Molecular electronics, dendritic polymer

Broadening the scope, we may briefly consider a nonexhaustive panorama of various types and features of supramolecular polymers depending on their constitution, characterized by three main parameters the nature of the core/framework of the monomers, the type of noncovalent interaction(s), and the eventual incorporation of functional subunits. The interactions may involve complementary arrays of hydrogen-bonding sites, electrostatic forces, electronic donor-acceptor interactions, metalion coordination, etc. The polyassociated structure itself may be of main-chain, side-chain, or branched, dendritic type, depending on the number and disposition of the interaction subunits. The central question is that of the size and the polydispersity of the polymeric supramolecular species formed. Of course their size is expected to increase with concentration and the polydispersity depends on the stability constants for successive associations. The dependence of the molecular weight distribution on these parameters may be simulated by a mathematical model [19]. These features are detailed in Chapters 2, 3, and 6 for various growth mechanisms. 

When homopolymers are crystallized from very dilute solutions, either lozenge-shaped platelets or crystals that possess a dendritic habit are formed. Some typical electron micrographs of the crystals precipitated from dilute solution are shown in Figs. 1.12 and 1.13. The crystal habit that is observed depends on the molecular weight of the polymer and the crystallization conditions, such as the temperature and the nature of the solvent. A very striking feature is that the platelets are only about 100 to 200 A thick. In conjunction with selected-area electron diffraction studies, it is shown that the chains are again preferentially oriented normal, or nearly so, to the basal plane of the platelet. Considering the... 

Jen a al. have developed dendronized polymeric NEO materials that have shown significantly improved poling efficiency by encapsulating chromophore with dendritic substituents that can electronically shield the core, ii-electrons, and form spherical molecular shapes." "" " Figure 6 illustrates different molecular architectures of dendronized side-chain NLO polymers with crosslinkers. The diverse selections of molecular architectures provide additional flexibility in the molecular engineering of high-performance polymeric NLO materials. Moreover, the unique nanoscale environment created by the shape and size, dielectric properties, and distribution of chromophores in crosslinkable polymers with dendrons and dendrimers can all play critical roles in maximizing the macroscopic EO properties of polymeric NEO materials. 

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