The radical polymerizations of 1‐phthalimido‐1,3‐butadiene (1‐PB) and 1‐succinimido‐1,3‐butadiene (1‐SB) were carried out in bulk and in solution. The polymers obtained had reduced viscosities in the ranges of 1.0 –4.0 (1‐PB) and 0.2–0.6 (1‐SB). Both polymers had a similar softening point of 190–200°C. The radical polymerization of 1‐phthalimido‐1,3‐butadiene clearly showed a tendency to give crosslinked polymer. Steric arguments about these polymer structures as a result of the infrared and ozonolysis data led to the conclusion that these polymers contained approximately 20% of the 3,4 form but no 1,2 configuration, and, therefore, that the 1,4 addition was preferred.