Sure seal

Waxy potato starch (>95% amylopectin, molecular weight in the range 10⁷–10⁹ Da and roughly 5% of α (1–6) branching points) was kindly donated by Avebe (Veendam, The Netherlands) and dried under vacuum at 60 °C for 48 h before use. Lithium chloride was purchased from Sigma-Aldrich and dried under vacuum at 80 °C for 24 h before use. Anhydrous N,N-dimethylacetamide (DMAc) was purchased from Sigma-Aldrich in Sure/Seal™ (Steinheim, Germany). 2-bromopropionyl bromide (BpB), formaldehyde solution (37%), and formic acid (>95%) were purchased from Sigma-Aldrich and used as received. Tris(2-aminoethyl)amine (Tren) was purchased from Tokyo Chemical Industry Co., Ltd. (TCI, Tokyo, Japan) and used as received. Tris[2-(dimethylamino)ethyl]amine (Me₆Tren) was synthesized following the procedures reported [33 ]. N-IsopropylAcrylamide (NIPAM, stabilized with 4-Methoxyphenol (MEHQ)) was purchased from TCI and recrystallized from acetone to remove the inhibitor. Acrylamide (AM) was purchased from Sigma-Aldrich and used as received. Copper powder (<75 μm) was purchased from Sigma-Aldrich and stored under an N₂ atmosphere.

All commercial reagents were purchased from Sigma-Aldrich, Alfa Aesar, Apollo Scientific, or Fluorochem and of the highest available purity. Anhydrous solvents were purchased from Acros (AcroSeal) or Sigma-Aldrich (SureSeal) and were stored under nitrogen. Proton nuclear magnetic resonance spectra were recorded at 500 MHz on a Varian VNMRS 500 MHz spectrometer, at 30°C. Carbon Nuclear Magnetic Resonance spectra were recorded at 125 MHz on a Varian 500 MHz spectrometer. LCMS data were recorded on a Waters 2695 HPLC using a Waters 2487 UV detector and a Thermo LCQ ESI-MS. Samples were eluted through a Phenomenex Lunar 3μ C18 50 mm × 4.6 mm column, using water and acetonitrile acidified with 0.1% formic acid at 1 ml/min and detected at 254 nm. The gradient employed was a 10 min. method of 5-95% MeCN. Mass Spectra (HRMS) were recorded at the University of Sussex Mass Spectrometry Centre on a high-resolution Orbitrap-XL instrument (Thermofisher). All experiments were carried out under an inert atmosphere of N₂ unless otherwise stated.