First, the impact of raw materials on the heat resistance of polyurethane elastomer
Polyurethane elastomers consist of soft segments (oligomeric polyols, which are mainly classified into polyester, polyether, and polyolefin polyols) and hard segments (diisocyanates and chain extenders). The relative molecular mass of oligomer polyols is polydisperse, and polyisocyanates are often mixtures of multiple isomers. The presence of isomers can destroy the regularity of the hard segments, resulting in a reduction in the heat resistance of the elastomer. Strict control of the purity of the raw materials and the reduction of the molar fraction of groups having poor thermal stability such as biuret and allophanate can improve the heat resistance of the elastomer.
Second, the effect of polymerization conditions on the heat resistance of the elastomer
The thermal stability of urea and urethane groups is greater than the thermal stability of allophanates and biurets, which indicates that the mole fraction of urea and urethane groups in the elastomer molecule is increased, and the urea group is reduced. The mole fraction of the acid ester group and the biuret group can improve the thermal stability of the elastomer, that is, the process conditions are strictly controlled, in particular the amount and purity of the reactants, so that the reaction produces as much urea groups and carbamates as possible. Base, it is of great significance to improve the heat resistance of the elastomer. The use of diamine chain extension to produce urea groups, the control of NCO groups to react with urea groups to form biurets, and the use of aromatic diisocyanates can effectively increase the heat resistance of polyurethane elastomers.
The reaction of polyurethanes generally includes one-step method, prepolymerization method and semi-prepolymerization method. One-step method is relatively simple, but the product molecular structure is often irregular, poor performance, prepolymerization and semi-prepolymerization method is better.
Third, to improve the heat resistance of polyurethane elastomer deformation method is varied, in practical applications should be based on product performance indicators and process requirements for a reasonable choice to determine a feasible route. Although improving the heat resistance of polyurethane elastomers has always been a very active topic in the field of polyurethane elastomers, and a great deal of research has been carried out, the polyurethane elastomers with excellent comprehensive properties such as heat resistance and mechanical properties are still less, and the overall level is still At the laboratory development stage. The development of new modification systems and the enhancement of the industrialization of results are still the major research topics in the field of polyurethanes.
Good heat resistance, PPDI, NDI, TODI, and CHDI, if you want to make prepolymer, NDI activity is too high, it is not realistic at present (It is said that Burberry Bayer's prepolymer research institute successfully synthesized storage stability NDI prepolymer), the rest is okay. In general, thermal stability and yellowing are required, and CHDI is better. PPDI with better heat resistance and dynamic mechanical properties is better. When TODI is chain extended with amines, performance is close to that of NDI.