But while polyurethanes are made up of several different urethane compounds, there are many more differences between polyurethanes and urethanes. Although the main difference is the compounds (polyurethane is basically a chain of urethane organic compounds, and urethane has a main functional group of compounds). Acrylic urethane differs from polyurethane in several noteworthy ways. For one thing, polyurethane chips and stains less easily than acrylic urethane.
Compel, impel agree in the idea of using physical or other force to cause something to be done. Compel means to constrain someone, in some way, to yield or to do what one wishes: to compel a recalcitrant debtor to pay; Fate compels us to face danger and trouble. Impel may mean literally to push forward, but is usually applied figuratively, meaning to provide a strong motive or incentive toward a certain end: Wind impels a ship.
Estoppel in English law. Estoppel in English law is a doctrine that may be used in certain situations to prevent a person from relying upon certain rights, or upon a set of facts (e.g. words said or actions performed) which is different from an earlier set of facts.