here is what i found:
urethane is ethyl carbamate (C3H7NO2)(Carbon 3, Hydrogen 7, Nitrogen 1, Oxygen 2) and polyurethane is any polymer consisting of a chain of organic units joined by urethane (carbamate) links. Polyurethane polymers are formed through step-growth polymerization(Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers.) by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst.
That is polyurethane. Still working on reactive resin.
If that made your head hurt then be warned about this.
Synthetic resins are materials with similar properties to natural resins—viscous liquids capable of hardening. They are typically manufactured by esterification or soaping of organic compounds
. The classic variety is epoxy resin, manufactured through polymerization-polyaddition or polycondensation reactions, used as a thermoset polymer for adhesives and composites. Epoxy resin is two times stronger than concrete, seamless and waterproof. Accordingly, it has been mainly in use for industrial flooring purposes since the 1960s. Since 2000, however, epoxy and polyurethane resins are used in interiors as well, mainly in Western Europe.
One more category, which constitutes 75% of resins used, is unsaturated polyester resin. Ion exchange resin is another important class with application in water purification and catalysis of organic reactions. See also AT-10 resin, melamine resin. Another synthetic polymer is also sometimes called by the same suffix, acetal resin. By contrast with the other synthetics, however, it has a simple chain structure with the repeat unit of form -[CH2O]-.
So you see this is very complex stuff. I knew about 70% of what they said from Chemistry and Animal Life Science.