Effect of soft segment structure on properties of polyurethane elastomers
【Abstract】Using four different soft segments, i.e., polytetrahydrofuran diol (PTMG), polycaprolactone diol (PCL), hydroxyl-terminated polybutadiene with high cis-1,4 content (HTPB), and commercial hydroxyl-terminated polybutadiene produced by free radical polymerization (FHTPB), four kinds of polyurethane elastomers (PUEs) were prepared by two-step solution polymerization. The effects of soft segment structure on mechanical properties and thermal properties at room temperature and low temperature were investigated by tensile test, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It is found that the tensile strength and elongation at break of the four PUEs at low temperature (−30 °C) are superior to those at room temperature. This is not only related to the autofrettage effect induced by crystallization of soft segment at low temperature, but also associated with the increase in the degree of micro-phase separation between the soft and hard segments. Compared with the other three kinds of PUE, the HTPB-PUE has the soft segment with the lowest polarity and glass transition temperature (Tg), so the micro-phase separation is in the highest degree, and the elastomer has the most excellent flexibility. Even at −30 °C, the elongation at break of the HTPB-PUE is up to 660%. PCL-PUE and PTMG-PUE are rigid because their soft segments are easy to crystallize and their degree of micro-phase separation between soft and hard segments is low. The cyclic tensile testing indicates that HTPB-PUE and FHTPB-PUE still have excellent elasticity at −30 °C. The results from DSC and DMA show that the Tg of HTPB-PUE is much lower than those of the other three PUEs, and the value from DSC is about −103 °C. The initial thermal decomposition temperatures of the four PUEs are very similar, and are all around 270 °C.
【Keywords】 polyurethane; elastomer; soft segment; structure; properties;
(Translated by LIN LY)
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