Monomers in polyurethane

We will return to these reactions later in connection with polyurethanes because one monomer in polyurethanes is toluene diisocyanate, and the first step in its synthesis is the production of dinitrotoluene. 

The direct oxidation of ethylene to EO by O2 has now replaced the chlorohydrin process entirely because it is cheaper and involves less byproducts, but propylene oxide (a monomer in polyurethanes) is still made by the chlorohydrin route. 

Phosgene is a key intermediate used in synthesis of many chemicals, a major one being toluene diisocyanate, a monomer in polyurethanes. Phosgene is made from chlorine and carbon monoxide through the overall reaction... 

Composites Formed by Interstitial Polymerization of Vinyl Monomers in Polyurethane Elastomers 1. Preparation and Mechanical Properties of Methyl Methacrylate Based Composites, Polymer 14(12), 597 (1973). Polyurethane/poly(methyl methacrylate) semi-SINs. Interstitial composites. Synthesis and properties. Morphology. A series of six papers by Allen and coworkers. Other papers are in Polymer 14, 605 (1973) 15, 13, 19, 28, 33 (1974). 

The hydroxyl groups can be esterified normally the interesting diacrylate monomer (80) and the biologicaky active haloacetates (81) have been prepared in this manner. Reactions with dibasic acids have given polymers capable of being cross-linked (82) or suitable for use as soft segments in polyurethanes (83). Polycarbamic esters are obtained by treatment with a diisocyanate (84) or via the bischloroformate (85). 

Uses. The largest uses of butanediol are internal consumption in manufacture of tetrahydrofuran and butyrolactone (145). The largest merchant uses are for poly(butylene terephthalate) resins (see Polyesters,thermoplastic) and in polyurethanes, both as a chain extender and as an ingredient in a hydroxyl-terminated polyester used as a macroglycol. Butanediol is also used as a solvent, as a monomer for vadous condensation polymers, and as an intermediate in the manufacture of other chemicals. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

Ttihaloacyl aromatics have been prepared by Friedel-Crafts acylation of aromatics with CX COCl (X = Cl, Br) in the presence of AlCl. They are used as monomers in the preparation of polycarbonates, polyesters, polyamides, polyketones, and polyurethanes (91). 

Only a few commercial uses for TDA per se have been found. In epoxy curing appHcations, 2,4- I DA has been used as a component of a eutectic mixture with short chain aUphatic glycidal ether resins (46) as well as by itself (46,47) TDA (46) and single isomers (47) are also used as amine curatives. TDA can be used as a chain extender in polyurethanes (48,49). TDA is cited as a monomer in making aromatic polymers with unique properties, eg, amorphous polyamides (50), powdered polyamides (51), and low melting, whoUy aromatic polyamides (52). 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

Rastogi, S. C., Analysis of diisocyanate monomers in chemical products containing polyurethanes by high pressure liquid chromatography, Chro-matographia, 28, 15, 1989. 

One alternative is to select precursors which form a gas as a reaction product in situ during the network formation of thermosets. However this approach is restricted to a very limited number of precursors reacting via a polycondensation mechanism to split off a gas. For example, flexible polyurethane foams are commercially produced using CO2 that is liberated as a reaction product of the isocyanate monomer with water [5]. Very recently, Macosko and coworkers studied the macroscopic cell opening mechanism in polyurethane foams and unraveled a microphase separation occurring in the cell walls. This leads to nanosized domains, which are considered as hard segments and responsible for a rise in modulus after the cell opening [6]. 

Table 8.9 shows the non-fuel uses of toluene. Some of the toluene goes into gasoline depending on its supply and price compared to other octane enhancers. Of the other uses of toluene about half is converted into benzene by hydrodealkylation, though this amount varies with the price difference between benzene and toluene. 2,4-Toluene diisocyanate (TDI) is a monomer for polyurethanes. Included in miscellaneous uses is 2,4,6-trinitrotoluene (TNT) as an explosive. 

Two other derivatives of toluene are the important explosive trinitrotoluene (TNT) and the polyurethane monomer toluene diisocyanate (TDI). TNT requires complete nitration of toluene. TDI is derived from a mixture of dinitrotoluenes (usually 80% o,p and 20% o,o) by reduction to the diamine and reaction with phosgene to the diisocyanate. TDI is made into flexible foam polyurethanes for cushioning in furniture (35%), transportation (25%), carpet underlay (20%), and bedding (10%). A small amount is used in polyurethane coatings, rigid foams, and elastomers. 

The extent of crosslinking in polyurethanes depends on a combination of the amount of polyfunctional monomers present and the extent of biuret, allophanate, and trimerization reactions [Dusek, 1987]. The latter reactions are controlled by the overall stoichiometry and the specific catalyst present. Stannous and other metal carboxylates as well as tertiary amines are catalysts for the various reactions. Proper choice of the specific catalyst result in differences in the relative amounts of each reaction. Temperature also affects the extents... 

Phosgene, an intermediate in polyurethane monomer, is made by the homogeneous reaction... 

Toluene diisocyanate is commonly produced as a mixture of the 2,4- and 2,6-iso-niers, that is used as a monomer in the preparation of polyurethane foams, elastomers and coatings, as a cross-linking agent for nylon-6, and as a hardener in polyurethane adhesives and finishes. Polyurethane elastomers made from toluene diisocyanates are used in coated fabrics and clay-pipe seals. Polyurethane coatings made from toluene diisocyanates are used in floor finishes, wood finishes and sealers, and in coatings for aircraft, tank trucks, truck trailers and truck fleets (United States National Library of Medicine, 1997). 

Polymerizing acrylic monomers in the presence of oil-modified polyurethane leads also to a grafting onto the polyacrylics, resulting in dispersions suitable for stable water-borne latexes with good adhesion properties and fair hardness properties [103]. 

The proper balance between viscosity and gas evolution can be controlled by a number of factors such as a suitable type and concentration of catalyst and surfactant, the presence of a nucleating agent (not always necessary) (17,18) and control of reaction temperature (or exotherm). Additional factors that must be considered are the use of a suitable chemical blowing agent, which is especially important for the production of thermoplastic foams, and the formation of oligomers (prepolymers) which exhibit higher viscosities than monomers in the preparation of thermoset foams (e.g. polyurethane foams). 

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