Meaning
Low molecular weight byproducts of polyoxyalkylene hexamethylene diisocyanate reactions represent the chemically active fraction in uncured polyurethane precursors. These poah oligomers create localized variations in crosslinking density during the mould cycle. The presence of these chains influences the ultimate viscosity of the reacting monomer pool and dictates the kinetics of the final curing step.
Processing Impact
Heat accumulation in the tool promotes the accumulation of poah oligomers at the cavity interface. High concentrations cause surface tackiness or premature adhesion to the mould wall. The injection pressure required to fill the part increases when the concentration of these low-weight components rises beyond the design specification for the resin.
Quality Threshold
Material datasheets establish the maximum allowable concentration for poah oligomers to ensure repeatable mechanical properties across large production runs. Virgin material typically contains levels below the threshold of interference. Recycled batches often exhibit higher concentrations because the thermal history of regrind encourages chain scission and the subsequent formation of more small molecules.
Thermal Sensitivity
Cooling rates dictate how poah oligomers distribute throughout the cross section of a finished component. Rapid quenching traps these mobile species in the surface skin where the molecules interfere with secondary finishing operations such as painting or adhesive bonding. Slow cooling cycles allow the migration of these components toward the core, which prevents localized surface failure at the cost of potential internal density gradients.
