Poly ether polyols structure

The superior characteristics of polyester polyol based polyurethanes are explained by a better crystalline structure [1, 7] in the urethane segment, compared to the majority of poly ether polyols which are amorphous [except polytetrahydrofuran (PTHF)], due to the superior secondary forces between the polyester chains [8] and also due to a superior thermal and fire resistance, compared to polyether polyol based polyurethanes. Polyester-based polyurethanes (flexible foams, coatings), have a superior solvent resistance compared to the polyether-based polyurethanes [8]. 

By solubilisation of propoxylated bisphenol A with the structure 15.28, in a sucrose-based polyether polyol for rigid foams, an homogeneous mixture is obtained [29]. The viscosities of these mixtures increase with the content of propoxylated bisphenol A. From these mixtures rigid PU foams were obtained. Due to the aromaticity introduced by the propoxylated bisphenol A, the physico-mechanical properties of the resulting rigid PU foams were superior to the rigid PU foams made with the sucrose-based poly ether polyol alone [29]. 

By hydrolysing a polyether PU, a polyether polyol is obtained with a similar structure to those of the initial virgin poly ether polyol. For polyester PU the hydrolysis reaction is more complicated because the esteric groups of polyesters are hydrolysed back to monomers, such as diacids and glycols or polyols (reaction 20.3). 

The aromatic nuclei of the bisphenol A segment have a high affinity for the aromatic nuclei of styrene - ACN copolymer styrene units, the polyether chains having a strong interaction with the liquid poly ether medium. As an immediate consequence, the structure 6.15 assures a good steric stabilisation of polymeric dispersions in liquid polyether polyols (see the structure in Figure 6.6). 

Poly(tetramethylene oxide) polyols (see Scheme 4.4) are a special class of polyethers syndiesized via acid-catalyzed ring-opening polymerization of tetrahy-drofuran. Although less susceptible to side reactions, the synthesis of these C4 ethers is less flexible in terms of product composition and structure. Thus, because of diis syndietic route, only two-functional glycols are available and copolymers are not readily available. Molecular weights of commercial C4 glycols range up to about 3000 g/m. 

The only large-scale application of sucrose ethers appears to be to use poly-(9-(hydroxylpropyl) ethers, generated by alkoxylation with propylene oxide, as the polyol component for rigid polyurethanes —sucrose itself gives only brittle ones—which are used primarily in cushioning applications. The structures of these products, that is, the positions at which sucrose is alkoxylated and then carbamoylated with diisocyanates, and the type(s) of cross-linking involved, are not well defined though. 

The addition of carbodiimides, e.g. Staboxal PCD, which is supplied by Bayer, to poly(ester-urethanes) is one of the most effective ways to stabilize them against hydrolysis. Also the polyurethane structure can be tailored for better hydrolysis resistance through elimination or reduction of the ester groups present in the polyol. Hydrolysis resistance increases in the order of ether > polycaprolactone > polyester. Satrastab, developed by SATRA (Shoe and Allied Trades Research Association, Kettering, England), is also claimed to be an effective hydrolysis stabilizer for formulated polyurethanes in poromeric footwear materials. 

Bis(arenediazonium) salts of general structure (12) are reported to crosslink poly(vinyl alcohol) by formation of ether linkages," as shown in equation (13), where the polyol is represented by POH. As in the case of bisazido compounds, crosslinking requires that both diazonium groups react, each with a different polymer. 

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