Supramolecular polymer structures

Among other subjects the influence of the conditions, in which the polymerization process is conducted, on the supramolecular structure of the polymer formed is discussed in studies40-42. Using these data the researchers analyzed the impact of polymerization kinetics on the polymers supramolecular structure and formulated the basic principles for controlling the structure of the polymer in the course of its synthesis. They also proposed a new thermodynamic approach for controlling supramolecular structures. The possible uses of this method are demonstrated in the polymerization of trioxane and triethylamine in different solvents and at different monomer concentrations. The purpose of this approach and the manner in which it differs from the conventional kinetic approach are roughly illustrated by the scheme in Fig. 5. 

Several polymer supramolecular structures such as dendrimeric structures (Fig. 11.1), polymersomes, PICsomes, and layer-by-layer (LbL) capsules (Fig. 11.4) have been used to provide defined reaction spaces, where catalytically active molecules can perform their activity [19,25,56,71]. Such polymer 3D supramolecular assemblies are generated by various methods (1) specific synthesis (dendrimers), (2) self-assembly (polymersomes and PICsomes), and (3) adsorption of polymer layers on colloidal templates (LbL capsules) [25,37,56,71],... 

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

Fig. 21 a-c. Schematic representation supramolecular structure of a crystalline rigid-chain polymer (a), an idealized ECC of a flexible-chain polymer (b) and an orientationally crystallized sample with a spatial ECC framework (c)... 

Given the actual scenario, one can state that the emerging field of nanotechnology represents new effort to exploit new materials as well as new technologies in the development of efficient and low-cost solar cells. In fact, the technological capabilities to manipulate matter under controlled conditions in order to assemble complex supramolecular structures within the range of 100 nm could lead to innovative devices (nano-devices) based on unconventional photovoltaic materials, namely, conducting polymers, fuUerenes, biopolymers (photosensitive proteins), and related composites. 

Due to its unique chemical composition and structure, DNA can interact with a plethora of chemical structures via numerous types of bonds. This property ultimately defines the ability of DNA fragments to serve as the building blocks in the complex three-dimensional self-assembled structures. Following we Ust four major types of polymer/DNA interactions that can lead to formation of supramolecular structures ... 

It hag been shown that transition of a backbone carbon from the sp to sp state is promoted by tensile stresses and inhibited by compressive strains (10,44). The acceleration of the process of ozone oxidation of the polymers under load is not associated with the changes in supramolecular structure or segmental mobility of the chain. The probably reason of this effect is a decreasing of the activation energy for hydrogen abstraction (44). The mechanism of initial stages of the reaction of ozone with PP can be represented as ... 

In some of these type of polymeric materials there are two forces that organize the polymer strands into a supramolecular structure, and are usually hydrogen bonds and 7r-7r interactions, this happens with the complex [l,2,4,5-C6H2 CH20CH2C(pz)3 4Ag2(BF4)2] .605... 

As illustrated in the diagram below, domain swapping can also result in indefinite polymerization to form linear supramolecular structures. These may correspond to present-day polymers of proteins such as microtubules, or they may represent abnormal structures, like the straight and paired-helical filaments in the neurofibrillary tangles observed in the brain tissue of those afflicted with Alzheimer s disease. 

Finally, Chap. 6 deals with the exploitation of biocatalysis in generating supramolecular polymers, a class of polymers where the monomers are connected via non-covalent bonds. This approach provides highly dynamic and reversible supramolecular structures, inspired by biological polymeric systems found in the intra- and extracellular space. A number of potential applications of enzymatic supramoleular polymerizations are discussed in the context of biomedicine and nanotechnology. 

As discussed in Section 3.1.6.1., natural biopolymers are useful chiral selectors, some of which are readily available they are constructed from chiral subunits (monomers), for instance, from L-amino acids or D-glucose. If synthetic chiral polymers of similar type are to be synthesized, appropriate chiral starting materials and subunits, respectively, must be found. Chiral polymers with, for example, a helical structure as the chiral element, are built using a chiral catalyst as chirality inducing agent in the polymerization step. If the chirality is based on a chiral subunit, the chirality of the polymer is inherent, whereas if the polymer is constructed from chiral starting materials, chiral subunits are formed which lead to chirally substituted synthetic polymers that in addition may order or fold themselves to a supramolecular structure (cf. polysaccharides). 

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

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