Polyurethane, synthesis reactions

The transition metal catalysed addition of HCN to alkenes is potentially a very useful reaction in organic synthesis and it certainly would have been more widely applied in the laboratory if its attraction were not largely offset by the toxicity of HCN. Industrially the difficulties can be minimised to an acceptable level and we are not aware of major accidents. DuPont has commercialised the addition of HCN to butadiene for the production of adiponitrile [ADN, NC(CH2)4CN], a precursor to 1,6-hexanediamine, one of the components of 6,6-nylon and polyurethanes (after reaction with diisocyanates). The details of the hydrocyanation process have not been released, but a substantial amount of related basic chemistry has been published. The development of the ligand parameters % and 0 by Tolman formed part of the basic studies carried out in the Du Pont labs related to the ADN process [1],... 

Some investigators who studied polyurethane synthesis proposed that both the forward and the reverse reactions were important. For example this approach was assumed for the formation of linear polyurethane,49 and the following kinetic equation was derived ... 

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)) ... 

Complexes of organotin with amidines have been found to be excellent catalysts for the preparation of polyurethane foams, which do not have the disadvantage of any amine odor and, in addition, delayed onset of the isocyanate-hydroxyl reaction An example of a mercapto-delayed organotin catalyst is 2,2,4,4-tetrakis(alkyl)- l,3,2,4-dithia-stannetane.55 Amine salts of amino acids, tertiary amino acids, and tertiary amino acid-nitrile compositions, have been found to be effective as delayed action catalysts for polyurethane synthesis. They are particularly effective when used in combination with an organometallic compound, such as an organotin. ... 

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. ... 

Chain branches in stepwise polymerization may occur due to side reactions such as the addition of an -OH to a double bond in unsaturated polyester synthesis. Alternatively, chain branches can be a delibemte addition such as in polyurethane synthesis where a functionality greater than 2 is brought to bear (e.g. by using a triol chain extender) so that chain branching can occur. In systems of stepwise polymerization in which the reagents are polyftinctional these branches will lead to the occurrence of crosslinks and gelation. This is... 

The reaction between isocyanates and alcohols, the most important reaction involved in polyurethane synthesis, is an exothermic reaction and leads, as mentioned before, to production of urethanes [1-26] ... 

As in all polycondensation reactions, in polyaddition reactions (for example in polyurethane synthesis), the molar ratio between the reactive group (in our case between [-NCO]/ [hydroxyl groups]), has a very strong influence on the MW of the resulting polyurethane polymer. The maximum MW is obtained at an equimolecular ratio [-NCO]/[OH] = 1 [29]. A small excess of one reactant (isocyanate or hydroxyl groups), drastically reduces the MW of the resulting polyurethane (Figure 2.7). 

The presence of the polyether monol leads to very modest properties of polyurethanes based on polypropylene glycols obtained by anionic catalysis. In polyaddition reactions involved in polyurethane synthesis a monofunctional polyether is a chain stopper and... 

As a consequence of the outstanding properties of polyurethane as a porous material and therefore for synthesis of membranes, research continues focused not only on environmental fields but also in diverse areas such as medical devices or adhesives. Therefore, there is a potential area to develop polyurethane-separation materials as membranes. The use of naturally based polyurethane monomers during synthesis reactions [polyol, isocyanates, and chain extenders), are also key factors to explore in future to control morphological, mechanical, and thermal desirable properties. In addition the modification of polyurethane with potential natural absorbent biopolymers is an emergent research line that has demonstrated successful results [9,81,82]. 

Reaction injection molding (RIM) is suitable for some step-growth polymerization processes in which no condensation byproducts are generated, and reactions are very rapid (e.g., polyurethane synthesis from diisocyanates and diols or multifunctional alcohols) ... 

The chemo-enzymatic synthesis of polyurethanes has been reported through the inter-esterification of castor oil and linseed oil at ambient temperature, using lipase as a catalyst and foUowed by treatment of the inter-esterified product with TDI. In the first step, partial esters are prepared by transesterification of soybean and linseed oils with n-butanol in the presence of lipozyme (a lipase) as the catalyst. The partial esters are then reacted with different diisocyanates to obtain a series of polyurethanes. The reaction of polyhydroxy compounds (transesterification reaction between different compositions of castor oil and glycolysed poly(ethylene terephthalate)) with diisocyanates offers a polyurethane network for new insulating coating applications. ... 

In polyurethane synthesis, amines are used both as chain extenders and as curing agents. The chemical reactions that occur and the products that form are well known (9-11). The questions that this study addressed were two. How does the structure of the amine used affect the adhesive properties of the resulting polyurethane and how can the observed effects be explained This paper describes the synthesis and characterization of a new elastomeric polyurethane that shows remarkably high adhesion to glass and other substrates. A positive effect of amine surface treatment of the substrates on the adhesion of the polyurethane to the substrates is also reported. The results are interpreted in terms of the structure of the amines and of the polyurethane formed. 

A practical route to reduce the effects of photo-degradation in PUs (as in the case of other polymers) is the addition of suitable light stabilizers by different ways. The most used procedure is the additive stabilization method. A more effective method to increase the maintenance of the stabilizer in the polymer is the chemical bonding of these compounds to the macromolecular chain even in the course of polyurethane synthesis. Some attempts to introduce in such way the stabilizers in polymers are known. Thus, a benzotriazole UV absorber was mixed with a prepolymer containing isocyanate groups and the chain extender directly into moulding machine (cone. 0.5%) [64, 323]. The stabilizer can be also mixed into polyol component before its reaction with the isocyanate component. The stabilizer that usually contains OH groups could form chemical bonds with the macromolecular chain in some extent [324]. 

Although polyurethane synthesis can be effected by reaction of chloro-formic esters with diamines and of carbamic esters with diols ... 

Polyurethanes, also called polycarbamates, are synthesized by the reaction of a diisocyanate with a diol. Experiments are usually carried out in solutions. The following is an example of polyurethane synthesis ... 

CatalgU-Giz H, Giz A, Alb A, Reed W. Absolute online monitoring of a stepwise polymerization reaction polyurethane synthesis. J Appl Polym Sci 2001 82 2070-2077. 

Figure 4.13 Nonisocyanate urethane reactions (a) example of the formation of cyclic carbonate and the reaction with polyamines servers as a new polyurethane synthesis route (b) representative coupling reactions between hydroxyl group and amino group that form a urethane bond ...

For a monomer to support FP in a solvent, the enthalpy of the reaction must he sufficiently high that dilution does not lower the front temperature below a front-sustaining value. Dimethylbenzene can be used with polyurethane synthesis. ... 

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