Cure Conditions for Isocyanurate Polymers

Abstract

Structural RIM (MM/RIM) Composites are materials for use by automotive as well as industrial, agricultural, marine and leisure industries. Most often these composites are pictured as having sheet form because the re inforcement is made this way. Normal thicknesses are 0.100-0.125 inches; however, parts with different thicknesses may be required. For parts thicker than 0.125 inches Spectrim* MM composites based on polyisocyanurates are ideal because they do not scorch and parts up to 6-7 inches thick have been made which are well cured. To make parts thinner than 0.125 inches both ade quate wet-out of the glass reinforcement and cure of the polymer must be achieved. Because these polymers cure from the heat evolved in the reaction, cure is a function of the volume percent polymer contained in the mold. Thin parts have been found to have the same mechanical properties as thicker parts, but the cure is not complete as shown by the tendency of parts to be overly flexi ble on demold or to have poor green strength. It has been shown that the glass transition temperature, as determined by DMTA, is diagnostic for cure. Those parts which have too low a glass transition temperature require postcure. It has also been found that the state of cure is related to the maximum exotherm obtained during reaction and the duration of that exotherm. Thus, bulk polymerizations, in which the thickness is 2-5 inches, have exotherms which can exceed 400 °F and remain above 350 °F for about an hour. By contrast, thin parts may have exotherms which are not higher than the mold temperature.