Lewis-acid catalyzed degradation of poly(isobutylene-co-isoprene) (butyl rubber) in the presence of an alkoxybenzene compound was studied as a new route toward low molecular weight multifunctional polyisobutylenes. Simultaneous cleavage and functionalization of butyl rubber was conducted at -70 degrees C and -40 degrees C under TiCl4 or AlCl3 catalysis in 60/40 hexane/methylene chloride cosolvents in the presence of (3-bromopropoxy)benzene (BPB) for various times up to 24 h. The butyl rubber (EXXON Butyl 365) possessed M-n=1.91 x 10(5) g/mol, PDI=1.66 (GPC/MALLS), and 2.30 mol % isoprene units (nearly exclusively trans-1,4). At -70 degrees C with TiCl4, molecular weight was reduced to various values within the range 7 to 11 x 10(3) g/mol depending on conditions; lower BPB concentration produced lower molecular weight. However, the ratio of isobutylene repeat units to BPB units (IB/Q) remained constant at about 43:1, which is approximately the same as the ratio of isobutylene to isoprene repeat units (IB/IP) in the starting butyl rubber (42.5:1). At -40 degrees C with TiCl4, molecular weight was reduced to about 5 x 10(3) g/mol, and IB/Q was reduced below IB/IP, indicating nearly a difunctional telechelic structure. AlCl3 was a more active catalyst and produced results similar to TiCl4 at -40 degrees C, even when used at seven times lower concentration. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1991-1997