Template-assisted polymerization

Template-assisted polymerization of condueting polymers has been an effective way to reproducibly fabricate conducting-polymer nanowires. Fundamentally, the technique employs a hard membrane template with pores of uniform length and diameter, typically composed of alumina. Polymerization can be performed chemically using a mixture of... 

Most of the template techniques for the achievement of nanostmctured macromolecules are described more extensively in the sub-chapters 3 Grafting polymerization and 4 Electrochemical methods . Hereafter, some examples of polymeric materials obtained in nano-size dimension through the use of different template-assisted polymerization methods will be shown. 

Figure 11.24 Molecularly imprinted polymers (MIP) random (top) and template-assisted (bottom) polymerization process.

The template-assisted synthetic strategies outlined above produce micro- or mesoporous stmetures in which amorphous or crystalline polymers can form around the organic template ligands (174). Another approach is the use of restricted spaces (eg, pores of membranes, cavities in zeolites, etc.) which direct the formation of functional nanomaterials within thek cavities, resulting in the production of ultrasmaU particles (or dots) and one-dimensional stmetures (or wkes) (178). For example, in the case of polypyrrole and poly(3-methylthiophene), a solution of monomer is separated from a ferric salt polymerization agent by a Nucleopore membrane (linear cylindrical pores with diameter as small as 30 nm) (179—181). Nascent polymer chains adsorb on the pore walls, yielding a thin polymer film which thickens with time to eventually yield a completely filled pore. De-encapsulation by dissolving the membrane in yields wkes wherein the polymer chains in the narrowest fibrils are preferentially oriented parallel to the cjlinder axes of the fibrils. 

Fig. 5 Models of prion replication, (a) The template assistance model predicts that a PrPSo monomer is more stable than PrPc, but is kinetically inaccessible. In the rare event that a PrPSo monomer is created spontaneously (or provided exogenously), it can template the misfolding of another PrPc molecule by direct interaction. The dashed line shows that the newly created PrPSc monomer can act as another seed to formation of PrPSc. (b) The nucleation polymerization model predicts that barrier to prion protein conversion is the formation of a nucleus in which the protein adopts a PrPSo-like structure. The formation of such a low order aggregate is not favored however, once it has formed, polymerization from a pool of PrPc molecules can take place efficiently. Fragmentation of the polymer increases the number of ends for the recruitment of PrPc monomers...

Figure 8.1 Two different pathways for aniline enzymatic polymerization. On top, traditional ortho-coupling. Below, template-assisted enzymatic polymerization of aniline. (Reproduced with permission from [15]. Copyright (1998) American Chemical Society).

Self-doped PANI are very interesting due to their unique electrochemical behavior unlike PANI, the self-doped polymer remains in its doped state in near neutral or alkaline media [28]. Fully self-doped PANIs are not easy to synthesize due to the lower reactivity of acid-functionalized anilines. Kim et al. [29, 30] introduced an alternative approach in the template-assisted enzymatic polymerization of aniline. Previously, only polyanionic templates had been used for PANI synthesis. However, acid-functionalized anilines bear a net anionic charge in aqueous solution, and attempts to use SPS as template with carboxyl-functionalized aniline resulted in red-brown colored polymers with no polaron transitions, regardless of the synthetic conditions. The use of polycationic templates, such as those shown in Figure 8.2 allowed the synthesis of linear and electrically conductive PANIs with self-doping ability due to the doping effect of the carboxyl groups present in the polymer backbone. 

However, to draw a final conclusion as to whether the presented synthesis route can deliver economically viable polymeric materials for templated-assisted manufacturing of nanomaterials, the following question has to be experimentally clarified Can the involved ATRP and ROP be scaled up to yield larger batches of double-gyroid-forming material of at least 1-100 kg This would however require reduction of the amount of copper catalyst for the ATRP to the ppm range. One kilogram of polymeric material would be sufficient to coat an area of 100 m with a 10 xm thick template film. 

Sudha, J.D. and Sivakala, S. (2009) Conducting polystyrene/polyaniline blend through template-assisted emulsion polymerization Colloid Polym. Sci.. 2X7,1347-1354. 

Wire-shaped growth of nanostructured PPy with diameter <10 nm, has been obtained by electropolymerization at naturally occurring step defects and artificially formed pit defects of HOPG, in a template assisted electropolymerization where the size of the nanostmctures could be controlled by limiting the pyrrole polymerization time at anodic potentials [242], Electrochemical polymerization of pyrrole within the confines of anodized alumina templates and subsequent metal nanoparticles immobilization on the surface of polymer pillars has been used to make surfaces that show roughness on two independently controllable levels sub-microscopic roughness from polymer pillar dimensions and nanoscopic roughness from the appropriate size selection of metal NPs [243],... 

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