## 3 Polymerization Reactions within AAO Templates
### ATRP Polymerization  
Atomic transfer radical polymerization (ATRP) has been also used for the synthesis of different polymers and copolymers. The possibility of combining AAO templates with controlled/\"living\" radical polymerization techniques leads to more controlled polymerization systems. In the following section, some representative examples are reported chronologically. ATRP copolymerization of NIPAM-co-MBAA. [PERSON] et al. studied, for the first time, the synthesis of thermosensitive Poly(\(N\)-isopropylacrylamide)/\(N\),\(N^{\prime}\)-methylenebisacrylamide (PNIPAM-co-MBAA) nanotubes by atom transfer radical polymerization within AAO porous membranes [137]. The ATRP polymerization of NIPAM-co-MBAA copolymer was surface-initiated on aminosilane surface-modified porous anodic aluminum oxide membrane as shown schematically in Figure 11. The copolymerization was successful and led to polymer nanotubes with high thermosensitive behavior. Moreover, in an aqueous environment, AFM studies in real time revealed that changes in the temperature induced changes in the dimension and shape of the nanotubes, i.e., upon heating to LCST or above, the nanotubes underwent a shape alteration from elliptical to circular in water. The same authors also studied the synthesis of PNIPAM-co-MBAA copolymers with various copolymer compositions [138] and the influence of monomer concentration on the size of nanotubes. Through SEM, TEM, AFM, and GPC measurements, the authors showed that an increase in the monomer concentration in the polymerization system was followed by a proportional increment of thickness of the nanotubes. Figure 10: Conversion versus time of polyurethanes polymerized in bulk, as well as in 35, 60 and 140 nm pores at 80 \({}^{\circ}\)C. Symbols indicate experimental data, and solid and dotted lines show diffusion (Dif) and no diffusion (NoDif) model predictions ([136]). Copyright 2018. Reproduced with permission from the publisher: Elsevier. In the following sections, the ATRP polymerization and copolymerization of a series of monomers are also reported [60; 138; 139; 140; 141; 142]  
ATRP Polymerization of MMA. [PERSON] et al. studied the polymerization of methyl methacrylate by surface-initiated polymerization [60] and the effect of substrate geometry on the polymer molecular weight and dispersity when chains were grown on anodically etched aluminum oxide (AAO) substrates via surface-initiated atom transfer radical polymerization. The cleavage of chains from the substrates using hydrogen fluoride was evidenced by the evolution of Si-OH, C-H, C=O and Si-O bands from infrared spectroscopy. The authors found that PMMA grown on AAO substrates had a much lower molecular weight and a broader molecular weight distribution than polymer grown in solution, and they proposed that confinement effects imposed by the pores during the polymerization would reduce growth rates and increase the polydispersity of chains. Moreover, [PERSON] et al. studied [143] a modified sol\(-\)gel technique to continuously vary the pore diameters in porous alumina templates by means of ATRP grafting of PMMA, and [PERSON] et al. studied the surface-initiated ATRP polymerization of acrylic acid on dopamine-functionalized AAO membranes [141]. ATRP Polymerization of NIPAM. [PERSON] et al. [140] prepared a series of thermo-responsive \"gating\" membranes with controllable length and density by grafting poly(N-isopropylacrylamide) (PNIPAM) chains onto the pores of AAO membranes by atom-transfer radical polymerization (ATRP) mechanisms. First, they immobilized 3-aminopropyl)triethoxysilane (APTES) on the AAO nanopores. This was followed by post-modification with the initiator 2-bromoisobutyryl bromide (BIBB) and the subsequent polymerization of NIPAM from the surface. The effect of grafting temperature and time, the feed concentration of NIPAM and the density of \(-\)Br on the grafting yields of AAO-\(g\)-PNIPAM membranes was studied in order to control the thermo-responsive efficiency of AAO-\(g\)-PNIPAM gating membranes.