AbstractHyperbranched polymaleimide can be readily obtained by copolymerization of allyl maleimide and propyl maleimide. A hyperbranched polymaleimide was obtained in a yield of 56 wt % in 3 h at 50°C, whose weight average molecular mass and polydispersity index were measured by size‐exclusion chromatography to be 59,000 and 4.1, respectively. TGA showed a one‐step mass loss process in the decomposition of the hyperbranched polymaleimide. The dominant pyrolysis mechanism was revealed by gas chromatography/mass spectrometry to be depolymerization. The major pyrolysates of the hyperbranched polymaleimide were allyl maleimide, propyl succinimide, and other volatile monomeric units. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1848–1852, 2006