Polyether diols functionality

The hot curing process normally uses polyether diol precursors with molecular weights of 3,000 to 5,000 g/mole. We can control the stiffness of the foam by adjusting the average number of isocyanate groups on the chain extender molecules. The higher the functionality of the isocyanate molecules, the more crosslinked, and hence stiffer, will be the product. 

Both KOH and water present in glycerol are sources of polyether diols which decrease the functionality of the polyether triol [2-13] ... 

The single polyol from this group that needs special attention is sorbitol, which is delivered in the form of an aqueous solution of around 70%. It is possible to use solid sorbitol, which is delivered in the form of crystalline monohydrate, but it is much more expensive than liquid sorbitol (calculated as a dry substance) and more difficult to handle and melt. The polyols delivered as aqueous solutions need water distillation under vacuum, in order to limit the formation of polyether diols during the reaction with PO, which decreases the functionality of the resulting polyether polyols. There are two possibilities to distill water until a relatively low level (0.1-0.5%) is reached or to make a controlled distillation of water, by stopping the distillation at a level of water which, together with sorbitol should lead to a functionality of 4.5-5 hydroxyl groups/mol. 

Figure 21.1 Functionality of polyether diols, PO homopolymers, obtained in anionic...

The blocked isocyanate function of aminimides also allows their use as polyurethane adhesives. Thus bis(aminimides) crosslink with polyester or polyether diols to yield a range of elastomers dependent upon the structure of the bis(aminimide) and the co-reactant chosen. For example, bis(aminimides) mixed with polyhydroxyl components can provide stable, single-package prepolymer compositions which yield polyurethanes on heating without the problem of isocyanate moisture sensitivity which can plague polyurethane applications. 

In the early 1950s, flexible foams were made by the prepolymer process. In this process, a prepolymer is prepared by reaction of a diisocyanate with a diol, usually a linear polyether diol similar to those described in Section IV.A for elastomers. The prepolymer polyether diisocyanate, usually a poly(propylene oxide) diisocyanate, has a molecular weight in the range of 1000 to 2000. Water is used as a chain extender in making the prepolymer and also to provide branch sites to increase the functionality of the prepolymer through formation of biuret linkages. 

Another type of sealant uses a combination of chemistry to yield a product useful as a sealant. This chemistry is a marriage of silicone and organic chemistry known as a polyether silicone. The basic polymer for this type of sealant is the reaction product of a polyether diol with a diisocyanate followed by further reaction with an amino-functional alkoxy silane. Thus, the central portion of this polymer is a polyether that is terminated with a urethane linkage that leads to the terminal group which is an alkoxy silane. This polymer can cure by the methods described above for a standard silicone but it contains the properties of a polyether. As with the normal silicones described above, these materials also have to be reinforced in order to obtain the tensile properties desired for a sealant. The same list of fillers as described above can be used in polyether silicones. Adhesion promoters such as silane coupling agents, diluents of various sorts, plasticizers, and catalysts are also added to these materials. 

The principal polymeric plasticizers are the polymer hydrocarbons and the polyesters. The condensation products of diols and dicarboxylic acids, belonging to the polyester group, are most important. Higher functional compounds, like triols and tricarboxylic acids, are less important as are polyethers, polyacetals, and polymeric acids. 

The processes described in Table 2 present a peculiar interest in the working out of new materials as polyurethanes. These last polymers are very often based on macro diols coming from polyethers or polyesters, a-co functional polyolefins being relatively uncommon. Hence, Rhein and Ingham [139] prepared macrodiols by ozonization of polyisobutylene in CC14 at... 

The polyether esters are made by typical melt polymerization procedures. A prepolymer is first prepared by interchange of the methyl ester of one or more aromatic dicarboxylic acids with a mixture of a polymeric diol and enough short-chain diol for an overall 50% excess of hydroxyl functionality (Figure 2). A titanate catalyst is generally used. Methanol is fractionated from the reaction mixture to avoid loss of... 

The polyethers obtained by the anionic polymerisation of PO initiated by glycerol are not trifunctional, having a lower functionality than 3, but usually in the range 2 < f < 3. The diols and monols decrease the functionality. The functionality is lower for high MW polyethers and for the polyethers obtained at higher polymerisation temperatures. In Figure 4.6, one observes the strong polyether triol functionality decrease as the polyether MW increases. 

The polyether triol functionality as function of unsaturation and of diol content can be calculated using the following formula ... 

In a polyether triol composition the following are present nj = mols of monols, of functionality = 1 n2 = mols of diols, of functionality f2 = 2 n3 = mols of triols, of functionality f3 = 3... 

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