Ethers terminal chains

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... 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

Transfer and termination occur by the modes described previously for cyclic ether polymerizations. Chain transfer to polymer (both inter- and intramolecular) is facilitated in cyclic acetal polymerizations compared to cyclic ethers because acetal oxygens in the polymer chain are more basic than the corresponding ether oxygens [Penczek and Kubisa, 1989a,b]. Working at high monomer concentrations, especially bulk polymerizations, is used to depress cyclic oligomer formation. 

The general design concept for liquid crystalline crown ethers discussed in this section consists of a rigid core with terminal chains and a laterally attached crown ether unit (Fig. 3). 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

Continuing their investigations, Percec and coworkers also considered several generations of benzyl ether monodendrons containing only one ahphatic terminal chain on the outside benzyl groups (Fig. 5) [ 113]. Optical polarizing... 

The deformulation of a polyester was done with liquid-adsorption chromatography under critical conditions (LACCC) that was coupled to an SEC system. The dimension was separated by the end-group functionality to study byproducts formed during polycondensation. By 2D chromatography a number of species (e.g., cycles, ethers, alkyl terminated chains, and so on) could be identified. Some of them influenced the mechanical and thermal properties of the polyesters significantly. 

One of these, which has recently become increasingly important in electrochemical applications, and which is one of the materials discussed extensively in this volume, is the Nafion ionomer family. These materials were developed by the duPont company, and consist of hydrophobic fluorocarbon backbone chains, with hydrophilic per-fluorinated ether side chains terminated by sulfonic acid groups or corresponding alkali salts. The Nafions possess many exceptional properties which are not encountered in other ionomer systems, particularly the high water permeability (26,27), permselectivity with regard to ion transport (28-30), durability in strong alkali (26), thermal stability (26,31), and others. 

While a munber of alternative polymer membranes have been developed. Nation is still considered the benchmark of proton conducting polymer membranes, and has the largest body of research hterature devoted to its study. Alternative polymer membranes are almost invariably compared to Nation . Nation is a free radical initiated copolymer consisting of crystaUiz-able, hydrophobic tetrafluoroethylene and a perfluorinated vinyl ether terminated by perfluorosulfonic acid. Nation 117 possesses an equivalent weight of 1100 (EW = mass of dry ionized polymer (g) in the protonic acid form that would neutralize one equivalent of base). Thus, there are 13 perfluoro-methylene groups (-CF2-) ( = 6.5) between pendent ionic side chains. 

Many molecules exhibiting liquid crystal properties have either a terminal alkyl or alkyl ether group. The terminal chains exhibit a number of different conformations, as in (31) ... 

Separation by the end-groups functionality (cycles, ether, alkyl terminated chains). Two-dimensional characterization. Addition of hexane supports adsorption. 

---