## 1 Introduction
[29] studied styrene polymerization, but the affinity between the polymer and silica nanoparticles was provided by electrostatic interactions. In another study, [PERSON] et al. [28] performed Pickering emulsion polymerization of styrene stabilized by vinylsilane-functionalized montmorillonite platelets, which resulted in hetero-coagulation nucleation of latex particles. At the early stage of the reaction, they observed fast formation of primary polymer particles by hetero-coagulation, due to attractive interactions between styrene and the surface-functionalized clays. In contrast, several works have reported that micellar mechanisms can occur, in some experimental conditions, when inorganic nanoparticles' aggregates form pseudoc micelles in the aqueous phase that lead to an increase in the solubility of the hydrophobic monomers [1; 29; 35; 40]. The monomers react with radicals, originated from the hydrophilic initiator thermal decomposition, where the pseudo-micelles provide stability to the oligomers, thus limiting their coagulation. The subsequent primary particles formed are then swollen by monomers to finally form latex particles. From the above-mentioned examples, it is clear that designing hybrid materials with specific properties requires a good understanding of the mechanistic events that occur during the polymerization. However, suitable modifications or functionalization of the inorganic nanoparticles are usually required to favor the interactions between the inorganic nanoparticles with monomers or the polymer matrix, directly involving the inorganic nanoparticles in the polymerization mechanisms. Moreover, it is noteworthy that hypercrosslinked polymer microspheres with regular shape and high sorption capacities are required for diverse applications such as high-performance chromatography, ion exchange, hydrogen storage, and water treatment [41; 42]. Dispersion polymerization has been reported to be a suitable method for preparing monodisperse micrometric polymer particles through a one-pot reaction, where all the ingredients are mixed and heated at the initial charge [43]. However, this process becomes troublesome and challenging when preparation of hypercrosslinked microspheres is required [43; 44]. Indeed, the presence of a bifunctional monomer as a crosslinking agent modifies the size, morphologies, and size distribution of the final microspheres because it interferes with the nucleation and growth step [45; 43; 44]. A number of investigations have pointed out the difficulties in obtaining monodisperse hypercrosslinked particles. Several works have reported some improvements in this situation but without offering a full solution [43]. Similarly, Pickering emulsion polymerization can represent an alternative for preparing hypercrosslinked polymer particles, and some studies have reported the preparation of hypercrosslinked Styrene-Co-Dvinylbenzene (St-co-DVB) nanospheres by using surface-modified titania hydrosols [46; 47]. Nonetheless, the reactions were performed with less than 4 wt% polymer contents by using a relatively high amount of flocculated titania nanoparticles. The preparation of the St-co-DVB core-shell nanospheres was based on a pseudo-micellar nucleation mechanism. In this study, St-co-DVB polymerizations were performed in the presence of cationic silica nanoparticles (SNPs) and sodium 4-vinylbenzenesulfonate (VBS), as a co-aid and functionalizing agent, in emulsions with basic and acidic water-phase conditions. The objective was to obtain a broad view of the mechanistic events that can occur during the different intervals of Pickering emulsion polymerization, depending on the interactions between SNPs with monomers or the polymer. Indeed, based on only one Pickering emulsion formulation, different polymerization mechanisms can occur, depending on the nature of the SNPs as Pickering agents. This, in turn, directly depends on the emulsion pH and especially VBS as an SNp-functionalizing agent.