Flexible foams synthesis

Hie most representative member of this class of polyesters is the low-molar-mass (M 1000-3000) hydroxy-terminated aliphatic poly(2,2/-oxydiethylene adipate) obtained by esterification between adipic acid and diethylene glycol. This oligomer is used as a macromonomer in the synthesis of polyurethane elastomers and flexible foams by reaction with diisocyanates (see Chapter 5). Hydroxy-terminated poly(f -caprolactonc) and copolyesters of various diols or polyols and diacids, such as o-phthalic acid or hydroxy acids, broaden the range of properties and applications of polyester polyols. 

Moreover, flexible foams are characterized by utilization of special emulsifiers in their synthesis yielding an open-cell architecture, whereas for rigid foams emulsifiers are chosen that create more closed-cell structures. As diisocyanate for both types, the commercially available mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate is especially suitable. If foam formation is to take place at room temperature, and especially when hydroxy compounds with secondary hydroxy groups are used [poly(propylene glycol)s], the presence of a catalyst is generally required (see Sect. 4.2.1). 

Di- and poly-isocyanates are mainly used in the production of polyurethane rigid or flexible foams (for insulation and in furniture), adhesives, sealants, surface coatings, elastomers and fibres [2007,2072,2165], whilst mono-isocyanates are employed in the synthesis of substituted ureas and carbamates (Section 4.7.3) for medicinal, agricultural and other... 

The esters of adipic add are also used in the synthesis of thermoplastic elastomers and of certain flexible foams. The most widely used glycols for the esterification of adipic add are ethylene glycol and 1,4-butaoedioL... 

By the hydrolysis of a flexible foam based on toluene diisocyanate (TDI) one obtains toluene diamine (2,4 and 2,6 isomers), the polyether triol and, of course, carbon dioxide. The difficulty of the process is the separation of the amine. The amine may be used for TDI synthesis (after a previous purification), or be transformed into a valuable rigid polyol (aminic polyol) by alkoxylation with PO and EO. 

A spectacular increase in all properties was observed in elastic polyurethanes (especially in polyurethane elastomers, but in flexible foams too), by using polyethers obtained with dimetallic catalysts (DMC) instead of potassium hydroxide. There are obtained directly from synthesis, polyethers with a very low unsaturation, in essence polyethers with a very low content of polyether monols. 

Polyurethane foam synthesis can be modified by additions of PEG in such a way that an open-cell, very flexible, highly elastic foam is produced, for example, for upholstery. 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

In conclusion, to obtain a good, resilient, flexible PU foam without collapse, with high rise and free of blow holes, it is necessary that the PO used for the polyether synthesis be free of high MW PPO contaminants. 

DMC catalysts are considered to be the ones that perform best at this time for PO polymerisation initiated by hydroxyl groups. Bayer developed the first continuous process, with a very high productivity, for the synthesis of polyether polyols with DMC catalysts (IMPACT Catalyst Technology). In a short and simple production cycle, a large variety of polyether diols of very low unsaturation for elastomers, sealants, coatings and low monol content polyether triols destined for flexible polyurethane foams are obtained. This is one of the best developments in the last few years in the field of polyether polyol synthesis [2],... 

Thus, glycerol, the most important starter for the synthesis of polyether polyols for flexible PU foams and for polyether for rigid foams is produced by the hydrolysis of natural triglycerides (esters of glycerol with fatty acids with C6 to C22 carbon atoms), from vegetable or animal resources (reaction 17.1) [1]. Large quantities of glycerol appear in bio-diesel production, by transesterification of natural oils with methanol. 

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. 

GC alone can be a valuable monomer for the synthesis of hyperbranched poly(hydroxyether)s (Scheme 25). In case of polymerization, GC, containing a l,3-dioxolan-2-one ring and hydroxyl group in a single molecule, is considered a latent cyclic AB2-type monomer. The anionic ROP of the GC, which proceeds with CO2 liberation, leads to a branched polyether. l,l,l-Tris(hydroxymethyl)propane or other multihydroxyl molecules are usually used as a initiator-starter and central core of the polyether. The hyperbranched polyglycerol structure is obtained by slow addition of the cyclic carbonate monomer at above 150 °C. Such polymers are characterized by a flexible polyether core and a multihydroxyl outer sphere. They are suitable for preparation of acrylic resins for dental applications or additives for polyurethane foams. Hyperbranched poly (hydroxyether)s from biscyclic carbonate with phenol group (2, Scheme 24) were also reported. 

From Section 3.3, it was shown there are a large number of monomers and oligomers available for polyurethanes. It is often said that if cost was not of concern, then urethane-based polymers could be tailored to replace most polymers for applications that did not demand too high a service temperature [28]. Polyurethanes, besides adhesives and sealants applications, can be found as foams (rigid, flexible, micro-cellular), elastomers, and encapsulants which differ slightly in raw materials. However, processing parameters and additives make feasible a diverse synthesis of this material. 

The original synthesis of ABT-839 (2) efficiently provided material for early studies and provided the flexibility to vary the sidechains in order to study SAR. However, e route required at least three chronmtographic separations, which prohibited synthesis of kilogram quantities of material. The penultimate intermediate was purified by column chromatography prior to the final ester hydrolysis and the final product was isolated as an amorphous foam. We were seeking an efficient process that addressed the concerns of purification of intermediates, allowed for isolation of a crystalline final product and could be used to synthesize kilogram quantities of material. 

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