A polymer precursor containing an oxazolin-2-one ring is made by reacting (a) an amino-reactive group containing compound having at least two groups capable of entering into an addition or condensation reaction with primary or secondary aromatically-bound amino groups with (b) an aromatic amine having at least one primary or secondary aromatically-bound amino group and at least one condensed oxazolin-2-one ring. The reactants are used in quantities such that for each aromatically bound primary or secondary amino group there are from 0.95 to 5 groups present in the amino-reactive group containing compound which are capable of reacting with the amino group. These polymer precursors may be used to produce high molecular weight polymers useful in the production of solid molded products, adhesives, foam plastics and coatings.