## 3 Materials and Methods  
### General  
All the reactions were performed using standard Schlenk techniques under a dry argon atmosphere. Products were purified with flash chromatography on Merck silica gel (particle size 230-400 mesh, porosity 60 A).  
NMR spectra were recorded on a Bruker Avance II 400 (Bruker, Zurich, Switzerland, strength of the magnetic field is 9.4 T, operating frequencies are 400 MHz for \({}^{1}\)H and 100 MHz for \({}^{13}\)C) or Bruker Avance II 600 (Bruker, Zurich, Switzerland, strength of the magnetic field is 14.1 T, operating frequencies are 600 MHz for \({}^{1}\)H and 150 MHz for \({}^{13}\)C) spectrometers in CDCl\({}_{3}\) at 298 K. Chemical shiftsare expressed in parts per million with chloroform signals as internal reference (\(\delta\) = 7.26 ppm in \({}^{1}\)H and 77.16 ppm in \({}^{13}\)C-NMR). In case of polymer solutions, relaxation delay was increased to 10 s to optimize the accuracy of integration.  
Number-average molar mass (\(M_{\text{n}}\)) and dispersity 0 values of the polymer samples were determined by SEC. Analyses were conducted on a system composed of Waters 515 HPLC pump (Waters S.A.S., Saint-Quentin En Yvelines, France), Agilent 1260 Autosampler (Agilent Technologies France, Les Ulis, France), Varian ProStar 500 column valve module (Agilent Technologies France, Les Ulis, France), set of three Waters columns (Styragel Guard Column, 20 \(\upmu\)m, 4.6 mm \(\times\) 30 mm, Styragel HR3, 5 \(\upmu\)m, 7.8 mm \(\times\) 300 mm and Styragel HR4E, 5 \(\upmu\)m, 7.8 mm \(\times\) 300 mm) and Wyatt Optilab rEX differential refractive index detector (Wyatt Technology France, Toulouse, France) using tetrahydrofuran as an eluent at a flow rate of 1.0 mL min\({}^{-1}\) (35 \({}^{\circ}\)C). The column system was calibrated with PMMA standards (ranging from 1.120 to 138.600 kg mol\({}^{-1}\)) using the Landau-Kuhn-Mark-Houwink-Sakurada equation [38]. Prior to injection, samples were diluted to a concentration of 5 mg mL\({}^{-1}\) and filtered through 0.45 \(\upmu\)m Nylon syringe filters.  
Metal concentrations were measured using a Thermo Scientific iCAP 6000 Series inductively coupled plasma - optical emission spectrometer (ICP-OES, Thermo Fisher Scientific, Waltham, MA, USA) equipped with autosampler (ASx 260). Standard deviations (SD), limits of detection (LOD) and limits of quantification (LOQ) are listed in Table S1, calibration curves are depicted in Figures S6-S10.  
Aqueous solutions were analyzed with ICP-OES without additional sample treatment. Organic solutions were dried under reduced pressure, remaining solids were mixed with concentrated nitric acid (2 mL) in a glass vial and heated for 24 h at 100 \({}^{\circ}\)C. If sample was not completely digested, concentrated sulfuric acid (2 mL) was added and heating was continued at 120 \({}^{\circ}\)C for 24 h. Obtained solutions were cooled to room temperature and adjusted with 4% aqueous nitric acid to initial volume prior to ICP-OES analysis.  
Alkene terminated polyisobutylene (PIB, Glissopal\({}^{\circledR}\) 1000) was received as a gift from BASF and used as is. All other reagents and solvents were commercially supplied by Sigma Aldrich and used without further purification, unless otherwise stated.