Comblike Ionic Complexes of Poly(γ-glutamic acid) and Alkanoylcholines Derived from Fatty Acids

A series of ionic complexes with almost stoichiometric composition have been “synthesized” from bacterial poly­(γ-glutamic acid) and alkanoylcholines derived from fatty acids with 12, 14, 16, and 18 carbon atoms. The complexes were stable up to temperatures close to 200 °C and were non-water-soluble but readily soluble in organic solvents. In the solid state they adopted the biphasic structure typical of comblike systems with the polypeptide chains arranged in sheets and periodically separated by a paraffinic phase which was partially crystallized for C14, C16, and C18. The window width of the layered structure was estimated by SAXS to be within the 3.6–4.5 nm range, and WAXS showed that the alkyl tails were crystallized in a hexagonally packed lattice with a <i>d</i>₁₀₀ spacing of 0.41 nm. These complexes displayed reversible melting of the paraffinic phase in the 40–65 °C range at temperatures with values increasing with the length of the alkanoyl group. A slight expansion of the intersheet distance occurred at melting followed by contraction upon heating at higher temperatures but without significant alteration of the layered structure. The ¹³C CP-MAS NMR analysis revealed the underlying polymethylene <i>anti</i>-to-<i>gauche</i> conformational conversion that takes place at the thermal transition. An energy-based simulation study of the crystallization process afforded a molecular picture of the complex and evidenced the favoring effect of the choline structure on the packing of the alkyl side chains

Bio-Based Aromatic Polyesters from a Novel Bicyclic Diol Derived from d‑Mannitol

2,4:3,5-Di-<i>O</i>-methylene-d-mannitol, abbreviated as Manx, is a d-mannitol-derived compound with the secondary hydroxyl groups acetalized with formaldehyde. The bicyclic structure of Manx consists of two fused 1,3-dioxane rings, with two primary hydroxyl groups standing free for reaction. A homopolyester made of Manx and dimethyl terephthalate as well as a set of copolyesters of poly­(butylene terephthalate) (PBT) in which 1,4-butanediol was replaced by Manx up to 50% were synthesized and characterized. The polyesters had <i>M</i>_w in the 30 000–52 000 g mol^–1 range and a random microstructure and were thermally stable up to nearly 370 °C. They displayed outstanding high <i>T</i>_g with values from 55 to 137 °C which steadily increased with the content in Manx. Copolyesters containing up to 40% of Manx were semicrystalline and adopted the crystal structure of PBT. Their stress–strain parameters were sensitively affected by the presence of carbohydrate-based units with elongation at break decreasing but tensile strength and elastic moduli steadily increasing with the degree of replacement