Polyurethane Amine extender

Phase II The phase I studies showed the potential of HER as a polyurethane chain extender. Excellent elastomers resulted with no processing problems. In phase II, the optimum catalyst and catalyst concentration was determined by curing one prepolymer, B-625, using a variety of tertiary amine and organo-tin catalysts. The results are shown in Tables VII and VIII. 

Immediately add the chain extender (ethylene diamine), which has been diluted in water slowly to the aqueous polyurethane/urea dispersion. Typically chain extend only 80-90% of the actual free NCO groups because some will be lost due to reaction with water. As an alternative, the amine extender may be added to the water prior to dispersing the neutralised prepolymer. 

STRUCTURE EFFECTS OF AROMATIC AMINE EXTENDERS ON THE PROPERTIES OF POLYURETHANE ELASTOMERS ... 

BORN L and hespe h, On the physical crosslinking of amine-extended polyurethane urea elastomers a crystallographic analysis of bis-urea from diphenyl methane-4-isocyanate and 1,4-butane diamine . Colloid Polym Sci, 1985, 263, 335-341... 

Only a few commercial uses for TDA per se have been found. In epoxy curing appHcations, 2,4- I DA has been used as a component of a eutectic mixture with short chain aUphatic glycidal ether resins (46) as well as by itself (46,47) TDA (46) and single isomers (47) are also used as amine curatives. TDA can be used as a chain extender in polyurethanes (48,49). TDA is cited as a monomer in making aromatic polymers with unique properties, eg, amorphous polyamides (50), powdered polyamides (51), and low melting, whoUy aromatic polyamides (52). 

Woodhouse described a degradable polyurethane prepared with a novel amine chain extending agent. As with the insertion of lactic acid into the backbone, bio-degradability was achieved, but the fragments appeared problematic. Thus, while biodegrading polyurethanes are fairly simple to prepare, one must be aware of the product to which a polyurethane degrades. The use of TDI as the isocyanate would clearly raise concerns from the FDA. 

Polyurethanes offer a convenient method by which iimnobilization of enzymes can be affected. Prepolymers are polymers with active end groups. While the primary purpose of the isocyanate end groups is serving as chain-extending agents, they also react with the amines that characterize an enzyme backbone. Thus, as many of the studies cited will show, the reaction sequence is (1) preparation of an aqueous solution of the enzyme and (2) emulsification of the solution with the prepolymer. The reaction time is on the order of 0.5 hours compared to the 24 hours required by some methods. 

Among the new being consider for reactive processing into polyurethane-based materials, the so-called polyester amines, in combination with chain extenders, which also contain amine groups, are especially promising.19 Using these materials allows the synthesis of polymers with polyurea instead of polyurethane bonds. This results in materials with improved impact strength and lower water absorption. 

Diamines may be introduced as short chain extenders. As the amine reacts rapidly (Eq. 2.23), hindered aromatic amines must often be used to allow a controllable reaction. Polyurethane ureas are formed. 

TDI-based polyurethanes produce the best properties when further chain-extended with amine-based curatives. The overall properties can be increased if only the 100% 2,4 isomer is used. These materials are generally not suited for use with food. MDI-based polyurethanes have good overall properties and as they are predominately cured with a diol, they can obtain FDA approval more readily. 

Polyurethanes are made by extending chains of a prepolymer made from a macro diol and a diisocyanate. The prepolymer is further extended with a diol or an amine curative. The long chains form a solid which is relatively weak. When the part is given a longer heat treatment, the molecules align themselves and intermolecular bonds (hydrogen bonding) are formed. At this point the full mechanical properties are established and the material, if suitably formulated, has excellent mechanical and chemical properties. 

