Interpenetrating Polymer Network of Rubbery Epoxy and Glassy PMMA: Network Inhomogeneities and Dynamic Heterogeneities

Abstract

Interpenetrating polymer networks (IPN) are model polymeric systems for vibration damping applications owing to their unique viscoelastic properties. They are characterized by presence of static frozen inhomogeneities at molecular scale and are dynamically heterogeneous at a segmental level. These fundamental and characteristic features of IPNs need to be characterized in order to deduce their structure–macroscopic property correlations. In the present study, we report sequential IPNs prepared from a polyether diamine cross-linked epoxy and triethylene glycol dimethacrylate (TEGDM) cross-linked poly(methyl methacrylate) (PMMA). Positron annihilation lifetime spectroscopy (PALS) studies revealed a decrease in free volume hole sizes with increased PMMA content in the IPNs, implying interpenetration of polymer chains at a molecular level. Dynamic mechanical analysis measurements were carried out to get insight into the structural relaxations and viscoelastic properties of the IPNs. The IPNs exhibited dissipation factor (tan δ) values >0.3 over a broad temperature (∼10–120 °C) and frequency range (20–20000 Hz), which qualify them as efficient vibration dampers. Stress strain profiles of the IPNs evolved from an elastic to a glassy response with strain-hardening characteristics as the PMMA content was increased in the IPNs. Simultaneous strengthening, stiffening, and toughening of the epoxy matrix were observed with increased PMMA content in the networks. The IPNs were also characterized for liquid water and toluene sorption characteristics to obtain mechanistic insights into the transport properties of the synthesized IPNs. Increasing water uptake and decreasing toluene sorption characteristics were observed with increased PMMA content in the IPNs. The free volume size plausibly governs the water transport properties, while toluene sorption in the IPNs could be influenced by its thermodynamic interaction with the networks. In both cases, non-Fickian sorption kinetics was observed. We posit that the present studies and results provide the basis for designing and characterizing vibration damping networks for practical applications.