Monomer preorganization

The imprinting process shown schematically in Fig. 21 involves the preorganization of functional monomer molecules such as methacrylic acid and... 

Nevertheless, the RNA World hypothesis would seem to answer most of the questions raised above how can an essentially linear molecule be autocatalytic, how can it synthesize proteins, and how can it replicate Autocatalysis can occur because RNA can adopt a wide range of secondary and tertiary structures that position RNA monomers into a preorganized sequence and link them together, it can apply the same flexibility to bind other small molecules and catalyse their polymerization, and it could form weakly interacting sense and antisense duplexes. The main problem is... 

Ultimate progress in the control of the primary structure of synthetic macromolecules might be expected if it were possible to develop a template type synthesis, in analogy to the polymerase chain reaction [27]. In spite of many efforts, no successful concept has yet been developed, which is no surprise regarding the complicated supramolecular interactions involved in the necessary steps, i.e. preorganization of the template, binding of the monomer, initiation and termination of the polymerization, and the release of the formed raacromolecule from the template [28,29]. 

It has been attempted to perform template polymer syntheses without using biological sources. Concepts focus on the formation of a complex between monomer molecules and a present macromolecule [4,480], This way the monomer will get preorganized and the polymerization is supposed to follow a zip mechanism controlled by the length and the configuration of the template polymer, offering replication of the molecular weight and control of the stereo structure. Polymerization of acrylic acid in the presence of poly(ethyleneimine), N-vinylimidazole/ poly(methacrylic acid) or acrylonitrile with poly(vinylacetate) have been described [469,470,471,472,473]. Recently the preparation of solid polyelectrolyte complexes from chitosan and sodium-styrenesulfonate has been reported [481]. 

Hydrophobic Interactions for the Preorganization of Functional Monomers and Template in Water... 

In contrast with hydrogen bonding, hydrophobic interactions work in aqueous solutions. By choosing appropriate functional monomers, we can utilize these interactions for the preorganization in water. Cyclo-... 

The Uquid-soUd interface is an ideal environment to carry out reactions. In a first example, we highhght the preorganization of monomers as a prerequisite for reactivity on a surface 2D crystal engineering in aid of chemical reactions. In a second example, the adsorbed molecular species catalyze an industrially relevant reaction and with the help of STM, important aspects of this reaction are revealed in real time and space. 

The synthetic routes used to prepare main-chain poly(2]catenanes are summarized in Scheme 17.3. Most often, they are prepared via the polymerization of difunctional [2]catenane monomers, such that the preparation of difimc-tional [2]catenane monomers represents the key step. In route 1, cychzation of a preorganized precursor affords the difunctional [2]catenane monomer, while in route 2 the difunctional (2]catenane monomer is synthesized directly via a template-directed cychzation reaction of two hemicyclic precursors. In route 3, stepwise threading and cyclization reactions are employed to prepare difunctional [2]catenane monomers. In route 4, urdike routes 1 to 3, covalent bonds are used as templating units during the second cyclization reactions to prepare difunctional [2]catenane monomers. Route 5 illustrates the preparation of difunctional bis[2]catenane monomers whereby, when difunctional [2]catenane or bis[2]catenane monomers are in hand, the main-chain poly[2]catenanes can be prepared via polymerization of the difunctional catenane monomers. 

It should be stressed at this point that, even if monomers could be preorganized into a 2-D assembly with a positional order, many hurdles must stiU be overcome when converting this assembly into a 2-D polymer. The countless options for... 

The polydiacetylenes and polytriacetylenes differ from polyacetylene because preorganization of the diacetylene and triacetylene is required for a successful polymerization (7). This remarkable observation was first recognized (8,9) in 1969 and marks the beginning of modern polydiacetylene and polytriacetylene chemistry. In a few cases, this topochemically controlled polymerization occurs from a crystal of the monomer to a crystal of the polymer, giving rare examples of macroscopic single polymer crystals (9). 

Preparation of Polydiacetylene. The preorganization for the 1,4-polymerization of diacetylenes has been discussed previously (7,14,15). Successful polymerization occurs when the diacetylenes have a translational repeat distance (d) of about 0.49 nm and an angle (tt) of about 45° with respect to the translational direction and van der Waals contact (i v) of the polydiacetylene functionalities (Fig. 1). If these structural parameters are met then the Cl and C4 carbon atoms of adjacent diacetylenes will be in a position for a topochemically controlled polymerization. Because the 0.49 nm translational repeat distance (d) of the monomer is about the same as the repeat distance in the polymer, the pol5nnerization process can occur with little disruption of the reactant packing. 

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