IN-MOLD RIM KINETICS VIA MIDINFRARED FIBER OPTIC FT-IR

The relationship between the basic chemical reactions and morphology development in polyurethane polymers has been studied extensively. Interactions, such as hydrogen bonding, phase separation and chemical crosslinking, play a major role in the matrix formation of the polymer and have a pronounced effect on its processability and ultimate physical and mechanical properties. These interactions are, to a very large degree, controlled by the stoichiometry, relative reaction rates, inherent solubilities and chemical composition of the starting components, as well as the mixing and metering conditions. A variety of techniques have been used to study the final polymer; very few are adaptable for the study of the dynamics of the reaction injection molding (RIM) process. We are refining a fiber optic-based infrared technique which allows the researcher to study the in-mold conversion and cure of a RIM polymer without significant alteration of the mold cavity. This technique also allows for facile study of the postcure process. Using this technique, we have obtained infrared spectra of a reacting RIM polymer, in the mold cavity, every 0.5-1 second. Chemical reaction rates and morphology development have been evaluated using computer-assisted spectral analysis procedures to simultaneously monitor both isocyanate disappearance and the evolution of a variety of morphological features. Quantitation of the various products versus time is obtained via curve fitting and deconvolution routines. The resultant information provides a strong basic understanding of in-mold curt, green strength, ''post blow'' and reagent diffusion. Application of the technique has been proven in a wide variety of RIM and SRIM systems. In-mold evaluations of conventional unfilled polyurethane, polyurea and isocyanurate formulations will be discussed.