AbstractFumaric acid derivatives, dialkyl fumarates, alkyl N,N‐diethylfumaramates, and N,N,N′,N′‐tetraalkylfumaramides with bulky substituents were homopolymerized in the presence of a radical initiator to give high molecular weight and less‐ or non‐flexible substituted polymethylenes. Dialkyl maleates were also homopolymerized by preceding isomerization to the respective dialkyl fumarates in the presence of both an azo initiator and morpholine (isomerization catalyst). N‐Substituted maleimides underwent homopolymerization to give high molecular weight polymers, which have high thermal stability. These polymers were characterized as a new rigid polymer. Polymerization reactivities of the monomers and some properties of the resulting polymers are described