KINETICS AND PHASE SEGREGATION STUDIES ON THE RIM POLYMERIZATION OF URETHANE ELASTOMERS (POLYURETHANE).

摘要

Polyurethane elastomers are heterogeneous copolymers consisting of a soft, deformable phase and a hard, glassy or semicrystalline phase. In reaction injection molding, RIM, these materials are formed by a rapid, in-situ polymerization. This work analyzes the relationship between processing and polymerization conditions and structure-property relations.;Fourier transform infrared methods are used to monitor simultaneously extent of reaction and formation of interurethane hydrogen bonds leading to hard phase formation. In slow, isothermal systems, urethane associations and phase separation occur, creating a heterogeneous structure that affects completion of the reaction. The results are compared to those of previous investigations.;Phase separation and morphology of polyether based RIM polyurethanes have been studied by dynamic mechanical analysis, differential scanning calorimetry, wide angle x-ray scattering, attenuated total reflectance infrared and gel permeation chromatography. At low polymerization rates, phase separation occurs during the reaction. The final polymer has a well defined phase separated structure, poor phase connectivity, low molecular weight and low tensile properties. Rapid polymerizations lead to good domain connectivity, high molecular weight and tensile properties. Phase separation occurs during cooling of the molded part. Modulus temperature sensitivity is high due to incomplete phase separation and broad interphase boundaries. Phase separation can be improved by higher polyether molecular weight. Strong hard segment interactions are important in domain formation. In glycol extended polyurethanes, the interactions generally result from hard segment crystallizability. Amorphous polyurethanes tend to be compatible and do not yield good elastomers. In diamine extended polymers, interurea hydrogen bonding and rigid aromatic groups are major sources of interaction even in amorphous systems.;Adiabatic reactor methods are used to study bulk kinetics. Methods for parameter estimation are developed. The adiabatic mole balance is analyzed for an n-th order model to establish criteria for reaction acceleration due to exothermic effects. It also provides rapid methods to get kinetic parameters in simple models. A minimum activation energy is required for auto-acceleration to occur. Glycol extended systems have high activation energies and auto-acceleration takes place. Diamine extended systems have low activation energies; the maximum rate occurs at the start of the reaction.