Molecular weight polyether triols

A similar structure to the one in Figure 6.6 is obtained by using instead of epoxy resins diphenylmethane diisocyanate (MDI pure or crude ). For example by using crude MDI with the functionality of around 2.2-2.5 -NCO groups/mol, by the reaction with terminal groups of high molecular weight polyether triols (5000-6500 daltons), nonreactive NAD... 

This kind of NAD, resulting from the reaction of crude or pure MDI with high molecular weight polyether triols, is very efficient in stabilising copoly (ACN - styrene) dispersions or even polystyrene dispersions in polyether polyols. 

Flexible foams are based on polyoxypropylenediols of 2000 molecular weight and triols up to 4000 molecular weight. Rigid foams are based on polyethers made from sorbitol, methyl glucoside, or sucrose. 

The high reactivity of the isocyanate moiety has been exploited to yield polyurethane/urea hydrogels. A polyisocyanate prepolymer obtained by fiinctiontdizing a moderate molecular weight polyether diol or triol with a diisocyanate will crosslink on exposure to an aqueous environment due to partial hydrolysis and urea formation (55). A similar hydrogel results by reacting a polyisocyanate... 

Polyethers prepared from propylene oxide are soluble in most organic solvents. The products with the highest hydroxyl number (lowest molecular weight) are soluble in water, not in nonpolar solvents such as hexane. The solubihty of 3000 molecular weight triols is high enough in solvents such as toluene, hexane, and methylene chloride that the triols can be purified by a solvent extraction process. 

This reaction is truly tempting because it potentially satisfies the need in the search for a way to reclaim the chemical value of a polyurethane recycle foam project [12, 13]. When a polyurethane foam is hydrolyzed, it gives aromatic diamine and polyether polyol, both in very crude forms. The diamine can be purified by regular means, but the crude polyether polyol cannot be easily cleaned up due to its polymeric nature. If this Ganem reaction can work well, the polyether polyol stream can be converted to a low-molecular-weight chemical, which can then be purified by conventional process such as distillation. Indeed, when this reaction was tried on a polyether triol of 3000 molecular weight as a model, the diacetate of propylene glycol was isolated by distillation. Unfortunately, the yield was too low to be of practical interest. 

We observed in a previous investigation of PU s derived from a kraft lignin (KL)-polyether triol-diphenylmetane diisocyanate (MDI) system (Yoshida, H. Morck, R. Kringstad, K. P. Hatakeyama, H., submitted to J. Appl Polym. Set.) that KL fractions of low molecular weight yielded more flexible and less crosslinked PU s than the medium and high molecular weight KL fractions. This was attributed to the lower functionality of the low molecular weight KL fractions. 

Yoshida H, Morck R, Kringstad KP, Hatakeyama H (1990) Kraft lignin in polyurethanes. II. Effects of the molecular weight of kraft lignin on the properties of polyurethanes from a kraft lignin-polyether triol-polymeric MDI system. J Appl Sci 40 1819-1932... 

IPDI-based prepolymer. This is an aliphatic prepolymer formed by the reaction of IPDI with polyether polyol (3000 molecular weight PPO-based triol) (PPG = polypropylene oxide). The NCO group content of such systems is about 3.4%, and the viscosity about 15 000 CP at 20°C. Solid content is typically 98%-100%. The general reaction is given in Figure 2.22. This prepolymer may typically be used in two-part elastomer systems. 

An ingeniously simple screening method was used by Britain and Gemeinhardt [146] to evaluate catalysts for the isocyanate/hydroxyl reaction. To approximate as closely as possible actual polymerization conditions, the 80 20 ratio of 2,4- and 2,6-tolylene diisocyanate (80 20 TDI) isomers and a polyether triol of 3000 molecular weight were mixed at NCO OH ratio of 1.0. A 10% solution of catalyst in dry dioxane was added, the final catalyst concentration being 1% of the weight of polyether. The time for the mixture to gel at 70°C was noted as an indication of catalytic strength. This technique used the same reactants employed in one-shot flexible polyether-based foam systems, almost completely eliminated solvent, and was used to screen quickly hundreds of possible catalysts. 

The catalyst makes it possible to product outstandingly high-equivalent-weight polyether polyols, e.g., about 10,000. In other words, polyether diols of 20,000 molecular weight and polyether triols of 30,000 molecular weight can be produced. 

Figure 27. Relationship between Aliphaticity Index and equivalent ratio at different molecular weights of polyether triol (65).

The one-shot methods used to produce flexible polyurethane foams employ quick mixing of a (usually) triol-based polyether of fairly high-molecular weight with toluene diisocyanate, catalyst, and water for gas production (Eq. 21.19). The reaction of water with the diisocyanate rapidly raises the average functionality in the polymerizing system by forming urea, as well as urethane links (Eq. 21.23). 

The preferred polyether used in this reaction is a higher molecular weight triol of 5000-6000 daltons (preferred MW is 6000 daltons). By copolymerisation of the macromer (structure 6.12) with ACN and styrene, a NAD is obtained in situ, which is in fact a graft copolymer ... 

Reaction 11.4 is used to decrease the unsaturation of polyether polyols simultaneously with the functionality increase. Thus, by introducing a polyether polyol with high unsaturation (0.07-0.09 mequiv/g), a low molecular weight polysiloxane compound, having 2-3 Si-H groups/mol, together with a platinum catalyst, the polyether monol present in the polyether (in fact allyl ether based polyethers) is added to the polysiloxane compound and the monol is transformed into a diol or into a triol (reaction 11.5). 

The polyether polyols for rigid PU foams based on polyols which are liquid under the conditions of alkylene oxides polymerisation are glycerol and TMP polyether triols, of various molecular weights, sorbitol-based polyols (based on a mixture of sorbitol - glycerol, sorbitol - dipropyleneglycol, sorbitol - dithylene glycol) and xylitol-based polyether pentaols. 

These "polymer-polyols" are made by the in situ polymerization of vinyl monomers such as acrylonitrile (although grafting with other monomers has also been reported in a liquid polyol solution, e.g., polyether triol of molecular weight 3000) to give stable dispersions of the polymeric portion in the liquid polyol. Grafting is carried out with azobis(isobutyronitrile) or dibenzoyl peroxide as initiators at 80-90 °C. A polymer-polyol containing about 20% acrylonitrile appeared to be the best compromise between polyol viscosity and urethane foam properties (108). 

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