Precision polyurethane manufacture

A process for making a polyurethane, comprising:

• reacting reagents comprising a multifunctional isocyanate, a polyol and a chain extender, wherein the reagents are from separate sources and first contact one another when the reagents are intensively mixed by intimately mixing the reagents at a molecular level to form a uniform mixture prior to being introduced into an extruder, wherein said reagents are intensively mixed via a reactive injection technique, the intensive mixing occurs substantially instantaneously, the resultant mixture from said intensive mixing is substantially homogeneous immediately after mixing and the resultant mixture from said intensive mixing is fed directly into an extruder;
• and
• extruding the mixture into a mold to form a polyurethane having a predetermined stoichiometry distribution and thermal history,
• wherein the relative amount of the reagents to be intensively mixed is perturbed during the process prior to intensively mixing the reagents to change the relative amount of the reagents in the mixture, and the intensively mixing of the reagents is at a degree such that the predetermined stoichiometry distribution of the polyurethane is controlled by the perturbation.