As for CO2/CHO ROCOP, we observe an improvement in overall catalyst performance when moving to heavier alkali metals. While LCr shows a low TOF of < 5 h -1 and polymer selectivity of 12%, LCr Na exhibits an overall improved performance (TOF = 11 ± 2 h -1 , 61% polymer selectivity). The heavier alkali metals in LCr K/Rb/Cs all show a good polymer selectivity of 76% with improving linkage selectivity for the unscrambled OSS link when moving from K (37%) to Rb (53%) to Cs (58%). With regards to the catalyst rates, the maximum activities for LCr K/Rb/Cs (TOF = 67 -144 h -1 ) all exceed those of LCr and LCr Na . For LCr K and LCr Cs we observe an initiation period during which solubilization of the catalyst occurs. Nevertheless, one can clearly say that, as for CO2/CHO ROCOP, the heavier alkali metals K, Rb and Cs show improved performances in terms of both activity and selectivity over their lighter analogues Li and Na in the series of complexes LCr AM . Hence the order in catalyst performances exhibits clear parallels across ROCOPs. The copolymerisations yield materials with molecular weights (Mn = 5.42 -15.57 kDa) increasing with monomer conversions and somewhat broader molecular weight distributions (Đ = 1.29-1.67) than for CO2/CHO ROCOP.