Multiscale organization of thermoplastic elastomers with varying content of hard segments

•Original interpretation of the T4T unit WAXS pattern based on a 2D-growth approach.•Evidence for the thickening of crystallites with increasing the chain rigidity.•Evidence for a crystal conformational transition with increasing the chain rigidity.•Evidence for the presence of H-bonds above the crystallites melting point (SAXS).•Proposition of a new growth scenario based on temperature resolved-SAXS tests.

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.

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