The Structur3d crew made a extensive attempts to 3d print with multi par polyurethane resin. They used custom print heads with mixed results. Mos tof the parts failed, but they are slowly moving towards success. If you want to experiment and see several techniques do check out their research.
Very detailed page with step-by-step process, extruder technology and g-code examples:
http://www.structur3d.io/blog/2015/12/3/3d-printing-with-polyurethane
Here is the video of the process: