Synthesis of polyurethanes

Sucrose acrylate derivatives can be converted into polymers and hydrogels that can be used as flocculants, water adsorbents, bioimplantables, and dmg dehvery devices (42). Sucrose ethers have appHcations as surfactants and surface coatings, and as feedstocks for synthesis of polyurethane foams and... 

Hie most representative member of this class of polyesters is the low-molar-mass (M 1000-3000) hydroxy-terminated aliphatic poly(2,2/-oxydiethylene adipate) obtained by esterification between adipic acid and diethylene glycol. This oligomer is used as a macromonomer in the synthesis of polyurethane elastomers and flexible foams by reaction with diisocyanates (see Chapter 5). Hydroxy-terminated poly(f -caprolactonc) and copolyesters of various diols or polyols and diacids, such as o-phthalic acid or hydroxy acids, broaden the range of properties and applications of polyester polyols. 

Example 2. Two-Shot Cast Elastomer (Prepolymer Method). Synthesis of polyurethane elastomers via the prepolymer method is challenging and requires especial attention to details and techniques. This example is a relatively easy one, using a low-viscosity, 9.6% NCO MDI-based poly(tetramethylene ether) glycol prepolymer. It is adapted from the Bayer Product Information Bulletin for Baytec ME-090 prepolymer. 

Diol-functionalized telechelic polymers have been desired for the synthesis of polyurethanes however, utilizing alcohol-functionalized a-olefins degrades both 14 and 23. Consequently, in order for alcohols to be useful in metathesis depolymerization, the functionality must be protected and the oxygen atom must not be /3 to the olefin or only cyclic species will be formed. Protection is accomplished using a/-butyldimcthylsiloxy group, and once protected, successful depolymerization to telechelics occurs readily. 

This system was slightly modified by R J. Flory, who placed the emphasis on the mechanisms of the polymerisation reactions. He reclassified polymerisations as step reactions or chain reactions corresponding approximately to condensation or addition in Carother s scheme, but not completely. A notable exception occurs with the synthesis of polyurethanes, which are formed by reaction of isocyanates with hydroxy compounds and follow step kinetics, but without the elimination of a small molecule from the respective units (Reaction 1.3). 

DMAP has been found to improve the coupling reaction in solid phase peptide synthesis (4). Polypeptides synthesized via the DMAP-DCC method were found to be of higher purity compared to other methods of synthesis. In polymer chemistry, DMAP has been used for hardening of resins and in the synthesis of polyurethanes, (5) polycarbonates, (6) and polyphenyleneoxides (7) ... 

Synthesis of Polyurethanes. In the "prepolymer method" employed in this study, MDI (2 equivalents) and PPG (1 equivalent) were reacted at 60°C in the presence of 1% dibutyltin dilaureate as catalyst, in the melt. The course of the polymerizations was followed spectroscopically by observing the intensity of the — NCO peak in the IR (Scheme III). 

This section describes the synthesis of oxazolidine esters used as polymer hardeners that cannot be synthesized using chemical catalysis, the synthesis of polyurethane polymers with methods that avoid the use of isocyanates and the enzymatic synthesis of polyesters with low molecular weight dispersity. 

There have been many attempts to develop non-phosgenation routes to synthesize diisocyanates and for the synthesis of polyurethanes without the use of isocyanates. None of these has been applied commercially. In the conventional process, the addition of the... 

Another approach was attempted by Seppala and Kylma who reported the synthesis of poly(ester-urethane)s by condensation of hydroxyl terminated tel-echelic poly(CL-co-LA) oligomers with 1,6-hexamethylene diisocyanate (Scheme 33) [94]. The diisocyanate acts as chain extender producing an increase in molecular weight of the preformed oligomers. The authors claim that some of the copolymers present elastomeric properties. Using a similar method. Storey described the synthesis of polyurethane networks based on D,L-LA, GA, eCL,... 

