Polymer side group

In atactic polymers, side groups are irregularly positioned on either side of the chain, as illustrated schematically in Fig. 1.8 c). A truly atactic polymer would comprise a random distribution of steric centers. In practice, atactic polymers typically show some preference for either meso or racemic placement The tendency towards stereoregularity is due to the fact that polymerization catalysts often contain steric centers, which tend to direct the incoming monomers and the growing chain into preferred configurations. 

Scheme 15 Regioselective transesteiification of polymer side-group esters [108]...

Thus, the possibility to regulate effectively the orientation of polymer side groups by varying the parameters of the electric field, together with the possibility to fix the oriented structure in a glassy state enables the use of such LC systems for making polymeric materials with required optical properties. 

The semipermeability behavior of a polymer him can be measured by equipment that permits measurements of the diffusion of a small-molecule dye through the membrane. In the phosphazene systems investigated, the rate of diffusion varied with the polymer side group ratio. A typical polymer with roughly 50% of the side groups as methylamino and 50% as trifluoroethoxy showed a faster transmission of dye molecules in water than did standard cellulose dialysis tubing. 

Just one example will be given here.195 Evaporation of water from aqueous solutions of MEEP and the enzyme urease yields films that can be cross-linked by exposure to gamma rays. The cross-linked films absorb water to form hydrogels in which the enzyme molecules are trapped within the interstices of the gel network. Some of the enzyme molecules may also be covalently grafted to the polymer side groups. The immobilized enzyme retained approximately 80% of its activity for the conversion of urea to ammonia. This system can, in principle, be used for the immobilization of a wide variety of enzymes, and for their use in biochemical flow reactors, or in sensors. 

Although the interface models by the MD methods provide a picture of the atomic distribution of the interface, because of the limitation of the MD method, the details of the interface structure in the vicinity of the electrode is not accurate. The effect of polymer side groups and backbone on the interface structure, specifically the... 

An iso tactic polymer (side groups on the same side of the backbone)... 

Some reactions taking place during pyrolysis occur through an E, mechanism (see Section 2.1). These reactions are not slowed down by free radical inhibitors, and therefore they do not involve free radicals. Typical reactions of this type are eliminations of small molecules such as HX (X = F, Cl, Br), water, methanol, ammonia, CO, CO2, etc. from the polymer side groups, A typical example of elimination reaction can be represented schematically by the equation ... 

It is not well understood how torsional motion of a polymer side group is affected by the rest of the polymer chain in highly dilute solutions. In the case of intramolecular exciplex formation of l-(l-pyrenyl)-3-(4-N,N-dimethylaminophenyl) propane bonded to polystyrene [14], the rate of exciplex formation in dilute polymer solution is much slower than that of a reference small molecule system. 

As mentioned, the electric field induces the orientation of polymer side groups. The homeotropic structure with an alignment of these groups (Ae > 0) normal to the electro-optical cell areas is thus formed. The possibi>... 

Figure 1.13. Backbone patterns in a few inorganic polymers. Side groups can be organic or inorganic.

In an extensive work on polysiloxane polymer liquid crystals, Finkelmann et al. examined their performance in a twisted nematic electro-optical cell. In parallel with the polymer measurements, analogous studies were carried out on low molar mass nematic compounds of equivalent dielectric anisotropy (Ae). Both the low molar mass nematic materials and the polymer side-group moieties were mixtures of methoxy- (or alkyloxy-) and chlorine-terminated benzoate esters. Cells were prepared using rubbed polyimides and in the polymer case the samples were annealed for several hours to obtain defect-free aligned textures. Measurement of the threshold voltages, for both the low molar mass compounds and the polymer, showed ... 

Scherowsky G, Fichna U, Wolff D (1995) Ferroelectric liquid-crystalline polymers side-group derived from mesogenic vinyl ether monomers. Liq Cryst 19(5) 621-627. doi 10.1080/... 

Water-soluble pol3aners are of great industrial and commercial importance. While water-soluble organic polymers have been widely studied, their inorganic counterparts have been largely left unexplored. Modification of the polymer side groups at silicon has been shown to allow access to water-soluble PFSs. For... 

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