Interestingly, no crystallisation from solution is observed for these scrambled polymers which are obtained as amorphous semi-solids (vide infra for further discussion). It has been previously suggested that side-reactions originating from alkoxide intermediates are responsible for the scrambling process. Hence, we reacted preformed poly(dithiocarbonate) (100 eq. repeat unit, Table run #1) with LCrK (1 eq.) and OX (1000 eq.), conditions under which due to the absence of CS2 only alkoxide intermediates can exist, and indeed observed scrambling of the polymer (from 6% to 90% after 24h at 80ºC). Combined our results outlined in this paragraph indicate that LCrK supresses side reactions originating from decoordinated alkoxide chain ends via metalmetal cooperativity. Matching of the correct metals as well as ensuring cooperativity by fixing both active metals within the same ligand scaffold are vital to achieve high sequence selectivity in CS2/OX ROCOP. As depicted in Figure (c) we infer in reference to recent computational studies by Williams and co-workers on CO2/epoxide ROCOP that alkoxide based reactions originate from chromate centres while heteroallene activation occurs at the alkali metal. Considering that reaction step (i) represents the entry point to O/S scrambling pathways (ESI Section S10) in reference to Darensbourg and Werner it becomes clear that if both metals are not fixed within the same scaffold the intermolecular propagation pathway (i) has to compete with the intramolecular scrambling pathway (ii) and the same is the conceptually the case for other bicomponent catalysts. Heterobimetallic LCrK is hence inferred to lead to intermolecular propagation (i) and thereby avoid O/S scrambling. The circumstance we observe 99% polymer selectivity irrespective of the employed reaction conditions (Table ) or oxetane (Table ) is surprising considering reports concerning the all-oxygen counterpart, i.e. CO2/OX ROCOP. Here, cyclic trimethylenecarbonate by-products are formed due to establishing (de)polymerisation equilibria between poly(trimethylenecarbonate) and the cyclic six-membered carbonates. As this observation is most pronounced in geminally disubstituted derivatives due to the Thorpe-Ingold effect, we compared the relative energies of formation of the carbonate polymer carbonate P and the cyclic carbonate C from OX Me and CO2 as well as the alternating dithiocarbonate polymer P T and the cyclic dithiocarbonates C T from OX Me and CS2 on the B3LYP/cc-pVDZ level of theory (Figure (a1/2)) with periodic boundary conditions for P and P T (ESI Section S11), i.e. considering the energy of formation of one repeating unit in an infinite chain. As immediately apparent, CE2/OX Me coupling to either cyclic (E = -61 kJ/mol for E = O and -103 kJ/mol for E = S) or poly(dithio)carbonate (E = -116 kJ/mol for E = O and -148 kJ/mol for E = S) is more exergonic for CS2 than for CO2, a likely consequence of the decreased stability of a C=E bond versus two C-E bonds which are broken and formed the coupling process when moving from O to S. In both cases the polymers P or P T are more stable than the respective cyclic forms C or C T reflecting inter alia the release of ring-strain energy upon polymerisation. However, polymer stability is more pronounced in the all-oxygen case (Figure (a1), -55 kJ/mol moving from C to P) than in the sulfurated case (Figure (a2), -45 kJ/mol moving from C T to P T ) which is surprising given the near quantitative polymer selectivity of our CS2 ROCOP compared to previous CO2 ROCOPs (vide supra) giving cyclic carbonate by-products due to equilibrium limitations. Comparison of the bonding situation in the respective small molecules with the polymers (i.e. C with P and C T with P T ) shows near identical bonding orders in C and P as well as C T and P T . This suggests that not electronic changes, but rather different ring strain energies of C and C T are responsible for the differences in poly-versus cyclic (dithio)carbonate stability which we infer is due a greater tolerance towards bond-angle variation when moving down the periodic table. Combined, these results imply that the (de)polymerisation equilibrium of the P T ⇄C T copolymer must lie more on the cyclic (dithio)carbonate side then for the all-oxygen equilibrium P⇄C under identical conditions. In this respect Endo and co-workers reported that catalytic KO t Bu in THF reconstitutes equilibria states of isolated P, i.e. starting from 100% P at 0.45M in THF and 20 ºC resulted in 7% C and 93% P at equilibrium. Subjecting isolated the CS2/OX Me copolymer P T * (i.e. P T with 92% OSS and 8% OSO-alt-SSS links; Table , run #1) to analogous conditions results in >99% depolymerisation into ca. 95% C T and ca. 5% unidentified by-products and this confirms sulfur enhanced depolymerisability as predicted by DFT. Accordingly, our other CS2/OX OR polymers (Table , run #2 -#4) likewise undergo >99% depolymerisation under the above conditions into cyclic dithiocarbonates, while related polycarbonates show equilibrium limitations. Note that depolymerisation results in some reversion of the O/S exchange process and reshuffles the O and S centres from the OSO-alt-SSS links into cyclic dithiocarbonates containing one O and two S atoms. The CS2/OX copolymer likewise undergoes depolymerisation albeit necessitating higher dilution (0.023 M) for >99% depolymerisation. While depolymerisation of the nearly alternating copolymer ( Relative energies on the B3LYP/cc-pVDZ level of theory of cyclic versus polymer formation for the (a1) all-oxygen CO2/OX Me and (a2) the sulfurated CS2/OX Me cases as well as experimentally determined (de)polymerisation equilibria states under specified conditions; all-oxygen carbonate data displayed in reference to Endo and co-workers. 