Polyols trifunctional

Products intermediate to the flexible and rigid foams may be obtained from castor oil (a trihydroxyl molecule), synthetic triols of moderate molecular weight and polyesters with a moderate amount of trifunctional hydroxyl compound in the strueture. Current practice, however, is to use tipped polyols of the type used for flexible foams with MDI. Semi-rigid foams are used for such purposes as crash pads, car steering wheels and packaging equipment. 

The ATPEs have a poly(propylene oxide) backbone widi amine endgroups, as shown in Scheme 4.4. There are several routes to such materials,25 but the only one in current commercial production is die direct amination of polyether polyols. A line of uretiiane-grade ATPEs is made by Huntsman under the tradename Jeffamine. Mono-, di-, and trifunctional products are available in molecular weights up to 5000 g/m. 

These results have been fit to experimental data obtained for the reaction between a diisocyanate and a trifunctional polyester polyol, catalyzed by dibutyltindilaurate, in our laboratory RIM machine (Figure 2). No phase separation occurs during this reaction. Reaction order, n, activation energy, Ea, and the preexponential factor. A, were taken as adjustable parameters to fit adiabatic temperature rise data. Typical comparison between the experimental and numerical results are shown in Figure 7. The fit is quite satisfactory and gives reasonable values for the fit parameters. Figure 8 shows how fractional conversion of diisocyanate is predicted to vary as a function of time at the centerline and at the mold wall (remember that molecular diffusion has been assumed to be negligible). 

Crosslinking of polyurethanes proceeds in different ways depending on the stoichiometry and choice of reactants and reaction conditions. For example, an isocyanate-terminated trifunctional prepolymer is prepared by reaction of a polyol and... 

It is shown that model, end-linked networks cannot be perfect networks. Simply from the mechanism of formation, post-gel intramolecular reaction must occur and some of this leads to the formation of inelastic loops. Data on the small-strain, shear moduli of trifunctional and tetrafunctional polyurethane networks from polyols of various molar masses, and the extents of reaction at gelation occurring during their formation are considered in more detail than hitherto. The networks, prepared in bulk and at various dilutions in solvent, show extents of reaction at gelation which indicate pre-gel intramolecular reaction and small-strain moduli which are lower than those expected for perfect network structures. From the systematic variations of moduli and gel points with dilution of preparation, it is deduced that the networks follow affine behaviour at small strains and that even in the limit of no pre-gel intramolecular reaction, the occurrence of post-gel intramolecular reaction means that network defects still occur. In addition, from the variation of defects with polyol molar mass it is demonstrated that defects will still persist in the limit of infinite molar mass. In this limit, theoretical arguments are used to define the minimal significant structures which must be considered for the definition of the properties and structures of real networks. 

In most cases, linear prepolymers are used for the production of elastomers. Gas evolution via dry polyols or diamines is therefore not encouraged. When a foam is required, however, a slight adjustment is made in the construction of the prepolymer. We referred to it earlier when we discussed polyfunctional polyols. By including a trifunctional alcohol in the prepolymer recipe or by using a polyol from a trifunctional initiator (e.g., trimethylol propane), a three-dimensional character is introduced into the prepolymer. 

When the polyols are trifunctional or higher, they form thermoset polyurethanes. 

Flexible foam. This is made by mixing long trifunctional polyol with isocyanate to form the polyurethane, and adding a little excess isocyanate and water to the reaction to produce carbon dioxide which produces the foam. The largest use is in furniture, with smaller amounts in auto seating, mattresses, rug underlay, textiles, and packaging. 

Materials Two commercial polypropylene glycols (polyols) of different functionality were used. The trifunctional polyol is Union Carbide NIAX 16-56, and the difunctional polyol is Union Carbide NIAX 2025. Each has an equivalent weight approximating 1.00 kg. The polyols were dried with bubbling dry nitrogen while... 

