The Polymer Brush of Sub-Nanometer Molecular Clusters: Surface Click-Chemistry for Precise Modulation of...

Molecular granular materials (MGMs) assembled from structurally precise molecular clusters exhibit unique viscoelasticity; however, the capability in modulating the viscoelasticity remains limited. Herein, the surface functional group is proposed as a key factor governing the viscoelasticity of MGMs. The vinyl-functionalized POSS-based polymer brush (PolyVPOSS) is synthesized as a versatile template for the systematic introduction of diverse surface groups via efficient thiol-ene chemistry. The polymer brushes of POSS derivatives bearing ethylhexane, phenyl, carboxyl, and tert-butyl groups, respectively, are synthesized and broadly tunable viscoelasticity ranging from viscous liquid, elastomers to glass can be observed. The hierarchical structures are studied using small angle X-ray scattering while their multi-level relaxation dynamics are probed using broadband dielectric spectroscopy. The viscoelasticity of all the polymer brush samples is quantified via rheological measurements, and they are further correlated with the relaxation dynamics for the correlation among surface functional group-relaxation dynamics-apparent viscoelasticity. This work sheds insight into the microscopic mechanical viscoelasticity of MGMs while it also provides a new opportunity to the design of structural materials via surface modulation of MGMs.