Diisocyanates polymerization reactions

We now report a convenient method for the interfacial polycondensation of 1,1 -bis(3-aminoethyl)ferrocene (1) with a variety of diacid chlorides and diisocyanates, leading to ferrocene-containing polyamides and polyureas. In some instances, we have been able to observe film formation at the interface. Moreover, the polymerization reactions can be conveniently conducted at ambient temperatures in contrast to earlier high-temperature organometallic condensation... 

The addition polymerization reaction of dihydroxy compounds with diisocyanates sets in on mixing the two components and gentle warming. Under proper conditions, linear polyurethanes with molecular weights up to about 15,000 can be obtained. As in the case of polyamides and polyesters, the softening point of the aliphatic polyurethanes depends on the number of carbon atoms between the urethane groups. 

Foamed-in-place polyurethane is prepared by allowing a polyol [po y(ethy ene glycol), polyester alcohols, etc.] to react with a diisocyanate in the presence of an amine catalyst. The gas which creates the foam may be a dissolved material, such as a Freon, which volatilizes during the exothermic polymerization reaction.7 A second method involves the use of water in the reaction mixture this hydrolyzes part of the isocyanate to produce an amine and C02 gas. The Freon-formed material is preferred for the insulation of low-temperature apparatus because the thermal conductivity of the foam is greatly reduced at low temperatures by the condensation of the Freon in the cells. It is probable that the longterm effectiveness of this phenomenon must be maintained by surrounding the foamed plastic with an airtight enclosure which will prevent diffusion of air into and Freon out of the cells. 

The prepolymer is formed by addition polymerization, and there are no by-products formed that have to be removed. The prepolymer chains extend by the reaction of terminal isocyanate groups (-NCO) with the diol. The mole reaction ratio of the diol to diisocyanate is normally kept in the range of one mole diol to 1.6 to 2.25 moles of the diisocyanate. A reaction ratio of one mole diol to one mole diisocyanate will produce a linear material. This type of polyurethane is normally thermoplastic. 

Carbodiimides are also used as catalysts in the formation of polyamides from dicarboxylic acids and diisocyanates. The carbodiimide catalyst is generated in situ from the diisocyanate using dimethylphospholene oxide as the catalyst. In this manner segmented thermoplastic poly(ether amides) and poly(ester amides) are obtained from the acid terminated monomers and diisocyanates by reaction polymerization processes. This reaction is best conducted in a vented extruder because carbon dioxide is the byproduct. 

Condensation polymers by the above delinition are usually produced by step-growth polymerizations but not all step-growth syntheses are condensation reactions. Thus there is no elimination product in polyurethane synthesis from a diol and a diisocyanate (cf. reaction (1-12)) ... 

Flexible Foams CO2 obtained in situ by the reaction of water with isocyanate has been the chief blowing agent for all commercially produced flexible urethane foams. The amount of water and tolylene diisocyanate (TDI) used determines foam density, providing most of the gas formed is used to expand the urethane polymer. Because water participates in the polymerization reactions leading to the expanded cellular urethane polymer, it has a very pronounced influence on the properties of foams. For better control of the foaming process most foam manufacturers employ distilled or deionized water (16). 

Polyurethanes are formed when a diisocyanate (or polyisocyanate) is reacted with hydroxyl groups at a molar ratio of 2 or higher (isocyanate hydroxyl). When the polyol and polyisocyanate are combined in the presence of a suitable catalyst, the exothermic polymerization reaction begins spontaneously. This type of synthesis is an addition polymerization. Most polyols and polyisocyanates used for manufacturing PUs are liquid at standard room temperature. Industrially, the PU synthesis reaction is rapid, and the product is a solid polymer. The reaction rate can be varied significantly by changing the catalyst type and concentration, facilitating the use of PUs in a variety of applications. ... 

