## 1 Introduction  
Nanocomposite materials containing noble metal and dispersed nanoparticles in a polymer matrix may exhibit peculiar physical and chemical properties that are of high scientific and technological importance [1]. These new composites are used for optical [2], electrical [3] and medical [4] applications as well as data storage [5]. In particular, silver nanoparticles are very important for their excellent electrical conductivity [6], anti-microbial effect [7] and optical properties [8]. In recent years, a whole bunch of synthetic methods for the preparation of metal nanoparticules have been developed: chemical, photochemical and thermal. Metal-polymer nanocomposites are usually obtained via multistep methods. Dry silver nanoparticules (NPs) produced beforehand can be dispersed into a polymerizable formulation to obtain self-assembly functionalized structures. However, besides the specific hazards related to handling dry NPs, their size dispersity over a large scale is difficult to control, thus limiting the interest of this \"_ex situ_\" method [9,10]. The \"_in situ_\" approach that involves the generation of metal nanoparticules directly in a polymerizable medium through reduction of cationic precursors offers the advantages of better dispersion ability and facile chemical or photochemical reduction [11,12]. Thermally and photochemically induced free radical polymerizations (FRP) have been the subject of numerous studies [13, 14, 15, 16, 17, 18]. In thermal FRPs, redox initiated processes are very attractive due e.g., to the absence of solvents and the use of quite low reaction temperatures. However, such FRPs suffer from a strong drawback concerned with the well-known oxygen inhibition [13, 14, 15, 16, 17, 18, 19, 20]. Indeed, both the initiating (Scheme 1(r1)) and propagating (Scheme 1(r2)) radicals are scaved by O\({}_{2}\) and converted into stable peroxyl radicals, which cannot participate in any further polymerization initiation reactions and lead to a decrease of both polymerization rates and final conversions (Scheme 1) [21, 22, 23, 24]. **Scheme 1. ** Different polymerization reactions under oxygen (r1: initiating step and r2: propagation step). In cationic polymerization (CP), such an inhibition does not exist and, interestingly, the use of less toxic monomers than the acrylates can be highly worthwhile. Redox systems being able to initiate a cationic polymerization have been already proposed [25, 26, 27, 28]. Very recently, new bi-component combinations based on onium salt (diaryliodonium or triarylsulfonylium salt) and organosilane (R\({}_{3}\)SiH) as the reducing agent were elegantly proposed: the redox reaction is catalyzed by noble metal complexes (platinum, palladium, rhodium) and leads to a silylium cation, which directly attacks the epoxide or/and reacts with water to form a Bronstedt acid [29]. The thermal FRP and/or CP at room temperature and under air remain an exciting research topic. This approach consists of producing a radical R\({}^{\bullet}\) (from an organosilane), to initiate FRP, that can be easily oxidized by a silver salt (e.g., AgSbF\({}_{6}\)) leading to R\({}^{+}\), which corresponds to the ROP initiating structure (Scheme 2) [30; 31; 32]. However, the nature of the primary radicals produced from the organosilane is crucial for getting a high polymerization efficiency, as they should be characterized by excellent oxidation properties; moreover, the resulting radicals and cations must be efficient structures for the FRP and CP reactions, respectively [33; 34; 35; 36; 37]. Even if a lot of systems have been developed in the last years [33; 34; 35; 36; 37; 38; 39; 40; 41; 42], the search for novel additives being able to improve the radical and/or cationic polymerization processes still appears as a challenge. In the present paper, _N_-vinylcarbazole (NVK) is used as an additive for thermal free and/or cationic polymerization of an acrylate and an epoxide at room temperature and under air (TMPTA, St and EPOX--see below, Scheme 3).