Diol polyethers

Owing to their improved stability towards hydrolysis and oxidation, dimer diol polyethers (and dimer diol polycarbonates) are used as soft segments in the preparation of thermoplastic polyurethanes. Polyurethanes prepared from such oleo-chemical building blocks are very hydrophobic and show the expected stability. 

As an alternative to polyester diols, polyethers (such as polypropylene glycol) that are even more flexible are often used. These are bonded to smaller (150-nm) rigid domains from the (aromatic) isocyanate. The chain extender in the formulation may be either flexible or rigid. 

The polyether diols derived from polyesters seem to represent a compromise between cost and their contribution to superior elongation and tensile properties as compared to plain polyether diols polyether diols from polyester account for about 10% of the flexible PUR production. Examples of useful products formed from hydroxy-terminated esters of terephthalic acid (TPA)— formed, in turn, by the reaction of an excess of glycols with dimethyl terephthalate (DMT) or TPA—and TDI or MDI-PMDI are flexible ski clothing, gaskets, rollers for printing presses, etc. [85],... 

Segmented polyurethanes were synthesized from the a, to diol polyethers listed in Table I and the diisocyanates IV, V, and VI by the two-step process shown in Figure 1 or the three-step process in Figure 2. In all cases, chain extension of isocyanate-terminated prepolymers was accomplished with ethylenediamine. The synthesis took place in a 2 1 (v/v) mixture of dimethyl sulfoxide and 4-methyl-2-pentanone at 60°C. 

Gel permeation chromatography (GPC) (Waters Model 244, with micro Styragel columns) of the diol polyethers and of the prepolymers created therefrom, in combination with data from the literature, confirms that these idealized types must be modified by the following considerations ... 

Most of the a, co diol polyethers had the most probable distribution of molecular weight (1). Thus, weight-to-number average is around two, and the lengths of polyether chains between diisocyanate groups vary correspondingly. 

Highest-ranking acid, polyester with diol Cyclic ether, poly ether Diol, polyether... 

Diol, polyether with bivalent radical See also Polyacetal... 

Polymers of the first group are typified by the poly(alkylene terephthalate)-poly[poly(oxy-alkylene) terephthalate] family which are conveniently prepared by the copolyesterification of dimethyl terephthalate with mixtures of a short-chain diol and a poly(oxyalkylene)-a,(o-diol according to the general scheme of equation (3).7,8,9o,i68-i75 M ny different diols, polyether diols and aromatic dicarboxylate esters other than terephthalates have been employed in such itivesti-gations, " " and a generalized view of the properties attainable is shown in Figure 3. 

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

Some of the simplest polyols are produced from reaction of propylene oxide and propylene glycol and glycerol initiators. Polyether diols and polyether triols are produced, respectively (27) (see Glycols). 

Titanium-containing polyethers have been prepared by the reaction of dicyclopentadienyltitanium dichloride with aromatic and ahphatic diols via an interfacial and/or aqueous solution polycondensation technique (273). 

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stabiHty (22). The hydrolytic stabiHty of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

Polyester and polyether diols are used with MDI in the manufacture of thermoplastic polyurethane elastomers (TPU). The polyester diols are obtained from adipic acid and diols, such as ethylene glycol, 1,4-butanediol, or 1,6-hexanediol. The preferred molecular weights are 1,000 to 2,000, and low acid numbers are essential to ensure optimal hydrolytic stabihty. Also, caprolactone-derived diols and polycarbonate diols are used. Polyether diols are... 

The secondary hydroxyl groups of these poly(oxypropylene) glycol diols are less reactive than the primary hydroxyl groups of the earlier polyesters. At the time of the introduction of these polyethers, the catalysts then available were insufficiently powerful for one-shot processes to be practical and so these polymers have been used primarily in prepolymer processes. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The polyols used are of three types polyether, polyester, and polybutadiene. The polyether diols range from 400 to about 10,000 g/mol. The most common polyethers are based on ethylene oxide, propylene oxide, and tetrahydrofuran or their copolymers. The ether link provides low temperature flexibility and low viscosity. Ethylene oxide is the most hydrophilic and thus can increase the rate of ingress of water and consequently the cure rate. However, it will crystallize slowly above about 600 g/mol. Propylene oxide is hydrophobic due to hindered access to the ether link, but still provides high permeability to small molecules like water. Tetrahydrofuran is between these two in hydrophobicity, but somewhat more expensive. Propylene oxide based diols are the most common. 

Polyester diols are often combined with polyether diols to provide green strength through crystallization or elevated r . Most prevalent and least expensive is hexamethylene diol adipate (HDA) with a Tm of about 60°C. A variety of polyesters are available with various levels of crystallinity — from wax-like to amorphous — and crystallization rate, and with values ranging well below 0°C to above room temperature. Polybutadiene diols are the most expensive and most hydrophobic. They provide low surface tension and thus good wet out of non-polar surfaces. 

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