What is the difference between polyester polyurethane and polyether polyurethane in terms of reaction principle and reaction result?
1. The principle of reaction
Polyester polyurethane is obtained by the reaction of polyester and isocyanate, wherein polyester is obtained from polybasic acid (such as adipic acid, phthalic acid, maleic acid, etc.) and polyol (such as ethylene glycol, propylene glycol, Trimethylolpropane, etc.) polycondensation reaction, can be divided into two kinds of hydroxyl polyester and carboxyl polyester, of which the polyurethane foam used is hydroxyl polyester, that is, excessive polyol.
Base polyester (excess polyol): 2OH-R-OH +HOOC-R'-COOH——HO-R-OCO-R'-COO-R-OH
Carboxyl polyester (excess polyacid): OH-R-OH +2HOOC-R'-COOH——HOOC-R'-COO-R-OCO-R'-COOH
Polyether polyurethane is obtained by the reaction of polyether polyol and isocyanate, wherein polyether polyol is composed of active hydrogen-containing initiator (such as alcohols, amines) and olefin oxide (such as ethylene oxide, propylene oxide) obtained by ring-opening polymerization.
Polyether polyol: R-OH + nPO——R-(-O-CH-CH3-CH2-O)n-H
Both types of polyurethanes are finally formed by the reaction of hydroxyl groups with isocyanates to form carbamates.
R-NCO +R'-OH——RNHCOOR'
Therefore, in terms of reaction mechanism, the biggest difference between the two types of polyurethanes is the difference between whether the soft segment molecular chain mainly contains an ester bond (-COO-) or an ether bond (-C-O-C-).
2. The reaction results
Polyester polyurethane has high mechanical strength, good oil resistance and heat resistance, so it is mainly used in microcellular foam soles, as well as elastomers, coatings and artificial leather.
Due to the presence of ester bonds (unsaturated double bonds), the stability of polyester polyurethanes in hydrolysis resistance, low temperature resistance, oxidation resistance, acid resistance and alkali resistance is not as good as that of polyether polyurethanes.
3. Development trend
Due to the high viscosity of polyester polyol itself, poor miscibility with other components, difficult construction, and high cost of raw materials, its application in the field of polyurethane is not much. On the contrary, the application of polyether polyurethane is very wide. , but mostly used in synthetic foam.
In recent years, in order to improve the technological properties of polyester polyols, oxyalkylene compounds (such as PO\EO) have been introduced into the polyester polyol molecules, so that the soft segment molecular chain has both ester bonds (-COO-) and ether bonds (-COO-) C-O-C-), the polyurethane obtained from this new polyol has the characteristics of polyester and polyether polyurethane at the same time.
