Role of graded length side chains up to 18 carbons in length on the damping behavior of polyurethane/epoxy interpenetrating polymer networks

A series of novel polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites with graded length side chains were prepared from toluene diisocyanate (TDI), polytetrahydrofuran glycol (PTMG), EP, trimethylolpropane (TMP), and diol chain extenders. The effects of the side chain lengths, content, and groups on the damping properties and mechanical properties were investigated. Two damping peaks were observed in the PU/EP IPN system, indicating that the peak damping factor (tan δ) increased with increased side chain length at low temperatures. The introduction of an apolar side chain slightly narrowed the damping range. However, the side chain carrying polar groups broadened the damping temperature range. The strong H-bond interaction between the ester group of side chain and the Nsingle bondH of hard segments in PU was believed to favor microphase separation to form a larger-sized domain and induce the appearance of the relaxation peak at high temperatures. Consequently, the effective damping temperature range was broadened. The side chain content tethered in the hard segment remarkably influenced the damping properties of PU/EP IPNs both at low and high temperatures. The width and intensity of the tan δ peaks of PU/EP IPNs increased with increased side chain content. The mechanical properties (tensile strength and elongation at break) were significantly affected by the side chain content. Thus, an important method of improving the mechanical damping of elastomers by controlling the side chain molecular structure was established.