Roshni suggests N,N-dimethylacetamide (DMAc) might be good to dissolve the MDI rather than chloroform, from paper: Xiang-Dong Sun and Chong Sook Paik Sung, Cure Characterization in Polyurethane and Model Urethane Reactions by an Intrinsic Fluorescence Technique, Macromolecules 1996, 29, 3198-3202.
DMAc now ordered.
Might be worth having a look at the newly formed glass substrates with PU from last time on an optical microscope and seeing if MDI crystals can be seen.
