In terms of side reactions, a loss of linkage (exemplified for LCr Rb from 53 to 16%) and polymer selectivity (from 76 to 35%) is observed when increasing the reaction temperature from 60 to 100°C (Table , run #10 and #12). Looking at the combined results presented in Table it becomes clear that polymer and OSS linkage selectivity correlate suggesting that dt-c5c generation and O/S scrambling occur through mechanistically related processes. In CO2/CHO ROCOP it is well established that c5c formation occurs via back-biting of an alkoxide chain end into the adjacent carbonate link. Therefore, we presume that O/S scrambling occurs from side reactions of loosely coordinated alkoxide chain ends and related hypotheses have been formulated previously which remain to be confirmed experimentally and computationally. Bearing this hypothesis in mind we turned towards elucidating the CS2/CHO ROCOP side-reaction mechanism. To experimentally survey the intermediates and side reactions (ESI Section S5), we synthesized a model alkoxide A M choosing simple rubidium cyclohexyloxide RbOCy, to avoid the paramagnetism of Cr. Addition of 5 eq. CS2 at ambient temperature in THF (Figure ) leads to quantitative formation of the related rubidium dithiocarbonate RbSC(=S)OCy DTC M ( (C q =S) = 229.9 ppm). Attempting to regenerate an alkoxide we added 1 eq. of CHO to DTC M in d -DMSO at ambient temperature but did not observe any CHO ringopening, further supporting epoxide insertion to be the rate determining step of CS2/CHO ROCOP. Heating the reaction mixture at 100°C for 30 min results in CHO ring opening forming a complex reaction mixture instead of the expected dithiocarbonate appended alkoxide A M1 (Figure ). NMR and IR analysis reveals the formation of the rubidium monothiocarbonate RbSC(=O)OCy MTC M ((C q =O) = 183.0 ppm and ṽ(C=O) = 1587 cm -1 ) as well as poly(cyclohexene sulfide) alongside the precipitation of the rubidium carbonate RbOC(=O)OCy C M (ṽ(C=O) = 1657 cm -1 ). Isolated MTC M (vide infra) likewise only reacts with CHO upon heating to 100 °C in d6-DMSO with precipitation of C M and poly(cyclohexene sulfide) formation. This indicates that the generation heterocarbonates other than DTC and OSS occurs rapidly following CHO intertion which leads to oxygen enriched carbonates and deployment of the excess sulfur in thiirane byproducts. We believe nucleophilic attack of the metal alkoxide into the adjacent dithiocarbonate link in A M1 to be the entry point to this process. To confirm this hypothesis, we reacted A M with the dithiocarbonate dt-c5c and the monothiocarbonate mt-c5c in THF at ambient temperature (Figure ). Reacting A M with dt-c5c results in instant discolouration and precipitation of a colourless solid which we could identify as MTC M . Additionally, 1 H NMR analysis of the supernatant solution unambiguously reveals the formation of CHS. Likewise reacting A M with mt-c5c leads to precipitation of C M and thiirane generation. In reference to previous hypotheses by Werner and coworkers, we propose a reaction pathway (Figure ) in which the metal alkoxide attack into organic (di)thiocarbonates generates a tetrahedral intermediate I, which collapses into an oxygen enriched organic (thio)carbonate appended metal thiolate T that can eliminate thiirane to release MTC M or C M . This substantiates the hypothesis that O/S scrambling occurs via alkoxide originated backbiting pathways and also explains thiirane by-products observed during CS2/CHO ROCOP. Knowing the origin of O/S scrambling, one can formulate a CS2/CHO propagation mechanism explaining the product distribution. Initially in the primary propagation cycle (Figure ) alternating CS2 insertion starting from the alkoxide intermediate A gives DTC which then inserts CHO generating OSS links sitting adjacent to metal alkoxide chainends A . Backbiting generates a tetrahedral intermediate I that in one instance can eliminate dt-c5c to regenerate A. Alternatively I can rearrange into a metal thiolate chain-end T generating an OSO link and resulting in O/S scrambling between the chain-end and the adjacent