We investigated telechelic poly(dimethylsiloxane) (PDMS) with different hydrogen-bonding end-groups and varying chain length in the melt state by means of broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC), rheology and small-angle X-ray scattering (SAXS). Depending on the type of hydrogen-bonding end group, -NH2, -OH, -S-COOH, or -NHCO-COOH, we observe characteristic similarities and differences in structure, dynamics and viscoelastic properties of these associating polymers. All systems exhibit an increase of the glass transition temperature Tg with decreasing MW. Only in the amide-acid (NHCO-COOH) terminated system, a 2nd Tg is found which indicates phase separation. This is corroborated by the SAXS measurements and also the BDS experiments. As a result, the shear viscosity of PDMS-NHCO-COOH is significantly higher than for the systems with other end groups, even after scaling with Tg. Additionally, the shear modulus exhibits an extended rubbery plateau of high magnitude in the -NHCO-COOH terminated systems. In contrast, PDMS-S-COOH shows only a short rubbery plateau. This suggests, that not just the end-group (-COOH in both case) but also the linker group (-NHCO- vs -S-) plays an important role. Only the -NHCO-COOH groups aggregate strongly leading to a pronounced phase separation as evident from the SAXS measurements; the absence of higher order peaks suggests that the spatial arrangement of the aggregates is not highly ordered.

Interplay of structure, dynamics and viscoelastic properties in supramolecular networks of telechelic polymers

2019 Spring National Meeting

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