Network Synthesis (4) Solid MDI was weighed into a flask and an equivalent amount of polyol added. The mixture was heated to about 40°C to dissolve the MDI. The mixture was then cooled to room temperature and degassed for several minutes under vacuum in order to remove dissolved air. Catalyst was then added and the contents of the flask mixed under vacuum to ensure uniformity and then poured into a mold. All operations were carried out in a dry glove bag to minimize reaction with atmospheric water. The cross-linking process was also carried out in dioxane solution at 70% volume fraction of solids. Polyurethane networks with different crosslink densities were prepared by varying the ratio of difunctional and trifunctional polyols. All samples were extracted with dioxane to remove unreacted and uncrosslinked materialbefore swelling. 

If a flexible foam is required, then longer, more flexible polyols and trifunctional cross-linking monomers are used, whereas higher-cross-link densities and short-chain polyols tend to form more rigid foams. 

Chart 11.3 Structure of part of a network formed by the reaction of a difunctional epoxide with a trifunctional polyol. 

A multistep reaction, polyaddition, is a polyreaction of at least two bifunctional or higher functional compounds. Polyaddition can result in either linear polymers (thermoplastics) or cross-linked plastics (duroplastics), depending on the specific functionality. Cross-linked products are obtained by means of a reaction of a bifunctional reactant with a trifunctional one. The more polyfunctional the reactant, the more closely meshed the cross-linking will be. That is why the polyols in polyurethane or epoxy resin production are frequently replaced by polyesters and polyethers containing large numbers of OH groups. Polyaddition, like polycondensation, is a multistep reaction. Fig. 4. Important polyadducts include linear and cross-linked polyurethanes as well as epoxy resins (see [2]). 

Chem. Descrip. Trifunctional polyol (e-Caprolactone triol)... 

The adhesive used was a model semi-structural PU, similar to one described in an earlier work [7]. The two component formnlation consisted of methylene bis-4-cyclohexyl isocyanate prepolymer and trifunctional polyols with molecnlar masses in the range 500-900. A small amount of tin catalyst (UL-28, Witco Chemicals) was also present. The PU was used as control without additives and was modified by the following silanes ... 

Castor oil is a natural polyol and its glyceryl esters consist of 90-95% ricinoleic acid and 5-10% oleic, linoleic and other fatty acids. Castor oil is approximately 80% trifunctional and 20% difunctional (the average hydroxyl functionality = 2.8 equivalent). Ricinoleic acid in castor oil is treated with ethylene glycol, diethylene glycol and triethylene glycol at 230°C to obtain a series of difunctional polyester polyols. ... 

Using this technique, a large variety of polyurethanes have been prepared from different vegetable oils. Natural polyols like castor oil (generally trifunctional) are directly reacted with diisocyanates to obtain branched polyurethanes, although it is difficult to control the reactivity. However, bifunctional castor oil can be polymerised with diisocyanates in the presence of suitable chain extenders and catalysts to produce polyurethanes in a more controlled manner (Fig. 6.4). A castor oil polyol-based polyurethane network can also be prepared from epoxy terminated polyurethane pre-polymer with 1,6-hexamethylene diamine. Epoxy terminated pre-polymer is obtained by the reaction of glycidol and isocyanate terminated polyurethane pre-polymer of castor oil polyol, poly(ethylene glycol) (PEG) and 1,6-hexamethylene diisocyanate. ... 

Lactide and y-caprolactone are copolymerized in the presence of a multifunctional polyol. For example, a diol such as ethylene glycol, may be included to produce a bifunctional hydroxyl terminated polymer, or a triol, such as trimethylolpropane, may be used to produce a trifunctional pol mier hydroxyl terminated polymer. 

When the difunctional precursors (diisocyanate, polyol and extender) are allowed to react in a stoichiometric amount, a thermoplastic PU is formed. Thermosetting PU are made by using excess diisocyanate (excess diisocyanate reacts with a urethane structure to form allophanate bonds) or by using a trifunctional extender like glycerin or trimethylol propane [92-94]. The unique feature of PU resin is that the change in UPE between crosslink offers a wide change in properties, especially the strain (which reflects flexibility). For example, a PU system with a molecular weight between two... 

These amine-terminated polyols are available under the trade name Jeffamines with various molecular weights such as Jeffamine D-2000 (difunctional), Jeffamine T-3000 (trifunctional), Jeffamine T-5000 (trifunctional). 

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