Study of the Thermal Phase Transition of Poly(N,N-diethylacrylamide-co-N-ethylacrylamide) Random Copolymers in Aqueous Solution

Author:

Coca-Hidalgo José Javier1ORCID,Recillas-Mota Maricarmen1ORCID,Fernández-Quiroz Daniel2ORCID,Lizardi-Mendoza Jaime1ORCID,Peniche-Covas Carlos3ORCID,Goycoolea Francisco M.4ORCID,Argüelles-Monal Waldo M.1ORCID

Affiliation:

1. Centro de Investigación en Alimentación y Desarrollo, Hermosillo 83304, Mexico

2. Departamento de Ingeniería Química y Metalurgia, Universidad de Sonora, Hermosillo 83000, Mexico

3. Facultad de Química, Universidad de La Habana, La Habana 10400, Cuba

4. School of Food Science and Nutrition, University of Leeds, LS2 9JT Leeds, UK

Abstract

N-alkyl-substituted polyacrylamides exhibit a thermal coil-to-globule transition in aqueous solution driven by an increase in hydrophobic interactions with rising temperature. With the aim of understanding the role of N-alkyl substituents in the thermal transition, this study focuses on the molecular interactions underlying the phase transition of poly(N,N-diethylacrylamide-co-N-ethylacrylamide) random copolymers. Poly(N,N-diethylacrylamide) (PDEAm), poly(N-ethylacrylamide) (PNEAm), and their random copolymers were synthesized by free radical polymerization and their chemical structure characterized spectroscopically. It was found that the values of the cloud-point temperature increased with PNEAm content, and particle aggregation processes took place, increasing the negative charge density on their surface. The cloud-point temperature of each copolymer decreased with respect to the theoretical values calculated assuming an absence of interactions. It is attributed to the formation of intra- and interchain hydrogen bonding in aqueous solutions. These interactions favor the formation of more hydrophobic macromolecular segments, thereby promoting the cooperative nature of the transition. These results definitively reveal the dominant mechanism occurring during the phase transition in the aqueous solutions of these copolymers.

Publisher

MDPI AG

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