SynopsisThe kinetics and heat transfer during the curing of a polyurethane-polyester interpenetrating polymer network (IPN) were investigated experimentally and theoretically. A model based on the additivity rule of constituent ingredients was used to predict the IPNs reaction kinetics and heat transfer. Compared with the adiabatic temperature rise measured during reaction injection molding and the temperature profiles measured during a casting process, the model prediction is close to the experimental data. Deviations of model prediction from experimental results were found in the comparison of reaction rate profiles measured by differential scanning calorimetry. This suggests that reaction interactions may exist in the polymerization system.

Kinetics of simultaneous interpenetrating networks (SIN) composed of a polyurethane resin (PU) and an unsaturated polyester resin was studied. A differential scanning calorimeter (DSC) was used to monitor the polymerization course. It was found that increasing the polyester content in a PU-polyester SIN enhanced the polymerization of PU due to the "solvent effect" of polyester. On the other hand, increasing the PU content in the SIN retarded the polymerization of polyester due to the "cage effect" of PU. Polymerization sequence of the SIN could be controlled by employing different initiators for polyester reaction. The degree of crosslinking in each SIN component had a significant effect on the dynamics of the SIN formation and on the limiting conversion of the polyester reaction.

Interpenetrating polymer networks of polyurethane and unsaturated polyester were prepared by reaction injection molding (RIM) and transfer molding. The structures of the molded samples were analyzed by electron microscopy and dynamic mechanical analysis. It was found that polymer morphology and dynamic mechanical properties depend strongly on the molding temperature, reaction rate and reaction sequence. Simplified structure models based on Takayanagi's model and sample morphology can predict the storage modulus reasonably well but not the tans.

SynopsisA series of polyurethane-polyester simultaneous interpenetrating network (SIN) samples were prepared by a laboratory-scale transfer mold. The effect of compound composition and molding conditions on the tensile properties and crystallinity of molded parts was examined by using an Instron tensile tester and a Perkin-Elmer differential scanning calorimeter (DSC). It was found that incomplete polymerization resulted in a poor tensile strength of 80°C-molded SIN. Postcure treatment and higher molding temperature increased the tensile strength of SIN by improving their limiting conversion and possibly the morphology. Results indicated that postcure was more efficient than molding at higher temperature for SIN samples with high polyurethane content. On the other hand, for SIN with higher polyester content, a high molding temperature resulted in better mechanical properties than postcuring the low-temperature molded samples. Both reaction sequence and cross-linking nature of the constituent polymers had a profound effect on the tensile properties of SIN.