Interplay of rubber network theory with the damping behavior of crosslinked polyurethanes

Network formation (branching) theory was used to examine the relationships between network structure and concomitant sound and vibration damping. For a series of model polyether-based polyurethane networks with varying stoichiometry and composition, the glass transition temperature T_g, was found to increase with increasing concentration of elastically active network chains, EANCs, as well as the ratio of branch OH group concentration to the total OH group concentration ρ. The values of (tan δ)_max, the peak height of tan δ at T_g, linearly decrease with increasing concentration of EANCs, regardless of the ρ values. However, the loss area (LA), equal to the integral of the linear loss modulus-temperature curve, is independent of the concentration of EANCs and/or ρ. Utilizing group contribution analysis techniques, the value of the main chain -O- group contribution, LA_-O-, is 19.1 GPa·K/g, a rather large value. This finding gives insight into why polyether urethanes are preferred for many damping applications.