Moving to different sulfur loadings (Table , run #2 -#5) showed that polymer and sequence selectivity positively correlate with the amount of supplied S8 in the starting monomer feed. Very high sequence selectivity of >98% and polymer selectivity of >90% could be achieved. Note that the lithium-alkoxide catalysed ROCOP of CS2/PO in the absence of S8 gave a decreased polymer selectivity of ca. 60%. This is particularly dramatic at higher reaction temperature of 80 °C, for which ROTERP (run #6) gave 90% polymer selectivity while ROCOP of CS2/PO (run #7) produced no copolymer but only cyclic dithiocarbonate. Evidently, supplying additional S8 is beneficial to improve polymer selectivity. Comparing the 1 H NMR spectra of the obtained copolymers showed that the tertiary CH resonances are always observed as two overlapping resonances centred around 5.64 and 5.72 ppm, and the latter becoming increasingly pronounced in copolymers obtained with higher initial S8 loading.