Influence Of Nano-TiO₂ On Structures And Properties Of 4GT-PTMO Elastomers

In this paper, a series of modified Poly(ether ester) elastomers (named as 4GT-PTMO) were prepared by the in-situ polymerization of nano TiO₂, dimethyl terephthalate (DMT), 1,4-butandiol (BD), and poly(tetramethylene oxide) (PTMO). The influence of nano-TiO₂ on the crystallization characteristics and melting rheological properties of 4GT-PTMO were investigated by means of differential scanning calorimetry (DSC), dynamic mechanical test (DMA) and dynamic rheological analysis. Moreover, the elastic fibers were spun from nano-TiO₂ or glycerin (GL) modified 4GT-PTMO, and the latter was a branched copolymer, The mechanical and elastic recovery properties of those fibers were studied via the stress-strain test.According to the DSC results, the melting temperature (T_m) of hard block (butylene terephthalate segments) shifted to lower temperature and the T_m of soft block (PTMO segments) shifted to higher temperature with increasing content of nano-TiO₂. Meanwhile, the crystallinity of hard segments decreased with the increasement of TiO₂, while that of soft segments increased. The onset crystallization temperature of hard segments from melt shifted slightly to higher temperature, but the end temperature of crystallization shifted to lower temperature, suggesting a slower crystallization due to the incorporation of nano-TiO₂. When the content of TiO₂ was comparatively high, the crystallization of soft segments would take place at higher temperatures. DMA results showed that the glass transition temperature of the soft segment got up with the increase of TiO₂ content, and the dissipative peak got broaden. According to the non-isothermal crystallization kinetic analysis, the crystallization rate constant decreased and the half crystallization time of both hard and soft segments increased with the increasing TiO₂ content. It deduced that TiO₂ acted not only as a heterogeneous nucleating agent, but also a crosslink centre because the high surface adsorption ability of nano-particles. Therefore, on the whole the crystallization rate of 4GT-PTM0 became slow.From the dynamic rheological analysis, it was found that the storage modulus of 4GT-PTMO/TiO₂ with 0.5%wt TiO₂ showed almost the same tail end behavior as the pure 4GT-PTMO under the low strain frequency, which revealed that the blocked 4GT-PTMO with small content (0.5%wt) of nano-TiO₂ still exhibited micro-phase separation. However, when 1.0-1.5%wt nano-TiO₂ was added, 4GT-PTMO/TiO₂ didn't show phase separation.The mechanical properties test showed that the modified 4GT-PTMO elastic fiber with 0.5%wt nano-TiO₂ was similar to GL modified one, i.e., they both had high elastic recovery ability, and their elongation at break increased because of modification. The velocity and modulus for sonic transmission of elastic fibers with different drawing multiples were investigated, and it was found that the sonic transmission slowed down for those two fibers compared with unmodified ones at the same drawing multiple, which should be owing to the interaction between macromolecules in 4GT-PTMO established by nano-TiO₂ or GL. This just was the expected structure for enhancing elastic recovery.