Processing of polymers using reactive solvents : thermoplastic polyurethane (TPU) as reactive solvent using the ceiling temperature phenomenon

The processability of high Tg polymers or polymers possessing a high viscosity can be improved by using (volatile) solvents, as they decrease the Tg and the viscosity of the system. Major disadvantage, however, is that the solvent has to be removed after processing in order to retain the properties of the polymer. A solution to this problem can be found in the use of reactive solvents (monomers) which, after processing, are polymerized into a constituent of the final material. By choosing the right conditions, the polymer can be retained as the matrix material and will dominate the properties of the final product. Conventionally, reactive solvents which need to be polymerized at a substantially high temperature and with the aid of another component are used, such as epoxy resin or styrene. However, in industrial applications like injection molding, these systems are difficult to use due to the high temperature of polymerization (high mold temperature) and the lack of control of polymerization in the (high temperature) extruder. By using the concept of ceiling temperature, the problems mentioned above can be overcome. Above the ceiling temperature, no polymerization of the solvent will occur and if started from a polymer, a depolymerization of the polymer will take place. Cooling the system below the ceiling temperature will result in a polymerization of the solvent again and consequently in the desired phase separation. Two conditions have to be fulfilled for such a low temperature polymerizing solvent, i.e. miscibility of the intractable polymer and the monomers from the depolymerized polymer solvent and a high enough degree of depolymerization of the polymer solvent (low enough ceiling temperature). In this present investigation, it is shown that these two conditions are met for Thermoplastic Polyurethanes (TPU) and that therefore systems with TPU as reactive solvent have the potential to be used in injection molding applications. Results concerning Polystyrene/TPU as a model system and Polyphenylene ether/TPU systems will be discussed