This paper presents a novel high-throughput approach to measure copolymerization reactivity ratios from a single experiment using high-speed real-time Fourier transform infrared (FTIR) monitoring of the isobutylene/isoprene (IB/IP) system initiated by 2-chloro-2,4,4-trimethyl-pentane (TMPCl)/TiCl4 in hexane/methyl chloride (Hx/MeCl) 60:40 v/v solvent at -80 degreesC. Traditional polymer analysis is severely limited in this system, which is riddled by side reactions. The reactivity ratios calculated by linear (Mayo-Lewis and Kelen-Tudos) methods and by a nonlinear least square (NLLS) method (van Herk algorithm) showed good agreement with r(1) = 1.32 and r(2) = 0.74 calculated using Mayr's nucleophilicity scale. Combination of the Kelen-Tudos and NLLS methods yielded r(1) = 1.17 +/-0.01 and r(2) = 0.99 +/- 0.02. These values agree well with those reported by Thaler et al. but disagree with most reported data. (C) 2004 Wiley Periodicals, Inc.