A thermally stable and transparent copolymer (PAED) composed of N-allylmaleimide, N-(2-ethylhexyl)maleimide, and diisobutylene as the repeating units was produced by radical copolymerization in the presence of an azo initiator in chloroform at 60 degrees C. The thiol-ene reaction between the allyl groups included in the side chain of PAED and the mercapto groups (SH) included in a random-type SH-modified silsesquioxane (SQ) as the crosslinker provided PAED-SQ hybrid materials upon heating. The reaction process for this thermal curing was monitored from the intensity changes of characteristic peaks by IR spectroscopy as well as the gravimetric determination of the isolated insoluble fractions. The thermal, optical, and mechanical properties of the hybrids were investigated. The onset and maximum decomposition temperatures were 322-369 degrees C and 399-431 degrees C, respectively. The weight residue at 800 degrees C was 16-40 wt%, which depended on the amount of the SQ content in the feed. These organic-inorganic hybrid materials were highly transparent and exhibited refractive index of 1.522-1.524 and Abbe number of 40.0-45.8. The tensile test and dynamic mechanical analyses were also carried out to investigate the mechanical properties and the network structures of the hybrids. The addition of triallylisocyanurate (TAIC) to the curing system efficiently improved the conversion of the allyl and SH, leading to the more dense network structure and the higher strength and hardness of the cured hybrids. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2294-2302