Polyurethane elastomers polar groups

A series of these rubbers possess polar groups consequently, the corresponding elastomers do not swell in oil. Polyurethane rubbers and polysulfide rubbers, as well as the already mentioned nitrile and chloroprene rubbers (Table 37-5), belong to the good oil-resisting rubbers. Moderate oil resistance with simultaneously improved heat resistance is shown by chlorosulfonated ethylene, acrylic, silicone, and fluorine rubbers. 

The contribution which the different types of polar groups make to the properties of polyurethane elastomers depends in part upon their ability to enter into strong hydrogen-bonded associations. The substituted urea linkage, formed by the reaction of an isocyanate with an amine, is regarded as exceptional in its contribution to the physical properties, and it is therefore a preferred component in many bulk elastomers where the structural irregularity introduced by the use of a non-symmetrical diisocyanate or polyol is compensated by the strong urea interactions. 

The very polar urethane and urea groups and the very strong hydrogen bonding between these groups make polyurethanes very resistant to hydrocarbons and oils. This is one of the biggest advantages of PU elastomers over the conventional rubbers. 

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