Urethanes synthesis

However, identifying the general category of backbone element is not the only thing that should be classified. We should be able to estimate the average molecular weight, or, really better, the NCO to OH ratio used in the urethane synthesis, the overall ... 

In the presence of sodium ethoxide in ethanol, the urethane synthesis starting from 4-amino-l-benzyl-i,2,5,6-tetrahydropyridine-3-carbonitrile and diethyl carbonate affords as a byproduct 6-benzyl-4-ethoxy-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-2(lA/)-one (6).496... 

Fomrez . [Witco/Organics] Foam crosslinkers, i ecursors for reactive diluents, chain extenders in urethane synthesis, coupling agent catalyst flexible cellular PU foam for textile and industrial applies., dispersing agents, coatings, aefeesives, elastomers. 

Szelest-Lewandowska, A., Masiulanis, B., Szymonowicz, M. et al. (2007) Modified polycarbonate urethane synthesis, properties and biological investigation in vitro. Journal ofBiomedical Materials Research, Part A, 82A(2), 509-520. 

The e-f-fect o-f organic additives on the activity o-f a selenium catalyst in phenyl urethane synthesis by the carbonyl at i on o-f PhH02 has been studied (30. ... 

Hiltunen K., Seppala J.V., Harkonen M., Lactic acid based poly (ester-urethanes) Use of hydroxyl terminated prepolymer in urethane synthesis, J. Appl. Polym. ScL, 63, 1997, 1091-1100. 

Many of the commercial reactants used in urethane synthesis are impure materials, for example MDI may be used as pure MDI, a low melting-point (38°C) solid polymeric or crude MDI, which is a dark-coloured low viscosity liquid. Alternatively, MDI and TDI prepolymers may be blended and perhaps have various additives incorporated, all of which may affect the final quantity of free NCO available for reaction. Also, active isocyanate content of a prepolymer decreases with storage, a decrease of about 0-05% per month being normal. For these reasons it is necessary to measure and specify the amount of isocyanate available for reaction at any specific time, and this is done by calculation of the isocyanate equivalent weight of the mixture using the following procedure ... 

He M, Chu C. A new family of functional biodegradable arginine-based polyester urea urethanes synthesis, chracterization and biodegradation. Polymer 2013 54(16) 4112-25. 

The bis(4-diphenylmethaneurethanes), Urethane-n, were either synthesized by a separate method starting from 4-hydro-xybutyIdiphenylmethane-4-carbamate or similar to POTM-n-Urethane synthesis by reacting the Diol-n with 4-diphenylme-thaneisocyanate. 

HydrophobicaHy Modified, Ethoxylated Urethane. HEUR associative thickeners are in effect poly(oxyethylene) polymers that contain terminal hydrophobe units (66). They can be synthesized via esterification with monoacids, tosylation reactions, or direct reaction with monoisocyanates. There are problems associated with aH of the methods of synthesis. The general commercial procedure for their synthesis is by a step-growth addition of... 

Glycols such as neopentyl glycol, 2,2,4-trimethyl-l,3-pentaiiediol, 1,4-cyclohexanedimethanol, and hydroxypivalyl hydroxypivalate are used in the synthesis of polyesters (qv) and urethane foams (see Foamed plastics). Their physical properties are shown in Table 1 (1 6). 

Several modified forms of this synthesis are available. For example, treatment of either isocyanate (28) or urethane (29) derivatives with phosphoryl chloride followed by stannic chloride has been reported to give the substituted isoquinoline [80388-01-8] (158). 

Practical methods for synthesis and elucidation of the optimum physical forms were developed at Du Pont (13). The violets fill the void in the color gamut when the inorganics are inadequate. The quinacridones may be used in most resins except polymers such as nylon-6,6, polystyrene, and ABS. They are stable up to 275°C and show excellent weatherabiUty. One use is to shade phthalocyanines to match Indanthrone Blue. In carpeting, the quinacridones are recommended for polypropylene, acrylonitrile, polyester, and nylon-6 filaments. Predispersions in plastici2ers ate used in thermoset polyesters, urethanes, and epoxy resins (14). 

The basis of most one-component, moisture-curing urethanes is the synthesis of an isocyanate-terminated prepolymer, as shown ... 

