Triethyl orthoformate

DHBA (3,4-Dihydroxybenzoic acid), 1,1′-carbonyldiimidazole (CDI), thionyl chloride (SOCl₂), triethyl orthoformate (TEOF), resin Amberlyst 15, polycaprolactone diol with molecular weight of 2037 (PCL-2000), 1,4-butanediol (BD), ε-caprolactone (ε-CL), tin(II) 2-ethylhexanoate (Sn(Oct)₂), N,N-dimethyl-acetamide (DMAc), and 1,6-diisocyanatohexane (HDI) were purchased from Sigma-Aldrich (Madrid, Spain). The diisocyanate product was freshly distilled at low pressure before use, and the rest of the products were used as received. AMPD (2-Amino-2-methyl-1,3-propanediol) and N,N-diethanolamine (DEA) were purchased from Merck (Madrid, Spain) and used as received.

All experiments were carried out in an atmosphere of dry argon and flasks were flame dried. Solvents were dried by usual methods (diphenyl ether, diethyl ether and THF over benzophenone ketyl, CHCl₃ and CH₂Cl₂ over P₄O₁₀, hexane over sodium-potassium alloy) and distilled. Chromatographic purification was carried out on silica gel 60 (0.15–0.3 mm, Macherey-Nagel GmbH & Co. KG, Düren, Germany). Sodium hydride (dry, 95%), trimethyl orthoformate, triethyl orthoformate, triethyl orthoacetate, trimethyl orthoacetate, 1,10-phenanthroline (4n), 1,10-phenanthrolin-5-amine (5l), 9H-carbazole, pyrrolidine, 10H-phenothiazine, Meldrum’s acid, benzene-1,2-diamine, 4-fluorobenzene-1,2-diamine, 4-chlorobenzene-1,2-diamine, 4-bromobenzene-1,2-diamine, 4-methylbenzene-1,2-diamine, 3,4-diaminobenzonitrile and 3,4-diaminobenzoic acid were purchased from Sigma–Aldrich (Poznan, Poland), and were used without further purification.