Polyethers general structures

For those familiar with polymer chemistry, polyurethane may be a confusing term. Unlike polyethylene, the polymerization product of ethylene, a polyurethane is not the result of the polymerization of urethane. To add to the confusion, a urethane is a specific chemical bond that comprises a very small percentage of the bonds of a polyurethane. Since we are interested in chemical and physical effects, polyether or polyester is a more descriptive term for the most common bond in a polyurethane. Despite this complication, it is instructive to begin by talking about the methane bond from which the polyurethane name is derived. The general structure or bond that forms the basis of this chemistry is the urethane linkage shown in Figure 2.1. 

We have previously synthesized a number of titanium polyethers of the following general structure (3,4). A variety of aromatic and aliphatic diols were successfully incorporated as the fundamental backbone units of the polyethers. These materials are insoluble and do not soften prior to thermal-induced degradation. 

Today the bulk of the polyether polyols used for flexible foams are propylene oxide polymers. The polymers prepared by polymerizing the oxide in the presence of propylene glycol as an initiator and a caustic catalyst are diols having the general structure... 

The first commercial thermoplastic elastomers (TPE) were the thermoplastic urethanes (TPU). Their general structure is A-B-A-B, where A represents a hard crystalline block derived by chain extension of a diisocyanate with a glycol. The soft block is represented by B and can be derived from either a polyester or a polyether. Figure 5.1 shows typical TPU structures, both polyester and polyether types. 

Not taking cyclic molecules into account, the general structures of industrial silicone surfactants for flexible slabstock foam production can be seen in Figure 2.13. The main building blocks of these materials are a PDMS backbone and attached polyethers based on ethylene oxide and propylene oxide addition products. The siloxane backbones can either be linear or branched and can have their polyether substituents attached in an either pendant or terminal location. These four general structures are outlined in Figure 2.13). 

Several groups of polymers were tested. The initial group consists of a series of organotin polyethers synthesized as part of our overall anti-cancer effort. Table 17.3 [85,86]. They have the following general structures (Structure 17.10). 

Polyether carboxylates have been evaluated as biodegradable detergent polymers, initially by Crutchfield [150] and later by Procter Gamble [151], and Matsumura et al. [152]. All these polymers fit the general structure of the series... 

Polyethers n. A polymer of general structure [R-0] , where R may be a simple alkene group. 

FIG. 7 General structure for polyether siloxanes (polydimethylsiloxane-polyoxyal-kylene copolymers). 

The nonionic derivatives are primarily represented by the polyether-polydimethyl-siloxane copolymers. The general structure of these surfactants is illustrated below. The hydrophilic chain(s) generally contain EO/PO block copolymers. When several hydrophilic chains are distributed on the polymer backbone, the resulting molecular structure is similar to a comb therefore, such molecules are often called comb-like surfactants. 

Polyether ether ketone, hard plasticizer-firee polymer with the general structure (with x= 2, y=l) ... 

These techniques can be extended to more complex systems. Kozlowska and Slonecki [21] prepared polyether-6-polyamide-6-polyesters by polycondensing a dimerized fatty acid M = 570), an a,u -diamino-polyether, dimethyl-terephthalate, and butane-l,4-diol. The soft segments consisted of the polyether and the fatty acid moiety. Their general structure is given in Scheme 17. 

Polyoxometalates also play an important role in the selection of a metal ion for its complete encapsulation in the cavity of a crown ether to form an unusual supramolecular cation structure. For example, the crown ethers (macrocyclic polyethers), generally, do not readily form complexes with first-row transition metals in their low oxidation states because such metal ions provide only soft coordination (acceptor) sites and crown ethers have hard donor atoms. Naturally, only a few first-row transition metal rown ether complexes had been structurally characterized in which a direct bond formation between a transition metal and the crown ether oxygen atoms became possible rare examples of this kind are offered by the smaller ring crown ethers (e.g., 15-crown-5 and... 

Macrocyclic polyethers containing the 2.2-paracyclophane unit are interesting structures and several such compounds have been prepared . Despite the diverse structural possibilities, the syntheses of these molecules have generally been accomplished by straightforward Williamson ether syntheses. The only unusual aspect of the syntheses appears to be a novel approach to certain paracyclophanes developed by Helgeson (see footnote 7a in Ref. 91). The first step of Eq. (3.28) illustrates the formation of the required tetrol, which is then treated with base (KOH or KO-t-Bu) and the appropriate diol dito-sylate to afford the macrocycle. 

The general molecular structure of polyether-based polyurethanes is illustrated in Fig. 25.3 a). Typical polyether sequences include polyethylene glycol and polypropylene glycol. The length of the polyether sequences between urethane links can vary from one or two ether groups up to several hundred. As the length of the polyether sequences between urethane links increases, the polymer exhibits more of the properties normally associated with polyethers. 

Polyether-based foams account for more than 90% of all flexible polyurethane foams. The properties of foams are controlled by the molecular structure of the precursors and the reaction conditions. In general, density decreases as the amount of water increases, which increases the evolution of carbon dioxide. However, the level of water that can be used is limited by the highly exothermic nature of its reaction with isocyanate, which carries with it the risk of self-ignition of the foamed product. If very low density foams are desired, additional blowing agents, such as butane, are incorporated within the mixing head. 

Typical systems. A considerable number of immobilized polyether systems have been synthesized both for phase transfer catalysis as just discussed and for use in a number of analytical applications. Such immobilized systems are generally synthesized by either copolymerization of suitably functionalized macrocycles in the presence of cross-linking agents or by appending functionalized macrocycles to existing polymeric substrates. Structures (184)-(186) give examples of different... 

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