The Synthesis And Investigation Of Poly(butylenes Terephthalate) With Ionic Groups

Poly(butylenes terephthalate)(PBT) is one kind of polyesters which have been applied widely in different areas. At the same time much effort have been made to enhance the performance of PBT by blending and co-polymerization. Comparatively by the ionization to PBT macromolecules was rarely investigated. There are few reports on this issue.The sulfonated poly(butylenes terephthalate) (SPBT) ionomers with various contents of ionic group were prepared in this paper by the melting polycondensation from dimethyl terephalate, 5-sulfoisophthalate sodium salt and 1,4-butanediol. The sulfonated poly(butylene terephthalate) ionomers containing 4, 6 and 8 mole percent of dimethyl-5-sodiosulfoisophthalate monomer units were assigned by SPBT-4, SPBT-6 and SPBT-8 respectively. The intrinsic viscosity [η] of SPBT-4, SPBT-6 and SPBT-8 is 0.63 dL/g, 0.50 dL/g, 0.39 dL/g which was measured by Ubbelohde viscometer. It is found that the intrinsic viscosity of ionomers was lower than that of the poly(butylenes terephthalate). And the more content of ionic units, the lower of the intrinsic viscosity. The sample was analyzed by the FT-IR, an absorption peak on 628cm^-1 was found which was characteristic of the stretching vibrations of C-S bond . It confirmed that the ionic group—SO₃Na is chemically linked in the polymer chains exactly.The crystallization and melting behavior of these SPBT was studied by different scanning calorimetry(DSC). During the first heating on DSC of PBT and SPBT, an endothermic peak at 130℃is observed, which may mean the presence of ordered ionic clusters in SPBT. The melting temperature T_m decreases and the crystallization temperature T_c from the melt shifts to low temperature with increasing content of ionic groups of SPBT. The exdothermic peaks of crystallization become wider and flatter, and even duplicated, implying complex crystallization for SPBT. The modified Avrami equations are used to describe the non-isothermal crystallization kinetics of PBT and SPBT. Non-isothermal crystallization reveals that the crystallization rate of SPBT becomes smaller than that of PBT, especially at the lower cooling rates. The Avrami exponent of SPBT ionomers varies in the range of 3～4, indicating that the non-isothermal crystallization follows the homogeneous or hetergenous nucleation and three-dimensional spherulitic growth mechanism. XRD indicates that the crystalline structure formed in SPBT is as the same as that in PBT. But the crystal dimensions become smaller, especially in the side-by-side direction of macromolecular chains and related with chain direction. The crystallinity keeps almost unchanged.Rheological behaviors of the ionomers were studied systematically through a capillary rheometer. The results show that the ionomer melt is a typical pseudoplastic fluid exhibiting shear thinning phenomena in a capillary flow. When the shear stress and temperature increases, the apparent viscosity of the ionomers get down. At the same level of shear stress and temperature, the apparent viscosity of the SPBT ionomers are lower than that of the PBT. And with the ionic groups grow up, it decrease more. The relationship between temperature and the apparent viscosity of the SPBT ionomers is agreement with the Arrhenius equation. The visco-flow activation energy of the ionomers are higher than that of poly(butylenes terephthalate) extremely, indicating that the melt of SPBT is more sensitive to temperature than that of PBT.The SPBT ionomers can be spun into fibers by melt spinning using the ABEΦ25 spinning machine. SPBT reached lower spinning speed than PBT, for example 600m/min due to lower level (800m/min for PBT). The mechanical properties of the ionomer fibers were also measured. The strength at break of SPBT fibers is lower than that of PBT fibers. The elastic recovery of SPBT fibers is worse than that of the PBT fibers. Whereas the ultimate elastic recovery gets higher level than that of the instantaneous elastic recovery, which means the elastic recovery rate of the SPBT ionomers becomes slow. The sound velocity of SPBT fibers reduce with the increasing of the ionic groups. XRD analysis of the fiber shows the crystallization does not developed fully during the spinning. Some absorption peaks disappear and the crystal dimensions become smaller. It probably shows the ionic groups increase the interaction between the macromolecular chains, which retard the chain diffusion and folding before crystallization.