Polymer Nanoparticles: A New Technological Platform for Emerging Applications

Polymer-based nanoparticles tackle many different fields, from extrinsic self-healing materials to cosmetics, from electronics to nanophotonics. This is mainly due to the wide range of applications and market needs that polymers have been satisfying since their discovery. Moreover, polymer nanoparticles in the submicrometric dimensional range have been obtained by different methods. However, the scientific community is still debating whether bulk polymer properties are retained in this nanostructures or not. In this work, a method for the in-situ monitoring of polymer chains aggregation state within polystyrene nanoparticles (NPs) based on the time-resolved fluorescence of a tailored molecular rotor was developed. Differently from previous literature, this technique was calibrated and compared with standard differential scanning calorimetry, in order to have a replicable and robust standard reference. The results leaded to the conclusion that bulk polymer properties related to glass transition are conserved even in nanoparticles of some tens of nm in radius. This observation was used as an important paradigm towards the preparation and application of biphasic polymer-based nanoparticles. With this regard, an optimized semicontinuous emulsion polymerization protocol for the preparation of Poly(n-Butyl Acrylate)@Polystyrene (PBA@PS) core@shell NPs was developed. These nanostructures were found to behave as force-responsive nano-objects, leading to the first example of baroplasticity detected on a single particle scale. Beyond the basic research interest on the nanomorphology evolution under non-equilibrium stress, this result can be interesting in manufacturing a new class of sealing nanoadditives in the field of extrinsic self-healing materials. We demonstrated that PBA@PS NPs can have even other applications. Namely, PBA@PS nanoparticles were used as nanocontainers for lipophilic derivatives of a bio-compatible dye and as nanoemitters for sensitized up-conversion (SUC). In order to overcome some SUC limits of PBA@PS NPs, liquid-core nanocapsules composed by a n-hexadecane (HD) core embedded in a plastomer poly(methyl methacrylate) (PMMA) shell were prepared. The preparation protocol of such nanocapsules was optimized in order to use them as nano-additives to be delivered within self-standing Proof-of-Concept polymer materials. Particularly, a poly(vinyl alcohol) bulk SUC film was prepared and found to be effective even in ambient conditions, demonstrating the potentialities of this system for everyday-applications. Besides, HD@PMMA nanocontainers were used for encapsulating oxide nanocrystals for the preparation of hybrid polymer materials with enhanced refractive index. The nano-oxide loading within the HD core was so high to inhibit either the crystallization of HD and the aggregation of the nanocrystals. Thanks to these capabilities, the oxide-loaded nanocapsules have been used during the bulk polymerization of MMA, obtaining a bulk sample of PMMA with improved refractive index and naked eye transparency. Concluding, examples about the applicability of polymer nanoparticles as smart additives within formulations for the preparation of hierarchical functional materials in the contest of a more sustainable chemistry for materials science applications are devised in this work.