the typical thermoresponsive aggregation of the PDEAAm in water was transferred to the hybrids. The organization of the compounds in solution below and above the transition temperature was studied, and precious insights in the aggregation mechanisms were obtained. The impact of the polymer chain-ends, the nature of the counterions of the negatively charged POM subunits and the weight fraction of the POM was elucidated, revealing a strong influence of the POM's counter-ions. Temperature and nature of the cations are thus two external factors that can be used to control the properties of the conjugates.