Effect of DMAPAA Copolymerization on Fe 3 O 4 Nanoparticle Formation, Magnetic Heating, and Adsorption Behavior in Thermoresponsive PNIPAm Gels

ABSTRACT Thermoresponsive magnetic composite gels based on poly( N‐ isopropylacrylamide) (PNIPAm) and its copolymers with N,N ‐dimethylaminopropylacrylamide (DMAPAA) were prepared by in situ formation of Fe 3 O 4 nanoparticles within the gel matrices. DMAPAA was introduced as a hydrophilic comonomer to improve the swelling stability of PNIPAm gels in concentrated iron ion solutions and to investigate its effect on nanoparticle formation, crystallite size, magnetic heating behavior, and adsorption properties. Pure PNIPAm gels exhibited severe deswelling in iron ion solutions due to the salting‐out effect, resulting in low magnetite content (5.9 wt%). In contrast, copolymerization with DMAPAA significantly improved gel swelling stability, increasing the Fe 3 O 4 content to 9.5 and 14.2 wt% for NIPAm/DMAPAA compositions of 900/100 and 800/200 mol/m 3 , respectively. XRD analysis confirmed the formation of magnetite nanoparticles (MNPs) with crystallite sizes of 9.4–11.1 nm. TEM observations revealed more uniformly dispersed MNPs with well‐defined morphologies in the copolymer gels compared with pure PNIPAm gels. Magnetic heating experiments under an alternating magnetic field demonstrated that the temperature rise increased with increasing magnetite content, while the thermoresponsive behavior of PNIPAm was preserved after nanoparticle formation. The copolymer gels exhibited broader and more gradual volume transitions because of the increased hydrophilicity introduced by DMAPAA. Bisphenol A (BPA) adsorption experiments demonstrated temperature‐dependent adsorption behavior associated with the hydrophilic–hydrophobic transition of PNIPAm. However, increasing DMAPAA content reduced BPA adsorption because of the enhanced hydrophilicity of the copolymer network. These results demonstrate that DMAPAA copolymerization is an effective strategy for controlling MNP incorporation and magnetic heating performance while maintaining thermoresponsive properties.