Polyethylene supramolecular structures

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. 

The present article is centered around macromolecular and supramolecular structures obtained upon use of benzene as a regular building block. While, e.g., the gas permeability of polyethylene tereph-thalate)s,35 the mechanical strength of carbon fibers,36 and the ion conductivity of polybenzimidazoles24 are important features from a practical viewpoint, the focus here is on the occurrence of -conjugation, or lack thereof, originating from the repetition of the aromatic benzene units in various structural motifs. If the reader regards materials... 

Lee et al. showed that control of the supramolecular structure in rod—coil molecular systems containing either polyethylene oxide) (8) or polypropylene oxide) (17) coils and induction of ordered structures... 

Interesting supramolecular structures can furthermore be obtained by the controlled crystallization of polymers hke polyethylene or nylon-6,6 on carbon nanotubes. The latter serve both as template and as nucleus of crystallization. There are in principle three modes of how a polymer crystal might grow on a nanotube surface (a) Phase separation may occur in the course of the crystallization so the initially dispersed carbon nanotubes rea omerate and precipitate, (b) The polymer coils around the individual tubes whose solubility increases in the sequel,... 

The mechanical loading on a polymeric item not only changes its shape and sizes but also affect substantially its supramolecular structure. The mechanical loading on the amorphous-crystalline polymer (polyolefins) substantially influences first of all on the amorphous phase of the polymer. The stretching strain results in the conformational transitions the number of gauche conformations decreases and the number of trans conformations increases (polyethylene, poly(ethylene terephthalate)). Under strain chains of macromolecules are additionally oriented and the rotation of the rad-... 

For polymer chemists it is interesting to know how well-known linear polymers can be linked with dendritic architectures and what the supramolecular consequences of this approach might be. Combination of dendrimers with linear polymers in hybrid linear-dendritic block copolymers has been employed to achieve particular self-assembly effects. Block copolymers with a linear polyethylene oxide block and dendritic polybenzylether block form large micellar structures in solution that depend on the size (i.e., the generation) of the dendritic block [10]. Amphiphilic block copolymers have been prepared by the combination of a linear, apolar polystyrene chain with a polar, hydrophilic poly(propylene imine) dendrimer [11] as well as PEO with Boc-substituted poly-a, -L-lysine dendrimers, respectively [12]. Such block copolymers form large spherical and cylindrical micelles in solution and have been described as superamphi-philes and hydra-amphiphiles , respectively. 

Rogers, R.D. Bauer, C.B. Structural Chemistry of Metal-Crown Ether and Polyethylene Glycol Complexes Excluding Groups 1 and 2. In Comprehensive Supramolecular Chemistry, Atwood, J.L., Davies, J.E.D., MacNicol, D.D., Vogtle, R, Eds. Elsevier Science Oxford, UK, 1996 Vol. 1, 315-355. 

---