Caprolactone cl

Caprolactone (CL, Sigma Aldrich, ST. Louis, MO, USA) was distilled before use. Polyglyerol adipate (PGA) was synthesized and purified as previously reported [34 (link)]. Tetrahydrofuran (THF, Sigma Aldrich) was dehydrated on CaSO₄. Tin 2-ethylexanoate (Sigma Aldrich), methanol (Sigma Aldrich), hexane (Sigma Aldrich) and usnic acid (Sigma Aldrich) were used without further purification.

Toluene, diethyl ether and tetrahydrofuran (THF) were refluxed with Na/benzophenone/dibenzo-18-crown-6 and distilled prior to use. Dichloromethane was refluxed over CaH₂ prior to use.
Acetic acid (Acros, ≥99.9%) was used as purchased. Poly(ethylene glycol) methyl ether (average M_n 550 Da, Sigma-Aldrich, St. Louis, MO, USA, 97%) was dried over 4 Å molecular sieves overnight prior to use. Poly(ethylene glycol) methyl ethers (average M_n 2000 Da, 5000 Da, Sigma-Aldrich, St. Louis, MO, USA, 97%) were used as purchased. (S,S)-3,6-Dimethyl-1,4-dioxane-2,5-dione (L-LA) (Sigma-Aldrich, St. Louis, MO, USA, 99%) was purified by recrystallization from dry toluene and subsequent sublimation and stored over P₂O₅. Caprolactone (CL) (Sigma-Aldrich, St. Louis, MO, USA, 97%) was distilled over CaH₂ prior to use.
[(BHT)Mg(OBn)(THF)]₂ (BHT = 2,6-di-tret-butyl-4-methylphenoxy, Bn = PhCH₂—), Mg1 [26 (link)], [(BHT)Mg(n-Bu)(THF)₂], Mg2 [27 (link)], methyl ethylene phosphate (MeOEP) [28 (link)] were prepared according to previously described methods.
CDCl₃ (Cambridge Isotope Laboratories, Inc., Tewksbury, MA, USA, D 99.8%) was used as purchased. The ¹H NMR spectra were recorded on a Bruker AVANCE 400 spectrometer (400 MHz) at 20 °C.