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Lower critical solution temperature sensitivity to structural changes in poly(N‐isopropyl acrylamide) homopolymers

García‐Peñas, Alberto, Wang, Yu, Muñoz‐Bonilla, Alexandra, Fernández‐García, Marta, Stadler, Florian J.
Journal of polymer science 2019 v.57 no.20 pp. 1386-1393
acrylamides, calorimetry, molecular weight, polymers, rheology, temperature
The effect of the molecular weight on the lower critical solution temperature (LCST) has been discussed extensively, where LCST increased with molar mass, decreased or kept constant, which leads to confusion. This work is focused on the preparation of poly(N‐isopropyl acrylamide) homopolymers, obtained in a wide molecular weights range. The LCST behavior is analyzed by calorimetry and rheology, and a deep study of molecular features is carried out for a better knowledge of the influence of various parameters involved on LCST. Finally, the molecular weight trend is observed, and its influence on LCST is compared with the effect of other parameters as polymer concentration in water, end‐group effect, and tacticity. It is observed that other parameters such tacticity and end‐group effect will affect the LCST behavior over molecular weight, if this one is not high enough. Furthermore, the study of the LCST ranges will be a useful tool for analyzing the molecular weight trends. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1386–1393