Polyoxyethylene chain conformation

Ethoxylated nonionics show the lowest interfacial tension as well as high solubilisation and detergency around their cloud points [36, 54]. Sterically, their polyoxyethylene chains can assume two different conformations in aqueous solution at the low ethoxylation is has a fully extended trans or "zig-zag" form and at higher ethoxylation it has a more compact gauche or "meander" form. In the second case the saturation adsorption is not so high but the steric stabilisation of dispersions may be quite effective [7, 8]. 

A polyoxyethylene chain may exist in a large number of conformations, which have different energies. The conformation of an oxyethylene group, which is gauchegig) around the C-C bond and anti (a) around... 

Fujita and coworkers [79] smdied fluorescently labeled polyoxyethylene chains and found a good correlation between the concentration dependence of the friction coefficient evaluated from the anisotropy measurements and from the macroscopic viscosity. Fujita developed the fi ee-volume theory which describes reasonably well the concentration dependence of in the whole concentration region, [80] but it does not enable prediction of the parameters at a molecular level. Hyde et al. [81] used the Fujita theory for fairly successful interpretation of the experimental data. An interesting paper has been published by Viovy and Moimerie [82]. The authors studied concentrated solutions of anthracene-labeled polystyrene in toluene. They found good correlation of the local dynamics with the viscosity in the range of high concentrations and made one very important observation the local dynamics are unaffected by the overlap of the polymer chains that occurs at concentrations higher than c (concentration of the first overlap—see chapter Conformational and Dynamic Behavior of Polymer and Polyelectrolyte Chains in Dilute Solutions ). 

The degree of stability of many dispersions cannot be explained solely on the basis of Fa and Fr. Elworthy and Florence [56] have treated the stability of emulsions of chlorobenzene and anisole stabilized with a series of synthetic polyoxyethylene ethers in the light of colloid theory and have shown that electrical stabilization alone cannot explain the stability observed. The nature of this other force which is invoked to explain discrepancies between theory and experiment is not fully worked out. Nevertheless, much interest has been shown in this alternative mechanism of stabilization, which for non-ionic emulsions appears to play the major role [64]. Results have indicated that the thickness and degree of solvation of adsorbed layers is critical [65]. Thus, the particular conformation and length of the polyoxyethylene chains of non-ionic surfactants at interfaces is likely to be an important factor in the stabilization of emulsified droplets. 

ID and 2D 13C NMR were carried out in a series of novel nematogens by Bayle and co-workers to study the effects on the conformation and order due to the addition of lateral and/or terminal substituents.249 251 For example, lateral flexible substituents are found to adopt a mean conformation more or less parallel to the mesogenic core. As a result, lateral chains are less disordered than terminal chains. Nematogens containing polyoxyethylene ether (POE) chain as a lateral crown ether and terminal chain(s) have been... 

Macromolecules exist in a variety of conformational forms that range from randomly coiled chains to more spatially ordered structures. Of particular interest are the polymers that adopt helical symmetry. Helical conformation is a result of an orderly repeated unit with internal rotational angles along the polymer backbone. In the crystalline state, polyoxyethylene exists in a helical conformation that contains seven chemical units (-CH2CH2-O-) and two turns in a backbone identity period of 19.3 A (7-9). 

Isotropic correlation times and spin lattice relaxation times measured by and H-NMR for polyoxyethylene (POE) solutions in a variety of solvents have been computed using the DRIS formalism for isolated polymer chains [8]. For this purpose, the conformational kinetics of POE has been analyzed and kinetic schemes of rotameric transitions have been estimated for the three distinct types of bond pairs (CO, OC), (OC, CC) and (CC, CO) on the backbone. The effective friction coefficient is deduced from the viscosity of the solvent, irrespective of the size of the kinetic unit, assuming environmental effects and chain connectivity constraints to be of secondary importance compared to torsional energy barriers. The reader is referred to [8] for explicit expressions of... 

The serial product in equation (6) imphes that the Uj need not all be identical. The only restriction on their relationship is that all pairs must be conformable for matrix multiplication. Conformabihty is ensured by the requirements expressed in the first two points before equation (4). Equation (6) can be used with chains in which different types of bonds are present, as in polyoxyethylene (14). It can also be used for chains in which not all bonds have the same number of rotational isomeric states, as in the polycarbonate of bisphenol A (15). 

This behaviour is not very surprising as the cation has been used successfully in the synthesis of a series of crown ethers [111]. The template role of barium(II) is predominantly conformational. By coordination of the polyoxyethylene-containing ligson to barium(II) the terminal aldehyde groups are held in close proximity. Under such circumstances the cyclisation of the 1 4-1 open-chain condensation product occurring inevitably at the next step of the template process, is favoured over intermolecular pathways leading to polymerisation. The assembly of the above binucleating products in the absence of a template yields only small... 

Although most investigations of the effect of the length of the hydrocarbon chain on surface activity have been concerned with ionic surfactants, it is also clear from the available data from studies involving polyoxyethylene non-ionic surfactants that these too conform to Traube s rule [4]. 

ABSTRACT. The concept of "crankshaft-like motion" in the backbones of chain molecules implies much slower conformational transitions than in small molecules if two energy barriers have to be surmounted simultaneously. Studies of the rates of hindered rotation around the amide bonds in solutions of piperazine polyamides by NMR and of the photochemical and dark isomerization of polyamides with azobenzene residues in the chain backbone revealed no difference between these rates in the polymers and their analogs. Polyoxyethylene with a dibenzylacetamide residue in the middle of the chain exhibited similar excimer emission as N,N -di(p-methylbenzyl)acetamide. These observations imply that only one energy barrier is surmounted in conformational transitions of polymer backbones. 

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