Self-Assembly of Ureido-Pyrimidinone Dimers into One-Dimensional Stacks by Lateral Hydrogen Bonding

Ureido-pyrimidinone (UPy) dimers substituted with an additional urea functionality self-assemble into one-dimensional stacks in various solvents through lateral non-covalent interactions. 1H NMR and DOSY studies in CDCl3 suggest the formation of short stacks (<10), whereas temperature-dependent circular dichroism (CD) studies on chiral UPy dimers in heptane show the formation of much larger helical stacks. Analysis of the concentration-dependent evolution of chemical shift in CDCl3 and the temperature-dependent CD effect in heptane suggest that this self-assembly process follows an isodesmic pathway in both solvents. The length of the aggregates is influenced by substituents attached to the urea functionality. In sharp contrast, UPy dimers carrying an additional urethane group do not self-assemble into ordered stacks, as is evident from the absence of a CD effect in heptane and the concentration-independent chemical shift of the alkylidene proton of the pyrimidinone ring in CDCl3

Multiscale organization of thermoplastic elastomers with varying content of hard segments

Thermoplastic elastomers (TPEs) based on segmented block-copolymers containing poly(tetrahydrofuran) (pTHF) and terephthalate-based diamide groups (T4T) were synthesized via polycondensation. While pTHF is known to be flexible and amorphous at rest, the more rigid T4T crystallized in different ways depending on both chain composition and sample preparation conditions. Increasing the content of hard-segments (HS) from 5 to 20% in weight leads to a substantial increase of the melting point Tm by more than 60 °C. We have systematically investigated the multiscale (1 Å - 50 nm) organization of the HSs (of fractions from 5% to 20%) by means of DSC, WAXS and (ultra) small angle X-ray scattering (U)SAXS. By increasing HS content, hence the rigidity of the chain, scattering experiments unambiguously show the formation of bigger and better defined ribbon-like crystallites, as well as the densification of the network they form. We propose a scenario for rationalizing the local T4T-HSs packing and the crystallites anisotropy at the mesoscale (1–10 nm) for HS fraction above 5%. Moreover, following in-situ the crystallization of TPEs with large HS fraction (20%), we highlight the presence of “persistent aggregates” present at T > Tm and study the ribbon-like crystallites growth mechanism during cooling from the melt state