Abstract: Reaction injection molded (RIM) or structural RIM (SRIM) resins having improved (prolonged) set times, that is, reduced reactivity, may be produced by the addition of an acid blocked amino acid salt catalyst as co-catalyst, or even as a sole catalyst. This permits large molds to be filled completely before cure. However, cure rates are not affected permitting high production rates. The physical properties of RIM and SRIM compositions do not suffer from the addition of these co-catalysts. The amino acid salts may have the formula: ##STR1## where R and R' are independently selected from the group consisting of hydrogen and alkyl having 1 to 12 carbon atoms; where the R" groups are independently alkylene groups having from 1 to 4 carbon atoms; where M is an alkali metal; and where x ranges from 1 to 4.