Polyurethane (PU) is used in the aromatic diamine extender chain agent alkaline is weaker than aliphatic diamine, with - NCO reactivity is relatively low, so need certain gel time, and can make the PU elastomer with good physical properties, used as a molded urethane aromatic diamine, usually in the molecular steric groups or electron-withdrawing groups is introduced to reduce the reactivity to improve casting time.
The most commonly used aromatic diamine chain extenders are 3, 3-dichloro-4, 4-diaminodiphenyl methane or dichlorodiphenylamine methane, or MOCA.MOCA has the following disadvantages in use:
1. MOCA under normal temperature for solid, when using, need to be heated to above 100 ℃.
2. When prepolymer is added after melting, the reaction is too fast due to high temperature, and the viscosity increases rapidly, which makes the raw materials difficult to mix and the product quality declines.
3. As a result of too fast reaction, -nco generates urealytic acid ester bonds based on amine ester reactions and generates cross-linking, which shortens product life.
4. MOCA is suspected to cause cancer, which will have adverse effects on human body and environment.
5. MOCA will degrade when exposed to air, sunlight and high temperature in storage, which will affect the appearance and quality of PU.
DMTDA is a new liquid curing crosslinking agent developed in 1980s. DMTDA has no physiological degeneration and carcinogenicity, and has no harm to human safety.
|tensile strength/kgcm-z||540||460||GB/T531 -92|
|rebound resilience/%||45||40||GB/T1681 -1|
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