In summary, the study shows that rigid urethane foams made from ethers
have higher compressive strengths, from -320°F up to about +300°F, than
comparable ester foams. Presumably, this difference in load-bearing
properties can be attributed to stronger secondary bonding in ethers since
the primary bonding in both foams was equivalent. In comparing the
stability of these foams, from the standpoint of oxidative stability, thermal
decomposition, and thermalmechanical behavior, the ester foams are more
thermally stable than the ether foams.