Mechanical Reinforcement by Interfacial Layer in Phase-separating Associating Telechelic Polymers*

Associating polymers capable of forming reversible bonds exhibit macroscopic properties (e.g. unique viscoelastic behavior, self-healing capability etc.), which are governed by their microstructure. Here, we investigate the structure and dynamics of short telechelic PDMS polymers with H-bonding end groups. Small angle X-ray scattering measurements indicate phase separation (clustering of functional end groups) due to the polarity difference between polymer backbone and sticky end groups. The presence of the clusters significantly alters the viscoelastic behavior of these materials, resulting in extremely long rubbery plateau. Using dielectric spectroscopy and an approach developed earlier for polymer nanocomposite, we estimate the thickness of an interfacial polymer layer around these clusters. The dynamics of this interfacial layer is almost an order of magnitude slower than segmental dynamics of bulk-like polymer. Using the interfacial layer model (ILM) analysis, we find that shear modulus of this interfacial polymer layer is ~100 MPa. Our analysis reveals that phase-separating telechelic associating polymers are quite similar to polymer nanocomposites, and interfacial layer plays a critical role in their mechanical and viscoelastic properties.