Catalysts serve a dual purpose in one-component moisture-curing urethanes. The first purpose is to accelerate the prepolymer synthesis. The second purpose is to catalyze the curing reaction of the adhesive with moisture. The most common catalysts used to promote both prepolymer formation (NCO/OH) and later the adhesive curing reaction (NCO/H2O) are dibutyltin dilaurate and DMDEE ((tertiary amine. A stabilizer such as 2,5-pentanedione is sometimes added when tin is used, but this specific stabilizer has fallen from favor in recent years, due to toxicity concerns. DMDEE is commonly used in many one-component moisture-curing urethanes. DMDEE is one of the few tertiary amines with a low alkalinity and a low vapor pressure. The latter... 

The waterborne prepolymer process is similar to the prepolymer synthesis described earlier, except that most of the waterborne prepolymers are based on aliphatic isocyanates and contain an internal emulsifier. There are several types of internal emulsifiers, both anionic and cationic. A good summary of these stabilizers is found elsewhere [56], The majority of the waterborne urethanes are anionic dispersions. An internal surfactant, such as dimethylolpropionic acid, is often incorporated into the prepolymer ... 

The chain extension step may then take place in the water phase. Hydrazine and ethylene diamine are commonly used chain extenders for waterborne urethane dispersions. The isocyanates react with the diamine chain extenders much faster than with the water, thus forming polyurea linkages and building a high molecular weight polymer. More detailed information regarding the synthesis and process of making waterborne polyurethane dispersions is found in Dieterich s review article [58]. 

The similarity between the cryptands and the first of these molecules is obvious. Compound 7 7 is a urethane equivalent of [2.2.2]-cryptand. The synthesis of 7 7 was accomplished using a diacyl halide and l,10-diaza-18-crown-6 (shown in Eq. 8.13). Since amidic nitrogen inverts less rapidly than a tertiary amine nitrogen, Vogtle and his coworkers who prepared 7 7, analyzed the proton and carbon magnetic resonance spectra to discern differences in conformational preferences. Compound 7 7 was found to form a lithium perchlorate complex. 

A related enamine alkylation is seen in the rearrangement of an ethylene imine vinylogous amide, which was heated with sodium iodide in diglyme. The presumed internal enamine alkylation constitutes a critical step in an oxocrinane synthesis (265). Use of an ethylene imine urethane for alkylation of an enamine and formation of the hexahydroindole system has also been reported (266). 

Works on the oxidation of uric acid has unequivocally established the triazine structure > ° (9) of oxonic acid. This is further confirmed by the straightforward synthesis described by Piskala and Gut. ° The reaction of biuret (11) with potassium ethyloxalate yielded a potassium salt (24), that with ethyl oxamate, the amide of oxonic acid (25). Both these compounds were converted to 5-azauracil. An analogous reaction with diethyloxalate which should produce an ester of oxonic acid resulted in a mixture of urethane and parabanic acid, however. 

Thyagarajan and Majumdar (Ref 18) have studied the condensations of urethanes with formaldehyde under various exptl conditions and accomplished the selective synthesis of either six-membered 1,3,5-triazines or eight-membered 1,3,5,7-tetrazocines. These are nonnitrated analogs of RDX and HMX respectively. Their results are summarized in Fig 4... 

Scheme 7 Cyclopentene ring closure in the presence of urethane and sulfonamido groups in total synthesis of agelastatin (38) [30]...

Polyols and polyamines are the most important coreactants for isocyanates. As briefly outlined in Section 4.2.2, the two most common classes of urethane-grade polyols are the polyethers and polyesters. In this section their synthesis and structure are discussed. Other polyol types, such as acrylic resins and polycarbonates, are of more limited applicability and are not presented here. 

Synthesis of hydrolytically stable siloxane-urethanes by the melt reaction of organo-hydroxy terminated siloxane oligomers with various diisocyanates have been reported i97,i98) -yhg polymers obtained by this route are reported to be soluble in cresol and displayed rubber-like properties. However the molecular weights obtained were not very high. A later report56) described the use of hydroxybutyl terminated disiloxanes in the synthesis of poly(urethane-siloxanes). No data on the characterization of the copolymers have been given. However, from our independent kinetic and synthetic studies on the same system 199), unfortunately, it is clear that these types of materials do not result in well defined multiphase copolymers. The use of low molecular weight hydroxypropyl-terminated siloxanes in the synthesis of siloxane-urethane type structures has also been reported 198). 

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