Polyurethane CatalystThe editor sorts out the similarities and differences in the molecular structures of polyurethane and polyurea.
Polyurethane is a polymer material with urethane bonds formed by a chemical reaction between a terminal isocyanate compound and a polyhydroxyl compound. This reaction requires a certain temperature and a catalyst. After the polymer material formed is solidified into a film, the polymer chain contains a variety of chemical bonds, such as carbon-carbon bonds, ether bonds, ester bonds, urethane bonds, and a small amount of urea bonds.
Polyurea is a polymer material with urea bonds formed by the reaction of terminal polyisocyanate and terminal polyamine (including resin and chain extender). It does not require a catalyst or heating to react quickly. Spray polyurea (SPUA) needs to be heated to adjust the viscosity and facilitate uniform spraying and film formation. After curing, the polymer chain contains carbon-carbon bonds, ether bonds, urea bonds, ester bonds, urethane bonds, etc.
1. Similar points
1) After polyurethane is cured to form a film and polyurea is cured to form a film, the polyurethane contained in the molecular chain The types of chemical bonds are the same or similar.
2) Whether it is polyurethane or polyurea, it must first be made into a prepolymer, semi-prepolymer or oligomer containing isocyanate terminal groups. Some people also call polyurea a special polyurethane or a polyurethane with high mechanical properties.
2. Differences
1) Although polyurethane and polyurea contain the same or similar types of chemical bonds after they are cured into films, However, the functional group in the polyurethane rubber film that plays a key role in its physical properties is the urethane bond, while the functional group that plays a key role in its performance after curing of polyurea is the urea bond. There are urethane bonds and urea bonds in both polyurethane and polyurea, but since the number of urethane bonds greatly exceeds urea bonds in the cured rubber film of polyurethane, its performance is mainly determined by urethane bonds; while polyurea flooring The number of urea bonds in the cured rubber film exceeds the number of urethane bonds, and its performance is mainly determined by the urea bonds.
2) The strength of the urea bond greatly exceeds the strength of the urethane bond, and the urea bond is very stable.
3) For the common spray polyurethane (urea) or hybrid polyurea (hybride) on the market, in addition to using amino polyether and amino-terminated chain extender in the two-component, there are also hydroxyl groups substances (such as polyether, polyester, etc.) and catalysts. The amount of ammonia in hybrid polyurea should be 20% to 80% in the cross-linking curing agent. If it is less than 20%, it is called polyurethane.
4) During the curing process of single-component polyurethane, one water molecule consumes 2 NCO and generates 1 urea bond. The number of urethane bonds in the molecular structure still greatly exceeds the number of urea bonds, and its mechanical properties Much lower than single- and two-component polyureas (including hybrid polyureas). Even if a latent curing agent is added, the number of urethane bonds is still greater than the number of urea bonds. Common latent curing agents are compounds with both hydroxyl and amino groups blocked at the same time. After being unblocked, they react with NCO (isocyanate) to form urethane bonds and urea bonds. The latent curing agent only suppresses the number of CO2 bubbles and the generation of visible bubbles. A considerable part of NCO still relies on the reaction of water molecules to form urea bonds, but the speed and amount of CO2 produced are greatly reduced, and no pores are formed. The cross-linking points include urea bonds and urethane bonds.
The above is the introduction of the polyurethane catalyst editor, I hope it will be helpful to everyone.
