The morphology of flexible polyurethane matrix polymers

Abstract

The morphological evolution of a flexible polyurethane foam is a complicated process involving many ingredients and multiple simultaneous reactions and processes [1,2] (Fig 4.1). In most cases, the basic polymer-forming reaction occurs between the isocyanate and a polyol. This is a simple addition process which, when extended to polyfunctional reagents, provides a direct route to covalently crosslinked polymers. Density reduction is provided via the in situ generation of a gas or via the volatilization of a low boiling point blowing agent. Historically, foamers have used chlorofluorocarbons for this purpose; however, ecological considerations have caused the industry to re-evaluate alternate density reduction technologies. In many present-day foam applications, the density-reducing gas is formed in situ from the reaction of isocyanate with water. The basic chemistry for a water-blown foam is outlined in Fig 4.2. The reaction products, which include urethanes, ureas, amides, allophanates, biurets, carbodiimides and isocyanurates, subsequently associate to generate an auxiliary network. The latter associations generally lead to a polymer having multiphase molecular morphology.