P.A.T 1173 Photoinitiator 2-Hydroxyl-2-methylpropiophenone is a versatile, highly efficient, liquid photoinitiator used to initiate the photo-polymerisation of chemically unsaturated prepolymers - e.g. acrylates-in combination with mono or multifunctional monomers. 1173 is especially recommended when UV coatings are required to exhibit only minimal yellowing even after prolonged exposure to sunlight.