## 3 Polymerization Reactions within AAO Templates
### Electrochemical Polymerization  
The first work of electrochemical polymerization reactions in AAO nanocavities was reported by [PERSON]'s group in 1990 [1], although it may be noted that this work was preceded in 1986 by their work on the synthesis and morphological control of electronically conductive polymers in nucleopore polycarbonate membranes [2; 58]. Due to the interest of their electronic/physical properties and potential application in electronics devices, this work was later extended to the synthesis of \(\pi\)-electron conjugated polymers. This section briefly summarizes a selection of the work relating to such conjugated polymers including polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT) as well as their copolymers. In the majority of these studies, the nature of the polymerization mechanism is not actually referred to. In fact, electropolymerization reactions resemble the electrodeposition reaction of metals, although it is far from being understood and generalized, even taking into account the great amount of works reported in the literature, from the 1 st Handbook edition on conjugated polymers: properties, processing, and applications [104], to the last one [105]. In the 1990s, [PERSON] et al. studied the electrochemical polymerization of various ionic monomers under different polymerization and template conditions. In particular, they studied different types of heterocycle monomers, the monomer concentration, the nature of the oxidant and concentration, the polymerization temperature, the reaction time and solvent type. Over the course of this work, they optimized the procedure and adopted a general template-based protocol for the preparation of nanomaterial [106]. The electrochemical synthesis of poly(N-methylpyrrole) nanotubes was first carried out within microporous polycarbonate membranes available in a variety of diameters from 30 to 800 nm, under various polymerization and templates conditions [27; 61; 107; 108]. It was observed that if monomers were polymerized within the nanopores, it was possible to adjust the wall thickness of the resulting polymer by choosing the right polymerization conditions, mainly the polymerization time. Thus, nanotubes with thin walls (at short polymerization times) or thick walls (at long polymerization times) could be obtained, see Figure 3. What they proposed was that for polypyrrole, the nanotubes ultimately \"close up\" to form solid fibrils. Hence, by controlling the polymerization time, it was possible to make hollow polypyrrole nanotubes or solid fibrils. In addition, by polarized infrared absorption spectroscopy, [PERSON] and co-workers observed that the polymer chains of materials synthesized in the narrowest template were oriented and the conductivity of confined polypyrrole was significantly enhanced. They proposed that the preferential orientation of polymer chains was partially responsible for the observed enhancement in conductivity. Also related to the synthesis of PPY, some years later, [PERSON] et al. [109] studied the electrochemical polymerization of PPY inside AAO nanopores in order to obtain polypyrrole nanotubes. The authors observed the presence of hollow nanotubes by SEM and suggested that PPY initially deposited on the surface of the pore walls. Moreover, analysis of the membrane surface showed that the nanopores were not completely filled and that they did not stick out of the membrane even after increasing the polymerization time and voltage. The formation of the polymer was confirmed, while the increasing of the conjugation length was observed as a consequence of vibration restrictions caused by the confined environment where the polymer was located. Building on this work, [PERSON] et al. [110] studied the chemical polymerization of acid-functionalized (COOH) PPY-containing oxidizable monomers using AAO membranes in liquid phase polymerization conditions.