Multicomponent cyclopolymerization (MCCP) based on isocyanides, among the tremendous synthetic methodologies, is a powerful tool for the preparation of functional heterocyclic polymers like poly(maleimide)s (PMDs), which should be further developed. In this work, an atom-economic and catalyst-free MCCP of activated alkynes, diisocyanides and diisocyanates was fully explored. The PMDs with high weight-average molecular weights (Mw up to 29 000) were facilely produced in satisfactory yields (up to 85%). The resultant polymers showed excellent solubility, high thermal stability, and good film-forming ability, and their thin films possessed high refraction indices (RI) in a range of 1.613 to 1.708 at 632.8 nm. Therefore, this work not only supplements the isocyanide-based multicomponent cyclopolymerizations but also enriches the family of polymerization reactions based on triple-bond building blocks.