Thermoset polyurethanes are cross-linked polymers, which are produced by casting or reaction injection molding (RIM). For cast elastomers, TDI in combination with 3,3,-dichloro-4,4,-diphen5lmethanediamine (MOCA) are often used. In the RIM technology, aromatic diamine chain extenders, such as diethyltoluenediamine (DETDA), are used to produce poly(urethane ureas) (47), and replacement of the polyether polyols with amine-terminated polyols produces polyureas (48). The aromatic diamines are soluble in the polyol and provide fast reaction rates. In 1985, internal mold release agents based on zinc stearate compatibilized with primary amines were introduced to the RIM process to minimize mold preparation and scrap from parts tom at demold. Some physical properties of RIM systems are listed in Table 7. 

Reaction with difunctional amines (see the next paragraph) allows the formation of poly (urethane-co-urea) and further extends the versatility of the segment architecture. For further control of the structure, a prepolymer is formed. The reaction, such as the polyurethane reaction shown above, is carried out with excess di-isocyanate so that an isocyanate-terminated prepolymer is obtained. The isocyanates used are typically aromatic, such as toluene di-isocyanate. This prepolymer is then reacted with a short-chain diol or diamine (for a polyurea) to form the final polymer. 

After ammonolysis, ammonia is evaporated and can be reused after liquefaction, while degradation products of polyurethane hard segments (e.g., amines and chain extenders) and urea are removed by extraction. The pure polyol is left in the reactor. It can be removed mechanically or by extraction with liquid ammonia in which it is soluble. The recovered amines can be converted to the corresponding isocyanates and can be reused, along with polyols, in the same applications as before. A flow scheme of the recycling process is shown in Figure 6.9. 

The two components are kept in temperature-controlled tanks, with pumped re-circulation when injection is not taking place. For the polyurethane system, one tank contains an isocyanate (usually MDI) and the other a mixture of polyol, chain extenders, catalyst and mould release (and possibly blowing agent or reinforcing additives). An amine catalyst accelerates the initiation of the polymerisation, while an organotin catalyst... 

A major use of polyurethanes is in the manufacture of foams, both rigid and flexible. The chain-extension reactions described previously are normally used when elastomeric-type products are required, but for foams, the chain-extender molecule can be omitted and polyols with an average functionality in excess of three are used. The reaction is base-catalyzed by tertiary amines or oigano tin compounds (e.g., stannous octanoate) and must also include a blowing agent in the reaction mixture. This can be achieved by adding controlled quantities of water to the system and making use of the reaction ... 

Waterborne polyurethane resins are produced from maleinised monoglyceride (MMG) of sunflower oil, hydroxy-terminated polybutadiene, toluene diisocyanate and ethylene diamine. The carboxylic acid groups of MMG are neutralised by triethyl amine, making the resin water dispersible. The monoalkylated castor oil (MCO) or dehydrated castor oil (DCO) is treated with a polyether glycol at 120°C, followed by the addition of IPDI and DBTDL. To obtain a series of aqueous polyurethanes, butane diol and dimethylol propionic acids (DMPA) are added and the mixture heated to 70°C for two hours to produce a NCO-terminated pre-polymer which forms salt with triethylamine, giving a water-soluble polymer. The reaction mixture is dispersed in water and a chain extender, ethylene diamine, is added. Two aqueous polyurethanes, MCPU and DCPU, are finally obtained from MCO and DCO, respectively. 

In some applications of interest to us, notably solid fuel rocket propellants, polybutadiene is used as the soft segment of a polyurethane rather than as bulk polymer. Hence, our studies of the role of amines in adhesion have been extended to include systems with polyurethanes derived from functionalized liquid polybutadiene. 

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. 

Polyurethane adhesives comprise a polyisocyanates, polyols and chain extenders, which can be amines or alcohols. The most common polyisocyantes are based on aromatic... 

So far, this method was not extended to the post cure processes of PUs. However, if its use is intended, there are difficulties to be expected. The overlapping of the NMR nitrogen resonance signals as isocyanate with amine and urea with biuret mentioned by these authors [337] will be complicated here even more by overlapping with other additional nitrogen signals characteristic to a polyurethane system, like urethane and possible allophanate nitrogens [337-340],... 

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