Diamines chain extenders

Chain extenders are usually low molecular weight symmetrical diols or diamines. Chain extenders react with isocyanates in the same way as polyols do, but because they are low molecular weight, a high concentration of hydrogen-bonded molecules can associate and phase out of the polyol to form plastic-like domains called hard segments . Hard segments will be discussed in Section 4. Some of the more common diol and diamine chain extenders are shown in Table 3. 

The chain extension step may then take place in the water phase. Hydrazine and ethylene diamine are commonly used chain extenders for waterborne urethane dispersions. The isocyanates react with the diamine chain extenders much faster than with the water, thus forming polyurea linkages and building a high molecular weight polymer. More detailed information regarding the synthesis and process of making waterborne polyurethane dispersions is found in Dieterich s review article [58]. 

Amine-terminated siloxane oligomers have also been utilized in the synthesis of various siloxane-amide and siloxane-imide copolymers, High molecular weight siloxane-amide copolymers have been synthesized by the solution or interfacial co-polymerization of siloxane oligomers with sebacoyl chloride or terephthaloyl chloride respectively 1S5,165). In some reactions diamine chain extenders have also been utilized. Thermal and dynamic mechanical characterization of these copolymers have shown the formation of multiphase systems160). Compression molded films displayed very good elastomeric properties. 

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

If no polyol is used and only amine-terminated polyethers with a diamine chain extender are employed, a polyurea RIM system is obtained. 

Garret, J. T., X. Ruijian, J. Cho, and R. James. "Phase Separation of Diamine Chain Extended Poly(Urethane) Copolymers FTIR Spectroscopy and Phase Transions." Polymer 44 (2003) 2711-2719. 

When the prepolymer chain is extended with a diol, the polymer formed has only urethane linkages. The polymer formed with the diamine chain extender is strictly a polyurethane polyurea. The first urethane component is from the initial chain extension when the prepolymer is prepared. A diamine curative will form urea linkages (Figure 2.3) between chains. 

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. 

Figure 6. Because of the rapid increase in dynamic viscosity of Halthane 88-2 poly(urea-urethane) adhesive caused by a higher concentration of HMDI- aromatic diamine chain extender, the initial viscosities are difficult to determine accurately.

Urea linkages have been monitored during the extrusion production of a polyurethane-urea, through doping with a fluorescent aromatic diamine chain extender, whereas soluble poly(arylene etherjs, thioethers and sulfones have been synthesized which emit strongly in blue and red regions. Brownian dynamics have been used to determine the distribution of fluorescent resonance... 

Solventless, elastomeric coatings were reported by Bonk et al. (169). The sprayable compositions were based mainly on diethylene glycol adipates, Isonate 143-L, and various diamine chain extenders and curatives. Airless Binks spray guns were employed in the... 

Unflirtk . [UOP] Aronudc diamine chain extender for polyurethanes. 

These contain a methylene bis(p-phenyIdiisocyanate) (MDl) hard segment, an ethylene diamine chain extender, and a polyether soft segment in mole ratios of 2/1/1 respectively. The soft segment materials were polyethyleneoxide (PEO) and polytetramethyleneoxide (PTMO), both of 1000 molecular weight, and polydimethyIsiloxane (PDMS) of 2000 molecular weight. In this paper, these polymers will be refered to as PEO-PEUU, PTMO-PEUU and PDMS-PEUU respectively. These were dissolved in N,N-dimethyl acetamide (DMA) to make a 0.1 wt.% solution. 

Chlorotetrafluoroethane CFC-12 substitute as diluent in sterilizing gas Chlorotetrafluoroethane chain extender Toluene-2,4-diamine chain extender, PU... 

This TPE is a segmented polyurethane and is reported to be not significantly different from biomer in chemistry and molecular weight. It is a polytetra-methyleneoxide-based aromatic polyurethane urea with mixed aliphatic and cycloaliphatic diamine chain extenders. A copolymer of... 

Specifically designed as an 80 Shore A durometer TPE, this is a diamine chain extended version of Corethane . Coremer solution cast films have a low initial modulus and high flex fatigue life. Information as to longterm biostability is not available at this time (Tables 4.4 and 4.13). 

Examples of diamine chain extenders (Fig. 1.10) include 2,5-bis-(4-amino-phenylene-l,3,4-oxadiazole) (DAPO), 4,4 -diamino-dibenzyl (DAB), 2,6-diamino-pyridine (DAPy) or 4,4 -methylene-diamine (MDA). 

In a second stage of our study we compared the DAB and MDA based materials (PUDB and PUDM from above) with other PUUs obtained by using the same macrodiols, (polyester PEA or polyether PTMO) but the diamine chain extenders 2,5-bis-(4-amino-phenylene)-I,3,4-oxadiazole (DAPO) or 2,6-diaminopyridine (DAPy). The materials were obtained similarly as in the case of the TDA and MDA... 

DIAMINE CHAIN-EXTENDER CONTROL OF THE PHYSICAL PROPERTIES OF TOLUENE DIISOCYANATE-BASED ELASTOMERS... 

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