Similarities and differences in the structure of polyurethane and polyurea:
Polyurethane is a polymer material containing urethane bonds formed by chemical reactions between the terminal isocyanate compounds and polyhydroxyl compounds.
The reaction requires a certain temperature and requires catalyst. After the polymer has been solidified into a film, the polymer chain contains a variety of chemical bonds, such as carbon carbon bonds, ether bonds, ester bonds, ammonia ester bonds, and a small amount of urea bonds.
Polyamide is a polymer material with urea bond formed by reaction of terminal polyisocyanate with terminal polyamine (including resin and chain extender).
It needs no catalyst and can react quickly without heating. Spray polyurea (SPUA) should be heated to adjust the viscosity so as to facilitate uniform film formation. After curing, the polymer chain contains carbon carbon bond, ether bond, urea bond, ester bond, urethane bond and so on.
1, the same point
(1) when polyurethane is solidified into film, after curing with polyurea, the types of chemical bonds contained in the molecular chains are the same or similar.
(2) both polyurethane and polyurea must be made of prepolymer or semi prepolymer or oligomer containing isocyanate terminated. Polyurea is also known as a special polyurethane or high mechanical polyurethane.
2, different points
1) although the polyurethane and polyurea are solidified into films, the chemical bonds are the same or similar, but the functional groups that play a key role in the physical properties of the polyurethane rubber membrane are the amino ester bonds, and the functional group which plays a key role in the properties of the polyurea is urea bond. There are ammonia ester bonds and urea bonds in polyurethane and polyurea, but the number of the ammonia ester bond is much more than the urea bond in the rubber film solidified after the polyurethane. The properties of the polyurethane are mainly determined by the ammonia ester bond, and the number of urea bonds in the rubber film after the polyurea floor is more than the number of the amino ester bond, and its performance is mainly determined by the urea bond.
(2) urea bond strength greatly exceeds the strength of urethane bond, and urea bond is stable.
3) for the common spray polyurethane (urea) or heterozygous polyurea (hybride) in the market, besides the amino polyether and the amido chain extender, there are also hydroxyl groups (such as polyether, polyester, etc.) as well as the catalyst in the two components. The amount of ammonia in heterozygous polyurea should be between 20% and 80% in the crosslinking agent, and if it is lower than 20%, it is called polyurethane.
4) during the curing process of single component polyurethane, 1 water molecules consume 2 NCO and produce 1 urea bonds. The number of amino ester bonds in the molecular structure is still much more than the number of urea bonds, and the mechanical properties are much lower than that of single and double component polyurea (including heterozygous polyurea). Even if the latent curing agent is added, the urethane bond is still larger than the urea bond number. The common latent curing agents are hydroxyl and amino terminated compounds. After unsealing, they react with NCO (isocyanate) to form urethane bonds and urea bonds. Latent curing agent only inhibits the number of CO2 bubbles and inhibits the formation of vesicles. A considerable part of NCO still depends on the reaction of water molecules to form urea bonds, but the speed and quantity of CO2 produced are greatly reduced without stomatal formation. The crosslinking point has the urea bond and the ammonia ester bond.