Completely aliphatic polyesters, made from aliphatic diacid and aliphatic diol components), are not of major industrial importance because of their low melting temperatures and poor hydrolytic stability. (Low-molecular-weight aliphatic polyesters are used as plasticizers and prepolymer reactants in the synthesis of polyurethanes see Secs. 2-12e, 2-13c-2). 

The synthesis of polyurethanes is usually presented as proceeding via the formation of carbamate (urethane) linkages by the reaction of isocyanates and alcohols ... 

The synthesis of polyurethanes from tetramethylene urea, 1,2-propylene carbonate, and ethylene carbonate shows an interesting alternative route to polyurethanes 26 and 27 (Figure 11). The tetramethylene urea ring is not opened to form an isocyanate under the reaction conditions applied <2004MAC888>. 

Modern technological practice, particularly the various types of chemical processing, use a great variety of formulations for the synthesis of polyurethanes. Therefore it is nearly impossible to create a general kinetic model which would be valid for various polymerizing systems. However, the same general approach to creating such models can be used for different cases. Therefore, it is useful to demonstrate the method used to construct a model and its characteristic kinetic equations for some typical cases. 

The most comprehensive kinetic model for the synthesis of polyurethanes was developed by Macosko and his team.44"46 In all cases the heart of the model is the degree of conversion, p, which is defined for polyurethane synthesis as... 

Scheme 6.8. Synthesis of polyurethanes based on the thermal decomposition of a blocked fervisocyanate monomer.

Another example of the step-growth polymerization is the synthesis of polyurethanes. Here, linear polyurethanes are produced by the reaction of bifunctional alcohols, HO — R — OH, with bifunctional isocyanates, OCN — R — NCO, to produce a polyurethane (see Figure 3.21). 

There are very important investigations into the synthesis of polyurethanes done by Malichenko et al. [75]. These authors carried out the synthesis of numerous diisocyanates ... 

Step-growth polymerization, 22, 24-25, 23, 84-86, 86,90-92,114-115, 261 compared with chain-growth polymerization, 88-89, 88-89 interfacial polymerization, 91-92 laboratory activities on synthesis of nylon, 228-230 synthesis of polyesters in the melt, 231-233 synthesis of polyurethane foam, 234-237 molar mass and, 86, 86 polycondensation of poly ethylene terephthalate), 90-91 polymers produced by, 86 types of monomers for, 90 Stereochemistry, 28, 37-39,41-42, 70 tacticity, 103-105 Stereoisomers, 41 Stereoregularity, 70 Stiffness, 142, 261 Strain, 142-143, 261 Strength... 

Otto Bayer discovers the polyaddition synthesis of polyurethanes and proves that some form of cross linking is necessary for reversible elasticity... 

Some step-growth polymerizations involve reactions where no small molecules (like HCI or HjO) are split out at all, as in the synthesis of polyurethanes, shown schematically in Figure 3-14. Isocyanates are... 

The hydroxyl number is very important for the synthesis of polyurethane. It is defined as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the sample. The principle of the analytical method is that the hydroxyl group is esterified with a solution of phthalic anhydride in pyridine. The excess reagent is back-titrated with standard sodium hydroxide solution, and a blank is run on the reagents to determine the amount of anhydride consumed. The phenolphthalein is an indicator for the titrate. Because the color of recycled polyol is dark brown, the faint pink endpoint is not clear, so a potentiometric titrate can be applied. 

Phosgene is very commonly employed in polymerisation reactions. Its role in the synthesis of polyurethanes and of polycarbonates has been described in Chapter 4, and reactions in which polymers are modified by post-treatment with COCl have been described in Chapter 10 (under the Section most appropriate to the type of functional group involved). This Section is mainly concerned with the reactions of phosgene to give novel polymers. 

From their previous experience in the synthesis of polyurethanes for dialysis membranes, Lyman and Associates(5.) also introduced a segmented polyether polyurethane which has shown excellent thromboresistance. (A)... 

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