A combination of Monte Carlo simulation and gel content experiments was used to study the molecular structural evolution of two randomly crosslinked systems: ethylene vinyl acetate copolymer and metallocene polyolefin elastomer in the presence of a triallyl cyanurate polyfunctional monomer (PFM). The molecular weight distributions, crosslinking density and PFM density evolutions are simulated. There exist gaps in the crosslinking density and the bonded PFM density, between the gel and the sol fractions. The density gaps widen as the crosslinking reaction proceeds. Towards the end of the reaction, the gel crosslinking density increases at a rate higher than that for the gel PFM density. The crosslinking level for the PFM molecules in the gel fraction is much higher than that in the sol fraction. The evolved structures for the two polymer systems during the reaction are also discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.