We report the synthesis of high-molecular-weight linear polyisobutylenes (PIBs) and PIB networks from low-molecular-weight PIB by thiol-ene click chemistry. Thus, liquid allyl-telechelic PIB was reacted with small di- and tri-thiols, and the thiolated intermediates chain-extended by UV- or thermally induced free radical initiation to linear and crosslinked products. PIB networks were also prepared by crosslinking SH-telechelic PIB with a small triallyl compound. Linear products were characterized by H-1 NMR spectroscopy and GPC, and networks by FTIR spectroscopy, extractables, swelling, and permanent set. The effect of reaction conditions (nature of thiol chain extender, concentration of photo- and thermal initiators, UV radiation time, and reagent concentrations) on chain extension and crosslinking was investigated. Under well-defined conditions high-molecular-weight PIBs and tight PIB networks were prepared. Thiol-ene click chemistry provides novel thiolated PIB derivatives and is a useful strategy for the convenient preparation of high-molecular-weight rubbery PIBs and tight PIB networks from low-molecular-weight PIB precursors. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019