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 <Mn <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/MADLX. 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.