Polyether-urethane reactions

Two different polyurethanes were used as starting materials a solid elastomer based on a trifunctional polyethertriol, 1,4-butanediol and methylenebis(phenyl isocyanate) and a flexible foam where the diol was replaced by water. The ammonolysis reactions were carried out at 139 °C and 140 atm for 120 min, and with a polyurethane/ammonia weight ratio of 1. Under these conditions the polyurethane conversion was practically total. The ammonolysis reaction transforms the CO group into urea and the ester groups and derivatives of carboxylic acids into amides, whereas ether and hydroxy groups are inert towards ammonia. Scheme 2.7 illustrates the stoichiometry proposed by the authors for the ammonolysis of the polyether urethane. 

Two-Package Polyol Urethane Coatings (ASTM Type 5). Two-package polyol urethane coatings consist of isocyanate-terminated adducts of polymers that are cured by reaction with di- or polyfunctional hydroxyl-containing materials. The latter may consist of low- to medium-weight polyols with a polyester, polyether, polyether urethane, or castor oil backbone. When the two components (OH- and NC0-) are mixed together, they have only a limited pot life. Therefore, the components are mixed prior to application. Catalysts may be used to speed up the cure either for room temperature or oven cure. 

When the process involves two competitive reactions, some people prrfer to call those modified polymers interpenetrated polymer networks (IPNs) [5]. The formation of a polyether-urethane network in a loosely crosslinked poly(methyl methacrylate) matrix to increase its toughness can serve as one of the examples. From a general point of view, the analysis of the reaction-induced phase separation is the same (perhaps more complex) for IPNs than for rubber-modified epoxies or for high-impact polystyrene. 

Acid number is of concern with both polyether and polyester polyols, since acidity affects the kinetics of the urethane reaction. Determination is by po-tentiometric titration. 

For both polyethers and polyesters that are to be utilized for polyurethane formation the acid and hydroxyl content are of prime concern, as in formulating for polyurethane applications all active hydrogens that take part in the urethane reaction need to be known as accurately as possible. Unless these variables can be closely controlled, accurate NCO/OH ratios will not be possible and it will prove difficult to manufacture polyurethanes of consistent quality. 

The hydrolysis reaction is preferably carried out under alkaline conditions. Acid hydrolysis can lead to undesired side reactions and also incomplete reaction. Hydrolysis by water under pressure is also incomplete, especially in the case of aromatic polyurethanes. Alkaline hydrolysis in glass containers can give large amounts of silicate which interfere with subsequent analysis, and for this reason the use of steel or even nickel-coated steel containers is recommended. The hydrolysis of polyester urethanes yields the diamine from the diisocyanate, and the acid salt and glycols from the polyester. Hydrolysis of polyether urethanes yields the diamine and the polyether. If diamines are used as curatives then two diamines will be present in the hydrolysis products. 

Addition of one monomer at a later point of the reaction results in the formation of latex particles of the core-shell type [479]. For special lattices, acrylonitrile and methacrylic acid are added [480,481]. Heat-sensitive lattices contain such additives as quaternary ammonium compounds, sulfonamides, polyether urethanes, and organopolysiloxanes, which affect the coagulation of the latex above a certain temperature [482]. 

The Price Award patent covers elastomeric polyurethanes made from the reaction of diisocyanates with the propylene oxide adducts of polyols. These polyether urethanes have proved to be of great commercial value as foamed rubber products, which have contributed greatly to the comfort and well-being of mankind. Approximately 1 billion lbs of these superior foamed products are used each year in the United States, particularly in cushioning for furniture and cars. 

Urethane Polymers. An important use for glycerol is as the fundamental building block ia polyethers for urethane polymers (qv). In this use it is the initiator to which propylene oxide, alone or with ethylene oxide, is added to produce ttifunctional polymers which, on reaction with diisocyanates, produce flexible urethane foams. Glycerol-based polyethers (qv) have found some use, too, ia rigid urethane foams. 

Propylene oxide and other epoxides undergo homopolymerization to form polyethers. In industry the polymerization is started with multihinctional compounds to give a polyether stmcture having hydroxyl end groups. The hydroxyl end groups are utilized in a polyurethane forming reaction. This article is mainly concerned with propylene oxide (PO) and its various homopolymers that are used in the urethane industry. 

The first step in formulating a urethane sealant is to prepare what is commonly called the prepolymer, typically by reaction of a hydroxy-terrninated polyether with a stoichiometric amount of a diisocyanate. Each hydroxy group reacts with one end of every diisocyanate molecule. 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

This process is based on the very high reactivity of the isocyanate group toward hydrogen present ia hydroxyl groups, amines, water, etc, so that the chain extension reaction can proceed to 90% yield or better. Thus when a linear polymer is formed by chain extension of a polyester or polyether of molecular weight 1000—3000, the final polyurethane may have a molecular weight of 100,000 or higher (see Urethane polymers). 

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