Polymer backbone structure

The affinity of the polymer-bound catalyst for water and for organic solvent also depends upon the structure of the polymer backbone. Polystyrene is nonpolar and attracts good organic solvents, but without ionic, polyether, or other polar sites, it is completely inactive for catalysis of nucleophilic reactions. The polar sites are necessary to attract reactive anions. If the polymer is hydrophilic, as a dextran, its surface must be made less polar by functionalization with lipophilic groups to permit catalytic activity for most nucleophilic displacement reactions. The % RS and the chemical nature of the polymer backbone affect the hydrophilic/lipophilic balance. The polymer must be able to attract both the reactive anion and the organic substrate into its matrix to catalyze reactions between the two mutually insoluble species. Most polymer-supported phase transfer catalysts are used under conditions where both intrinsic reactivity and intraparticle diffusion affect the observed rates of reaction. The structural variables in the catalyst which control the hydrophilic/lipophilic balance affect both activity and diffusion, and it is often not possible to distinguish clearly between these rate limiting phenomena by variation of active site structure, polymer backbone structure, or % RS. 

Fig. 8 Polymer backbone structures of SCLCPs based on cyanobiphenyl mesogens...

Table 6.1 Some polymer backbone structures forming the basis for conducting materials ...

Synthesis of highly crowded graft copolymers with graft frequencies of up to 50% of the total monomeric units in approximately alternate positions on the polymer backbone (structure 24). 

Molecular structure, chain flexibility, and molecular weight determine the DR effectiveness of high polymers. Polymer backbone structure and side groups as well as solvent-polymer interactions determine the flexibility of the molecule [Patterson et al., 1969] as well as the polymer electrostatic charge in aqueous systems. 

Table 1 Surface energies for characteristic polymer backbone structures...

The transport-active groups can be part of the polymer backbone structure, they can be covalently linked as pendant groups to a vinyl or similar chain such as carbazole groups (substituted aromatic amines) in PVK, or need not be covalently attached to the polymer backbone at all. Indeed, solid solutions of NIPC in polycarbonate display hole mobilities that are comparable to those in PVK [19, 20]. The polymer backbone in PVK does not contribute to transport, but merely ties the transport-active groups together. Similarly, both solid solutions of triphenylamine (TPA) in polycarbonate [21] and poly (methacrylate) with pendant triphenylamine groups [22] display photoconductivity and charge transport. 

An assumed potential energy function must both force a collection of atoms to assume a realistic polymer backbone structure, and create reasonable conformational dynamics. We have performed simulations wherein the bonds are kept at a distance of about 1.53A by a potential quadratic in the separation between successive bonds. Similarly, a quadratic potential keeps the bond angles near the tetrahedral value. Each bond experiences a rotational potential as shown in Figure 6. Several other features of the true potential are omitted as not contributing qualitatively to the mechanics. Substituent groups are considered as collapsed onto the carbon centers of the backbone. Excluded volume forces between remote carbons are omitted, as are hydrodynamic interactions. 

Optically active polymers containing carbazole groups may be synthesised by polymerisation of intrinsically optically active carhazole-containing monomers or by copolymerisation of a variety of optically active co-monomers with nonchiral carbazole-containing monomers. Full details are given and it is concluded that the second method is most useful, not least because it permits a wider variation in polymer backbone structures. V. V. absorption fluorescence emission, NMR, and circular dickroism spectra are reported in detail and help to establish a correlation between photophysical behaviour widi both primary and secondary structural features of the polymers. 

Polysulfone (PSU) is a family of thermoplastic polymers they are classified as PSU, poly(aryl sulfone), and poly(ether sulfone) (PES) by the polymer backbone structure. They are well known for their toughness and stability at high temperatures (-100°C to 150°C), high oxidative stability, and dimensional stability. Hence, it is easy to get the thin membrane with reproducible properties, which have been widely used in many fields like hemodialysis, wastewater treatment, gas separation, and especially PEM fuel cell applications. 

Others also prepared AEMs through similar three-step procedures based on lab-synthesized PSUs in the literatures. The polymer backbone structures were not identical to commercial PSUs by changing the diphenol comonomers. Also, various amination reagents besides common trimethylamine were used, such as 1,1,2,3,4-pentamethylguanidine (PMG), DABCO, and morpholine. ... 

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