Analysis of the molecular heterogeneity of poly(lactic acid)/poly(butylene succinate-co-adipate) blends by hyphenating size exclusion chromatography with nuclear magnetic resonance and infrared spectroscopy.

The compositional and stereochemical heterogeneity of copolymers are key molecular metrics, and their knowledge is of pivotal importance for evidence based material development. Yet, while it is state of the art to determine these parameters for many petroleum based polymers, little insight exists in that regard for bio-based materials. Towards this end, size exclusion chromatography (SEC) was hyphenated with nuclear magnetic resonance spectroscopy (NMR) in an offline manner and a blend of poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) investigated. Thus, the microstructural heterogeneity could be shown with regard to tacticity of the PLA and regioregularity of the PBSA component. The results show, that the highest molar mass fraction differs in stereochemical composition from the others. It may be assumed that this is the result of misinsertions with regard to stereochemistry occurring during the catalytic polymerization of the lactide. While the content of both constituent polymers along the molar mass axis could be well studied using a univariate analysis of the infrared (IR) spectra, this method failed to profile the adipate and succinate content individually. For this purpose, SEC was coupled to IR spectroscopy in online mode and the spectra were evaluated by a multivariate protocol. Thus, the content of each monomer along the molar mass distribution could be mapped with high chromatographic resolution.

Proton conductivity and phase transitions in 1,2,3-triazole.

1,2,3-Triazole (TR) is a good proton conductor which is tidely related to formation of a hydrogen bond network along the N-HN trajectory and its self-dissociation into diH-1,2,3-triazolium and 1,2,3-triazolate. To gain a deeper understanding, the proton conductivity of TR is measured by impedance spectroscopy (IS) across its melting temperature and an additionally discovered solid-solid phase transition. The orthorhombic high temperature phase and the monoclinic low temperature modification are investigated by polarized optical microscopy, DSC- and WAXS measurements. Furthermore, the diffusion coefficients of TR are determined from IS data and measured by (1)H PFG NMR spectroscopy in the melt which allows for separate evaluation of contributions of proton hopping across the hydrogen bond network and the vehicle mechanism to the proton conductivity where the vehicles are defined as charged species generated by TR self-dissociation. Finally, the degree of dissociation of TR is calculated and the influence of the self-dissociation of TR on the proton conductivity is discussed in the context of the dielectric constant.