Reaction kinetics of simultaneous interpenetrating polymer networks (SIN) composed of polyurethane (PU) and unsaturated polyester (UPE) was studied for the application of reaction injection molding (RIM) process. A differential scanning calorimeter (DSC) was used to monitor the polymerization reaction. The polyurethane network was prepared by reacting 4,4'-diphenyl methane diisocyanate(MDI), poly (tetramethylene ether glycol) (PTMG) and trimethyol propane (TMP) using cobalt naphthenate as the acatalyst, and the unsaturated polyester resin composed of phthalic anhydride, propylene glycol and fumaric acid was crosslinked with styrene in the presence of methyl ethyl ketone and cobalt naphthenate.
The reaction kinetics during the IPN formation was very complicated since the reaction of the each component polymer affected each other in spite of the different reaction mechanisms. As the amount of PU in the simultaneous IPN (SIN) was increased, the polymerization of unsaturated polyester was retarded due to the cage effect of the polyurethane network which restricted the diffusion of the styrene monomer. The final conversion of the unsaturated polyester reaction decreased in SIN. However, the reaction rate of the unsaturated polyester was accelerated due to the catalytic effect of the isocyanate group on the initiator decomposition of the unsaturated polyester. On the other hand, the polyurethane reaction rate in SIN was not affected significantly by the reactants of unsaturated polyester.
The mechanical properties were measured with variations in composition and crosslink density of the component polymer. From dynamic mechanical analysis (DMA), it was found that the component polymers were incompatible over the wide range of composition. Therefore, phase separation occurred between PU and UPE. When the content of PU was 40%, tensile strength showed a minimum value because PU was very incompatible with the unsaturated polyester. However when he content was above 60%, the tensile strength of PU was improved greatly by UPE. Tensile modules decreased and the elongation and impact strength increased as the polyurethane content was increased. When the polyurethane content was low (about 10%), the significant improvement of the impact strength of UPE due to the domain formation of PU rubbery phase from the partial phase separation of the two component polymers was observed. When crosslinking density was increased, the compatibility was enhanced and the mechanical properties were improved considerably.
