sentences:  The two men each filed substantively identical patents on the polymer at the same time.Because diapers are a low-margin product, it was deemed economically unfeasible to put Harmon and Harper's idea into mass production while the polymer was still under their patent protection.After the patent expired in the mid-1980s, however, manufacturers began to introduce "superabsorbent" disposable diapers, made with the polymers in place of excess paper in the diaper's core.