Synthesis And Characterization Of Sulfonated PBT And PHB/SPBT Liquid Crystalline Ionomers

In this paper, the poly(butylene terephthalate) based ionomers and liquid crystalline ionomers with various contents of sodium sulfonate groups were prepared by melt copolycondensation. The molecular structures of these two kinds of polymers were characterized, the influence of the ionic groups on the rheological, crystalline, thermal and mechanical properties of these polymers was also investigated. Moreover, the enhancement effect of LCIs on pure PBT was tested.Sulfonated PBT ionomers (SPBTs) with various contents of ionic groups were prepared from the melting polycondensation of dimethyl terephalate, dimethyl 5-sulfoisophthalate sodium salt and 1,4-butanediol. The existence and the content of sodium sulfonate groups in the SPBTs were identified by means of FTIR and elemental analyses. It was found that the intrinsic viscosities, i.e., the molecular weights of the SPBT ionomers decreased with the increasing ion contents, therefore, the ionomers became rigid and brittle, and their impact properties seemed a little weaker than that of PBT. However, the SPBTs showed betterelongation properties. The results of DSC and DMA analyses showed that the glass transition, the crystalline and the melting temperatures of the SPBT ionomers decreased with the incorporating of ionic groups. The isothermal crystallization kinetics of SPBTs was investigated via depolarized light intensity method. It was found that ionic groups reduced the uniformity and the mobility of SPBT macromolecular chains, resulting a longer induced nucleation time and a slower crystalline velocity. Nevertheless, the larger spherulites were ultimately formed in SPBT samples. The rheological analysis indicated that the non-Newtonian behavior became stronger in the samples with more ionic groups, and the melting flowing active energy of SPBTs seemed more sensitive to temperature and shear rate.The SPBT/PHB liquid crystalline ionomers (LCIs) were also obtained from the copolymerization of p-acetoxybenzoic acid (the acetylated product of p-hydroxybenzoic acid, PHB) and SPBT. It was found from the FTIR and NMR analyses that there existed a portion of molecular chains enriched in PHB in LCIs. The enrichment of PHB came from its self-polycondensation, and the more ionic groups in SPBT or the more PHB was used, the more PHB enrichment. The liquid crystalline characteristics of SPBT/PHB copolyesters was verified by using polarizing microscopy observations, it was also found that the presence of ionic groups in the copolyesters had no influence on the forming of liquidcrystalline phase. The incorporation of ionic groups reduced the thermal stabilities of LCIs, however, the sample with more PHB enrichment showed higher thermal stability. The composites of LCIs and PBT were prepared through melt blending. Though the molecular weights were rather low, SPBT/PHB LCIs showed good enhancement effects on the pure PBT.