A Solventless Melt Route to Polymer/Mixed‐Metal Sulfide Nanocomposites: Case Study on <scp> NiCo ₂ S ₄ </scp> / <scp>PVP</scp>

ABSTRACT Polymer‐inorganic nanocomposites are commonly prepared using solution‐based approaches that rely on solvents, often toxic or costly, and multi‐step processing, which can limit scalability, environmental compatibility, and interfacial control. The development of solvent‐free synthetic strategies that enable controlled nanoparticle formation directly within polymer matrices, therefore, remains an important challenge. Here, we demonstrate a solventless melt approach for the in situ synthesis of NiCo 2 S 4 /polyvinylpyrrolidone (PVP) nanocomposites via thermolysis of metal xanthate precursors, where the polymer melt simultaneously acts as the reaction medium and a stabilizing matrix for nanoparticle formation. Crystalline NiCo 2 S 4 nanoparticles (4–12 nm) are formed uniformly within the polymer matrix, with particle size governed primarily by polymer concentration and precursor alkyl chain length. Higher PVP content effectively restricts crystal growth, while longer‐chain precursors promote larger crystallites, with short‐chain precursors yielding more uniform nanoparticle dispersion, indicating that polymer‐precursor interactions play a key role in nanostructure evolution. Spectroscopic analysis suggests coordination between PVP carbonyl groups and the NiCo 2 S 4 surface contributing to controlled dispersion and reduced agglomeration. This work establishes, for the first time, a solventless melt strategy for the preparation of mixed‐metal sulfide/polymer nanocomposites, providing a scalable and environmentally benign route to polymer‐inorganic hybrid materials. While the present study focuses on structure–morphology relationships, the resulting nanocomposites are of potential interest for applications in energy storage, electrocatalysis, and sensing. The applicability of this approach is governed by the thermal compatibility between precursor decomposition and polymer stability, highlighting important considerations for extending this strategy to other systems.