Structure, Dynamics, and Rheological Behavior of Associative Polymers Formed by Hydrogen Bonds

In this work, a coarse-grained model is constructed to explore the structure, dynamics, and rheological behavior of associative polymers (APs) formed by hydrogen bonds (HBs). First, the structural change of HBs with the number of active groups and temperature is analyzed by calculating the bond length, angle, number, energy, and strength of HBs. Then, the phase structure formed by HBs is characterized by analyzing the number and size distribution of clusters and the coordination number per “hydrogen”. Furthermore, the dynamics of HBs and polymer chains are calculated by analyzing the time correlation function of HBs and the incoherent intermediate dynamic structure factor. The obtained relaxation time exhibits an Arrhenius dependence on the temperature. Finally, the rheological behavior of APs is explored where the change of zero-shear viscosity with the number of HBs (N_HB) or temperature (T*) follows two empirical formulas [η₀ = 0.0456N_HB + 105 and η₀ = exp (25 + 51/T* – 19.5/T^*2)]. The shear-thinning behavior is attributed to the changes in the structure and dynamics of HBs and chains. With the increase of shear rate, the weak HBs are first broken. Then, the strong HBs are weakened and broken down, which can be understood well by calculating the probability distribution function of the bond length and angle. The polymer chains are gradually reoriented, stretched, and disentangled, which is characterized by the asphericity factor and the entanglement number of chains. Interestingly, a universal scaling relationship with reduced variables is constructed between the relaxation time and the shear rate, which can be described well on the whole range of shear rates, the number of active groups, and temperatures. In summary, this work provides a novel understanding of the rheological behavior of APs formed by HBs at the molecular scale.