Chain structures perfect linearity

Fig. 37 Linear chain formation of DNA-coated paramagnetic polystyrene colloids with the different self-protection schemes displayed in Fig. 33. By using an external magnetic field, DNA-functionalized particles were brought together into linear chains, after which the temperature was lowered below the association temperature for beads, and the field turned off. (a) Representative microscopy picture of the resulting chain structures immediately after switching off the magnetic field, (b-d) Chains after 1 h at the specified temperature for particles functionalized with sticky end sequences able to form both loops and hairpins (b, c) or only loops (d). The degree of aggregation of chains in (d) is intermediate between the unprotected, branched chains in (b) and the perfectly linear, protected chains in (c). Adapted with permission from [157]...

The X-ray analysis indicated a zig-zag chain in the solid state with an Sn-O-Si bond angle of 156 ° and perfectly linear Si-O-Si linkage. Interestingly, the polymeric solid-state structure transforms to the six-membered cyclic structure in solution. Equation (3.8.10). 

Experimental results on reactions forming tri- and tetrafunctional polyurethane and trifunctional polyester networks are discussed with particular consideration of intramolecular reaction and its effect on shear modulus of the networks formed at complete reaction. The amount of pre-gel intramolecular reaction is shown to be significant for non-linear polymerisations, even for reactions in bulk. Gel-points are delayed by an amount which depends on the dilution of a reaction system and the functionalities and chain structures of the reactants. Shear moduli are generally markedly lower than those expected for the perfect networks corresponding to the various reaction systems, and are shown empirically to be closely related to amounts of pre-gel intramolecular reaction. Deviations from Gaussian stress-strain behaviour are reported which relate to the low molar-mass of chains between junction points. 

In your mind you might envision a polymer as an indefinitely long, linear chain. In reality, this is rarely the case. Whether by design or by accident, most polymers deviate from perfect linearity, and these deviations profoundly affect a polymer s properties. Here we review some of the basic issues in polymer topology (recall from Chapter 6 that for most structures the topology of a molecule is established solely by its connectivity). 

With a coordination number 2, no true layer structure but at best a layered chain structure is possible. In other words, macroscopically, such a crystal can well possess one perfect cleavage plane, though the bonding is linear. 

In polytetrafluoroethylene, the energy of C-F bond is very high (485 kJ/mol) and is responsible for perfectly linear chains. This structural property is due to... 

An alternative view of the polysilane structure is depicted using the worm-like model as proposed for poly(diacetylene)s59, where the linear chain has a large number of small twists without sharp twists playing a special role60-62. In this model, a Gaussian distribution of site energies and/or exchange interactions and the coherence of the excitation is terminated by any of the numerous usual random deviations from perfect symmetry. 

Macrotnolecules are formed by covalent bonding of a large number of monomeric units. This results in a wide variety of possible structural architectures, e.g. linear chains, branched chains, brush-like chains ( hairy rods ), star-like, tree-like ( hyperbranched ), perfectly branched ( dendritic ) structures (Figure 1) [14,15],... 

X-Ray analysis confirms the structure shown for the polymer, and the bond distances found for the chain indicate that B is the major contributing structure - . Intense bands for C=C and C=C in the Raman spectra also indicate that B is the major contributor, but the relatively low frequencies for these vibrations as well as the linear correlation found between the two frequencies for various polymers suggest that A makes a significant contribution . Both frequencies are found to increase with decreasing phase perfection. 

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