Porogens assemble

Another possible way of overcoming the limitations posed by the presence of water in the suspension polymerisation process is to substitute the continuous water phase with alternative solvents that could still act as dispersing medium for the monomer mixture but better preserve noncovalent interactions in the template-monomer assembly. For example, liquid fluorocarbons are chemically inert and do not affect interactions which are used in noncovalent imprinting. Use of such solvents for the preparation of MIP microbeads has been demonstrated already in 1996 by Mayes and Mosbach [16,17]. A range of MIPs were prepared using Boc-l-phenylalanin as the template, MAA as the functional monomer and different kinds and amounts of crosslinkers and porogenic solvents. The resulting MIP microbeads... 

In the noncovalent approach, the monomer is self-assembled around the tern-plating molecule and then again copolymerized with the additional monomer. The template is then removed by using a porogenic solvent. 

Conventionally, MlPs are obtained by bulk co-polymerization from a mixture consisting of a functional monomer, cross-linker, chiral template, and a porogenic solvent mixture. Nowadays, imprinting via non-covalent template binding is preferred over the covalent mode and involves three major steps (see Fig. 9.9). (i) Functional monomers (e.g. methacrylic acid, MAA) and a cross-linker (e.g. ethyleneglycol dimethacrylate, EDMA) assemble around the enantiomeric print molecule, e.g. (S)-phenylalanine anilide (1), driven by non-covalent intermolecular interactions, e.g. ionic interactions, hydrogen bonding, dipole-dipole interaction. Tr-rt-interaction. (ii) By thermally or photochemi-... 

These templates can also be combined with other porogens (such as self-assembled polymers) or techniques to obtain hierarchical pore systems or structured materials on a number of length scales. Examples demonstrating the extension of simple templating to more complex structural control will also be given. 

Scott, E. A., M. D. Nichols, et al. (2010). Modular scaffolds assembled around living cells using poly(ethylene glycol) microspheres with macroporation via a non-cytotoxic porogen. Acta Biomaterialia 6(1) 29-38. 

A major limitation of this technique, however, is that the cross-linked PDMS stamps tend to swell in many organic solvents that include chloroform, methylene chloride, toluene, and tetrahydrofuran. These solvents have been widely used as porogens in the synthesis of molecularly imprinted polymers. The PDMS stamps swelled dramatically in these solvents and subsequently lifted off from the substrate [55]. Once a stamp has lost the conformal contact with the substrate, the assembly can no longer be used to make polymer structures. 

Design and fabrication of multidimensional nanostructures have been discussed for metals and ceramics in the previous chapters and most of the fabrication methods introduced earlier can be transferred to polymeric and composite systems. Generally, polymeric and composite nanostructures of different dimensions from 0-D (e.g., nanoparticles, nanodots) to 3-D (nanoscaffolds) can be fabricated by nanopattem-ing techniques, colloidal processes, electrospinning, physical and chemical vapor depositions, porogen strategy, self-assembly, and so on. These fabrication techniques discussed in the previous chapters are transferrable for preparing nanopolymers and... 

The nonhydrolytic M—O—M bond formation via ester elimination between metal alkoxides and carboxylic acids is a well-known approach in sol-gel chemistry. In this direction, titanium -butoxide and acetic acid were used for the nonhydrolytic synthesis of anatase Ti02 nanopartides at 100 °C [92]. Moreover, spindle-shaped nanoporous anatase Ti02 mesocrystals with a single-crystal-like structure and tunable sizes were synthesized in the tetrabutyl titanate and acetic acid system without any additives imder solvothermal conditions [93]. A complex mesoscale assembly process, involving oriented aggregation of tiny anatase nanocrystals and entrapment of in situ produced butyl acetate as a porogen, was proposed for the formation of the mesocrystals. They exhibited a good performance as anode material for lithium ion batteries [93]. 

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