The monomer solution was prepared in a dried Schlenk flask under an inert atmosphere by dissolving Sar-NCA (1.47 g 13.03 mmol; 96.5 eq.) and 4MTPPC (0.034 g 0.135 mmol, 1.0 eq) in 5 mL of PhCN and 3 mL of MeCN. The reaction solution was stirred under an inert and dry atmosphere at room temperature for 24 h. In the first 2.0 h, a vial was opened to reduce CO2.