Entanglement Relaxation of Linear Polymers: Revisiting Constraint Release

Entanglement relaxation of linear polymers is affected by constraint release (CR) competing with reptation. Recently, Hannecart et al. [Polymers 2023, 15, 1569] focused on polymers of various chemical structures, polystyrene (PS), polyisoprene (PI), polybutadiene, and poly(methyl methacrylate) (PMMA), and concluded that the CR time τ_L,CR of the long chains normalized by their entanglement number Z_L and the Rouse time of the entanglement segment τ_e is determined only by the entanglement number of the short chain Z_S irrespective of the chemical structure. However, the values of Z_L and Z_S should have unavoidably included experimental uncertainties, which disturbs a rigid conclusion. Thus, this study focused just on the linear viscoelastic moduli G* of monodisperse polymers of various chemical structures, PS, PI, PMMA, and poly(t-butyl styrene) (PtBS). We were able to find several pairs of chemically different but viscoelastically equivalent monodisperse polymers, and found that τ_L,CR of the dilute long chain was different even when the components were viscoelastically indistinguishable in their monodisperse state: The CR relaxation was slower in the order of PS (slowest) < PMMA < PI< PtBS (fastest) by a factor of 3-4 in total, which unequivocally shows the non-universal character of CR. An origin of this nonuniversality can be found, for example, in a chemistry-dependent number of local CR hopping sites per entanglement segment [Graessley, Adv. Polym. Sci. 1982, 47, 68-117].