Graft block copolymers of propargyl methacrylate and vinyl acetate via a combination of RAFT/MADIX and click chemistry: Reaction analysis

Propargyl methacrylate with its acetylene function protected with a silyl group is polymerized via the reversible addition fragmentation chain transfer (RAFT) process, using cyanoisopropyl dithiobenzoate (CPDB) as RAFT agent, and subsequently deprotected. to afford a polymer backbone where each repeated unit is decorated with an acetylene functionality (1000 < M-n < 13,600 g mol(-1), 1.07 < PDI < 1.29). In parallel, an azide functionalized xanthate (ethoxythiocarbonylsulfanyl-acetic acid 3-azido-propyl ester) was employed to prepare narrow polydisperse poly(vinyl acetate) (M-n = 850 g mol(-1), PDI = 1.20). The two polymers are conjugated by Huisgen 1,3-dipolar cycloaddition to afford narrow polydisperse comb polymer (1.12 < PDI 1.18, 3400 < Mn < 12,500 g mol(-1), based on linear polystyrene calibration, 4500 < M-n(theo) < 15,600 g mol(-1)). The study places special emphasis on following the copper catalyzed 1,3-dipolar cycloaddition via Fourier Transform Infrared Spectroscopy (FTIR) as well as via on-line UV-Vis photospectrometry on several model compounds, i.e. the nonmonomer inserted azido-xanthate RAFT/MADIX agent as well as a 2-propargyl-2-bromopropionate and 3-azidopropyl-2-bromopropionate model compounds. A suitable absorption band in the VIS at 666 nm (tentatively assigned to a charge transfer complex between copper(I) and the forming triazole moieties) is identified as a promising sensor for following the click reaction kinetics, thus allowing for the rapid assessment of reaction completion in an on-line fashion. (c) 2007 Wiley Periodicals, Inc.