Microstructure to property relations in a family of millable polyurethane fluoroelastomers

A series of segmented polyurethane fluoroelastomers based on perfluoropolyether macromers and functionalized with allyl groups is presented. Their peroxidic vulcanization behaviour was studied on both unfilled and carbon black filled compounds by dynamic rheometry. The optimal amount of allyl groups and peroxy content was determined. Formation of polyphasic structure with phase segregation of a low Tg fluorinated moiety was shown by calorimetric analysis. The low Tg value is not affected by vulcanization which, on the other hand, is effective in the elimination of any residual crystalline order of the urethane phase. The vulcanized compounds were characterized by tensile tests, dynamic-mechanical analysis, solvent swelling, compression tests and non-isothermal stress relaxation measurements. Mastercurves were successfully built based on time-temperature superposition principle. It resulted that polyurethanes based on symmetric diisocyanates show better chemical resistance and low temperature viscoelastic behaviour, and are promising candidates for the development of high performance low temperature sealing materials.