## 5 General Discussion and Conclusions  
Significant effort has been devoted to developing in situ polymerization reactions in AAO templates and in other nanoporous hard materials of different geometries (non-reported in the present review). The vast majority of reported works have addressed either the influence of spatial confinement on the polymerization process, in particular, on reaction kinetics and molecular weight of the synthesized polymer or have sought to obtain polymer nanostructures with modulated properties. Free radical, step-growth and  
Figure 14: SEM image of an osteoblastic cell on \(\beta\)-Ketonitrile tautomeric copolymer nanowires [168], Copyright 2015. Reproduced with permission from the publisher: Elsevier. ATRP polymerizations are the most studied polymerization reactions. Although some of the reported results are contradictory and do not seem to follow a general trend, even for the same template or reaction mechanism, some general conclusions can be drawn:  
Constrained AAO geometries as well as mesoporous silica templates, porous controlled pore glasses and metal-organic framework can be considered as nanoreactors for the polymerization reactions in order to obtain polymer nanostructures directly from the precursor monomer. Polymerization reactions in nanopores tend to yield a high degree of conversion with higher rates than the comparative reaction in bulk polymerization. In many cases, it reaches near 100% conversion. Experiments of polymerization in confinement show that each system is different, and depends on the mechanism of polymerization process--radical polymerization, polycondensation, or other mechanism--and on the porous material--AAO templates, mesoporous silica, controlled pore glass nanopores, etc. The Tg of the polymers synthesized in confinement are in general higher than their bulk counterparts. Nevertheless, the molecular weight does not follow a general rule, and both higher and lower values have been reported compared to the bulk. Although the present review only refers to AAO templates, the comparison with other confining media is not trivial, as the degree and the geometry of confinement exerted in by each system is different. For example, while AAO templates can be considered isolated nanoreactors, the nanopores in CGP are interconnected. For this reason, general conclusions for nanopolymerization reactions are difficult to drawn. Anodized aluminum oxide (AAO) templates present some advantages for studies of polymerization reaction. For instance, the kinetics of polymerization reaction in confinement can be monitored in situ. Confinement impacts free radical polymerization, yielding lower molecular weights and dispersity values. In some cases, polymerization within the AAO template favors the polymer stereoregularity. Modelling of polymerization has been successfully implemented for radical polymerization, including for those monomers that show a pronounced gel-effect, and also for step-growth polymerizations. In both cases confinement effects have been incorporated into the models in order to describe the experimental data. Indeed, polymer nanostructures can be readily fabricated from monomers in a faster and less-energetic process than those obtained by polymer infiltration process. In particular, (i) the long polymer infiltration time (hours or days) can be overcome by the in situ polymer synthesis in 1-2 h; (ii) the high temperatures required for polymer infiltration (near 200 \({}^{\circ}\)C) and concomitant polymer degradation effect can be avoided since polymerization temperature is around 50-80 \({}^{\circ}\)C in most cases; (iii) thermoset polymers that cannot be infiltrated in AAO templates monomers (polymer does not melt) can be synthesized directly from the monomers in the AAO templates (most of monomers are liquid). Therefore, polymerization within AAO nanopores can be considered a complementary method to that of the infiltration of pre-formed polymers (nanomoduding) to obtain tailored polymer nanostructures.