Bill Tindall, E.Tn.
To get the crosslinking to go at typical temperatures requires a highly reactive substance. Any chemical that can cross link a resin will cross link most every component of a cell.
Toluene is benign. It is a common industrial solvent because its primary hazard is flammability. Fretting over toluene in the company of an isocyanate is like worrying you might trip going down the stairs in a house afire.