Entropy-Enhanced Mechanochemical Activation for Thermal Degrafting of Surface-Tethered Dry Polystyrene Brushes

Dry polymer brushes have attracted great attention because of their potential utility in regulating interface properties. However, it is still unknown whether dry polymer brushes will exhibit degrafting behavior as a result of thermal annealing. Herein, a study of the conformational entropy effect on thermal degrafting of dry polystyrene (PS) brushes is presented. For PS brushes with an initial grafting density (σ_pⁱⁿⁱ) of 0.61 nm^-2, degrafting behavior was observed at 393 K, and the equilibrium σ_p was approximately 0.14 nm^-2 at 413 K. However, for brushes with σ_pⁱⁿⁱ ≤ 0.14 nm^-2, thermal degrafting was not observed even if the temperature was increased to 453 K. Furthermore, we found that the degrafting rate was faster for PS brushes with higher σ_pⁱⁿⁱ and higher molecular weights when σ_pⁱⁿⁱ > 0.14 nm^-2. Our findings confirmed that degrafting is a mechanochemical activation process driven by tension imposed on bonds that anchor the chains to the surface, and the process is amplified by conformational entropy.