Interpenetrating Polymer Networks with Polyurethane and Methacrylate-based Polymers

Abstract

Interpenetrating polymer networks (IPNs) were synthesized with polyurethane (PU) and methacrylate-based polymers in order to create a transparent device with high toughness for potential applications in high-impact scenarios. This research consisted of four parts with the first involving successful synthesis of an IPN based on PU and poly(methyl methacrylate) (PMMA). Aspects studied included the following: aliphatic versus aromatic isocyanates in the PU phase, the presence of an inhibitor in the PMMA phase (sequential versus simultaneous reactions), curing profiles, and ratios of PU:PMMA. Samples which included an aliphatic isocyanate, PU content around 80 wt%, and a sequential polymerization demonstrated the best material properties, ultimately due to increased phase compatibility between PU and PMMA. Further analysis on the IPNs involved manipulating the PU network to enhance polymer compatibility and material properties. One approach involved using diols of different molecular weight in the PU phase. Both the PU and the IPN networks’ morphologies were consequently affected. Increasing the chain length also increased the molecular weight between cross-links and decreased cross-link density. Fracture toughness did improve with an upper limit in the molecular weight of the diol. Another method in altering the PU network consisted of changing the diol:triol ratio. In other words, the ratio of the linear chain to the cross-linking agent of the PU phase was varied. Morphological changes did take place, which in turn affected material properties, but the results were not as pronounced as when the molecular weight of the diol was increased. The last approach was, to some extent, different than the other methods in the creation of IPNs. Instead of synthesizing a full-IPN, where only physical cross-links existed between the polymer networks, a graft-IPN was synthesized with physical and chemical cross-links connecting PU and PMMA. This was accomplished by replacing the PMMA phase with a copolymer of bisphenol A glycidyl methacrylate (BisGMA) and triethylene glycol dimethacrylate (TRI-EDMA). The ability of the hydroxyl groups in BisGMA to react with the isocyanate groups in PU allowed cross-link points to exist between the two phases. Increased compatibility resulted, but further analysis is needed to reduce the brittleness of the materials.