heterocarbonate link. From T thiirane elimination generates a metal monothiocarbonate chain-end MTC that then continues to propagate. In order to assess the energetic feasibility of these reaction pathways we again turned to DFT. As displayed in Figure , initial backbiting from A 1 takes place via TS3 (+21.7 kcal mol -1 ) to form I (+14.0 kcal mol -1 ). From I release of dt-c5c takes place initially via rearrangement of the ligated heterocycle to form I' (+18.3 kcal mol -1 ), and subsequent C-O cleavage via TS4 (+21.1 kcal mol - 1 ) to form I(dt-c5c) (-1.2 kcal mol -1 ). Alternatively, from I, a series of rearrangements of the ligated heterocyclic group (via TS5, I'' and TS6) ultimately yields I''' (+3.7 kcal mol -1 ). Ring-opening can then take place from this species via TS7 (+18.7 kcal mol - 1 ) to form T (+8.0 kcal mol -1 ) to finalize the O/S scrambling process, followed by rearrangement of the ring-opened chain to exergonically afford T' (-8.3 kcal mol -1 ). The calculations thus indicate that O/S exchange is kinetically accessible, where the largest energetic span of the process is 23.3 kcal mol -1 , and exergonic overall (ΔG from A 1 = -8.3 kcal mol -1 ). This indicates that O/S scrambling is thermodynamically driven owing to the more favourable accumulation of negative charge on S compared to O. From T', thiirane formation via C-O cleavage and concomitant transfer of the electrophilic C centre to the Cr-bound thiolate group via TS8 (+8.4 kcal mol -1 ) is identified to be kinetically accessible, with an overall activation barrier of +16.7 kcal mol -1 to form MTC(S) (-7.6 kcal mol -1 ). Onwards thiirane release is then characterized to form MTC (-21.0 kcal mol -1 ) which is structurally related to DTC and C (vide supra) and favours a bridged thiocarboxylate coligand. Therefore, the energetics of these side-processes are in agreement with the experiment identifying them as kinetically and thermodynamically viable and in competition with copolymerization. Having computationally verified the viability of the key events in O/S scrambling one can explain the formation of the other links with closely related reaction steps (Figure ). CHO insertion by MTC forms an OOS link appended metal-alkoxide chain-end A . A backbiting process alike the prior one through II leads again to O/S scrambling between the chain-end and the adjacent heterocarbonate link generating a metal-thiolate chain-end T and an all oxygen OOO link. Generation of all sulfur SSS links can be rationalised by CS2 insertion into metal thiolate chainends forming metal trithiocarbonate chain-ends TTC followed by propagation. As we have shown above (Figure ) that formal O to S substitution has little effects on the intermediate and transition state geometries we infer this is also the case of MTC and TTC so that metal-metal cooperativity is also maintained in these steps. Finally it should be noted that the scrambling process that have been formulated at the chain-end can likewise occur by attack of alkoxide chain ends into any heterocarbonate link of the chain which could at least partially explain the broaded (Ð > 1.3 -1.7) molecular weight distributions of the CS2 copolymers. Transmission (%) ṽ (cm -1 ) Owing to the mechanistic similarities between the CO2 and the CS2 ROCOP process we suspected their ring-opening terpolymerisation (ROTERP) to be feasible (ESI Section S6). Accordingly we performed CO2/CS2/CHO ROTERP at 100°C employing LCr Rb (1 eq. LCr Rb : 1000 eq. CHO : (500-3000) eq. CS2 under 4 bar CO2 pressure) and the results are summarized in Table . Under these conditions the terpolymerisation can be performed in screw cap glass vessels with tightly attached tubing as the applied overpressure increases the boiling point of the reaction mixture sufficiently which obviates the need for steel reactor set-ups. In all cases we observe successful terpolymer formation in good to excellent polymer yields of 53 -95% with respect to dt-c5c as the only cyclic carbonate by-product. We observe preferential formation of OOO linkages (64 -95%) with increasing proportions of sulfurated