Polymers in this category are synthesized by routes similar to the routes used to synthesize regular step-growth polymers. The difference, however, is that the monomer units contain a metal-metal bond. A sample step-growth polymerization reaction is shown in Eq. 7.1, which illustrates the reaction of a metal-metal bonded dialcohol with hexamethylene diisocyanate (HMDI) to form a polyurethane.4... 

There are step-growth polymerization reactions in which a small molecule is not produced (e.g., the reaction between a diol and a diisocyanate) these reactions are considered irreversible and are usually very fast, leading to high degrees of polymerization. 

The purpose of this chapter is to outline some selected polymerization reactions of mono- and diisocyanates. In a previous volume (this series, Vol. I) we described the preparation of polyurethanes and, therefore, we will not deal with this aspect in this chapter. 

Hydroxy-terminated liquid polybutadienes are prepared for reactions with diisocyanates to form elastomeric polyurethanes (see Chapter 6). Such materials can be prepared by anionic polymerizations as living polymers and then quenched at the appropriate molecular weight. These polybutadienes can also be formed by a free-radical mechanism. The microstructures of the two products differ, however, and this may affect the properties of the finished products. To form hydroxy terminated polymers by a free-radical mechanism, the polymerization reactions may be initiated by hydroxy radicals from hydrogen peroxide. 

Covalently crosslinked IPN were realized by combination of polymerization and polyaddition reactions. Generally, such IPN are prepared in the order polyaddition first and polymerization reaction second. The other sequence was demonstrated in IPN from polyethyleneglycol dimethacrylate blended with star-shaped poly[(rac-lactide)-cc>-glycolide], which was first photopolymerized and afterwards the polyesterurethane network was formed using isophorone diisocyanate [38]. While R and were reported to be above 93%, TJrans = Tg could be adjusted between -23 and 63 °C. 

Reaction polymerization reactions of isocyanates with suitable monomers can he performed in an extruder or in a RIM machine. In the latter reaction thermosets (cross-hnked polymers) are produced. In an extruder usually linear polymers are manufactured. For example from methylene di-p-phenylene isocyanate (MDI), with some macroglycols and 1,4-hutanediol as extenders, segmented polyurethane elastomers are produced in an extruder (6). However, linear condensation polymers are also produced in a vented extruder. For example from MDI, with macrodicarboxylic acids and dicarboxyhc acids as extenders thermoplastic block copolyamide elastomers are produced. The by-product of the condensation reaction, carbon dioxide, is removed in the vented extruder. The polycondensation process can also be performed in solution. For example, MDI can be added to a solution of dicarboxyhc acids in tetramethylene sulfone, with simultaneous removal of the carbon dioxide. Tetramethylene sulfone is the solvent of choice for solution polymerization of isocyanates (7). In addition to dicarboxyhc acids trimellitic acid anhydride and benzophenonetetracarboxylic acid dianhydride (BTDA) are utilized as monomers for condensation polymers. With these monomers poly(amide imides) and poly(imides) are produced. The diisocyanate-derived commercial polycondensation products are listed in Table 1. 

Because of its relatively low boiling point HDI is currently only supplied in the form of derivatives (trimer, allophanate, biuret, etc) (18). Polyrmeric aliphatic isocyanates are obtained by copolymerization of 2-isocyanatoethyl methacrylate and styrene (19). Hydroxyalkyl acrylates and methacrylates are used as monomers to form hydroxyl group containing polymers, which are cross-hnked with diisocyanates or blocked diisocyanates (20). The elusive parent dusocyanate, 0=C=N—N=C=0, is only stable at —75°C, and therefore it is not suitable as a monomer or comonomer in polymerization reactions (21). 

The term polyurethane is used to describe polymers which have been prepared by uniting intermediates containing at least two hydroxyl groups with isocyanates via the formation of a urethane link. This is a rearrangement reaction and unlike condensation polymerizations does not lead to the splitting out of a small molecule such as water. In the case of a dihydroxyl compound and a diisocyanate the reaction leads to the formation of a linear polymer ... 

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