links when more CS2 is employed in the starting mixture. This suggests preferential carbon dioxide incorporation during ROCOP due to kinetically favoured CO2 over CS2 insertion by metal-alkoxide intermediate as predicted by our computational studies. NMR analysis of the terpolymers shows that all heterocarbonate links observed in CS2/CHO ROCOP, i.e. OOS, OSO, OSS and SSS, are incorporated in the terpolymer with OOS and SSS links being the most prominent (80 -90 %) ones irrespective of the starting feed ratio. Moving to lower temperatures (80 °C) or higher CO2 pressure (20 bar) results in no sulfur incorporation on the 1 H NMR, while higher temperatures (120 °C) only yield oligomeric products (Mn < 2kDa). Monitoring a ROTERP reaction by aliquot NMR analysis reveals that all links form in constant proportion throughout the ROTERP process supporting random as opposed to gradient terpolymerisation. The ROTERP methodology yields terpolymers with molecular weights Mn = 4.67 -12.65 kDa (Đ = 1.29-1.62) which formally constitute CO2 derived polycarbonates with a few randomly interspersed sulfur centres. Consequently, they are brittle materials with a Tg of 85.3 °C and a refractive index of 1.49 for Table run #2 which is very similar to the values for all oxygen variant with a Tg of 90.4 and a refractive index of 1.48 for Table run #11. However, we were intrigued to see how polycarbonate sulfuration affects the degradability of the material given that sulfur containing polymers are susceptible to oxidative and photolytic breakdown (ESI Section S7). Hence, we initially investigated oxidative disassembly of the respective CS2 or CO2/CHO copolymer (Table run #4 and #11). Immersion in aqueous H2O2 overnight leads to complete disintegration of the CS2/CHO copolymer with no polymeric products detectable by GPC. The initially highly hydrophobic and yellow polymer turns into colourless degradation products that homogenously disperse in the aqueous medium, indicating increasing hydrophilicity and loss of the yellow C=S chromophores during degradation. H NMR analysis of the degradation products shows the complete disappearance of resonance associated with C=S containing links, while C=O containing links remain intact. IR analysis of the decomposition products reveals emergence of bands at ca. ṽ = 1150 and 1250 cm -1 which are indicative of S=O from e.g. sulfone or sulfonic acid groups and our results therefore indicate degradation via oxidation of the sulfur centres. Accordingly, the all-oxygen CO2/CHO copolymer stays fully intact under the same conditions. Gratifyingly the CO2/CS2/CHO terpolymers (Table , run #1 and run #2) degrade into oligomeric products with Mn ⪅ 2 kg/mol. NMR analysis of the produced mixture reveals that the resonances associated with the OOO links of the terpolymer remain unaffected by the oxidation process while the resonances associated with the sulfurated links partially disappear and shift (Figure ), confirming that the sulfur containing links act as preinstalled oxidatively labile breaking points (Figure ). Next, we turned towards UV degradation of our materials (Table , run #4 and run #10). UV irradiation of the CS2/CHO copolymer in CDCl3 solution for 24 h leads to complete disintegration of the material with no polymeric products detectable by SEC. NMR analysis of the degradation products shows emergence of alkene resonances ( (  H) = 5.7 ppm;  (  C) = 127.5 ppm) indicating degradation via Chugaev elimination pathways. Accordingly, FTIR analysis of the reaction headspace reveals the formation of CS2 and COS. In contrast, the all-oxygen analogue CO2/CHO polycarbonate stays fully intact under the same conditions. However, the CO2/CS2/CHO terpolymers (Table , run #1 and run #2) degrade into oligomeric products with Mn ⪅ 2 kg/mol upon UV irradiation (Figure ). Our results hence show that the sulfur containing links also act predetermined photochemical breaking points in the otherwise robust polycarbonates. Sulfuration as little as ca. 1 out of 20 links (Table , run #1) lets the material access complementary degradation pathways.