62 *note that P T as employed in the depolymerisation errors contains 8% OSO-alt-SSS errors; >99% depolymerisation products comprise of ca. 95% C T and 5% unidentified by-products. (b) ROCOP into depolymerisation into ROP sequence. ROCOP conditions as per Table run #1; depolymerisation conditions as per (a); ROP conditions 1 eq. 1,5,7-triazabicyclo[4.4.0]dec-5-en (TBD): 1 BnOH: 100 eq. C T , 4M in DCM, 20ºC, 16h, 45% conversion, obtained polymer P' T : Mn = 4.50 kg/mol, Đ = 1.22, Mn,theo = 7.29 kg/mol. (c) Overlaid 1 H NMR spectra (400 MHz, CDCl3, 25 ºC) of P T * produced by CS2/OX Me ROCOP, C T produced by depolymerisation and P' T produced by C T ROP. monomers during propagation. We probed this hypothesis by attempting to perform P T * depolymerisation in a 1:1 THF:CS2 mixture, in which metal-alkoxide chain-ends should insert CS2 forming less nucleophilic metaldithiocarbonate chain-ends and indeed did not find any depolymerisation to occur. In accordance with thermodynamically favoured depolymerisation, attempted ring-opening polymerisation of C T at 0.45M in THF does not occur, conditions under which C undergoes polymerisation. Nevertheless repolymerisation of C T can be achieved by solvent choice and concentration. Increasing the concentration to 4M in DCM with a 1,5,7-triazabicyclo[4.4.0]dec-5-en (TBD) and BnOH catalyst (1 TBD: 1BnOH: 100 C T , RT, 16 h) sufficiently shifts the (de)polymerisation equilibrium to achieve 45% ROP after 16 h (Mn = 4.50 kg/mol, Đ = 1.22, Mn,theo = 7.29 kg/mol) (Figure )). The ROP polymer P' T comprises OSO-alt-SSS (92%) and OSS (8%) links, which can be rationalized by chain-end alkoxide originated O/S exchange processes in reference to related reports by Buchard and co-workers. Similar to P T * (Tm = 107.2 ºC Tg = 5.5 ºC), P' T is semi-crystalline (Tm = 54.7 ºC Tg = -10.0 ºC) albeit with significantly lowered melting temperature by ca. 50ºC again highlighting how sequence selectivity achieved in the first place by LCrK enhances material properties. Subjecting P' T to the depolymerisation conditions outlined above likewise results in >99% depolymerisation under reversion of the O/S exchange process yielding C T highlighting the potential of our copolymers in the context of chemical recycling. Taken together our results indicate that CS2/OX ROCOP generates poly(dithiocarbonates) which are in a metastable or non-equilibrated state as a consequence of a sulfur induced ring-strain decrease. However, in ROCOP with LCrK metaldithiocarbonate formation at the propagating chain-end with CS2 limits the lifetime of metalalkoxide intermediates which are responsible for establishing (de)polymerisation equilibria into cyclic dithiocarbonate and for O/S scrambling. This does not (efficiently) occur in other ROCOPs and ROPs targeting related poly(thio)carbonates which gives reasons behind the selectivity benefits of LCrK over existing methodologies. As mentioned above, the high linkage selectivity achieved by LCrK can have a strong influence on the thermal properties of the obtained polymers. The CS2/OX copolymers with high OSS selectivity (i.e. Table ) crystallise from the reaction mixture at room temperature and hence exhibits semicrystallinity in the solid state as shown by DSC (Tm = 89.3 ºC, DHm = 36.01 J/g, Tc = 47.0 ºC for Table run #1 in the 2 nd DSC heating cycle, Figure ) and PXRD (primary reflections are observed at θ = 19.7º, 22.13º and 27.54º). Neither solution nor solid-crystallisation in DSC measurements is observed for the O/S-scrambled polymers (Table run #4 -#7) which are obtained as amorphous materials after removal of excess monomers and do not exhibit any semi-crystallinity by DSC (Tg = -29.1 ºC for Table 2 run #7). Owing to the low glass-transition temperature of these material, linkage selectivity is hence key to allow these materials to be hot pressed into free-standing and shape persistent films. Uniaxial tensile testing on films prepared from the polymer corresponding to Table run #9 shows a break at 3.6% elongation and a tensile strength of 20.6 MPa. Furthermore, dynamic mechanical analysis (DMA) shows a thermomechanical spectrum typical of a semi-crystalline material. A high maximum storage modulus of E' = 4.2 GPa is observed in the glassy state which decreases to E' ≈ 0.7 -0.3 GPa after an alpha glass transition at Ta = -14.7ºC (defined as the maximum of tan(d), d = E''/E', Figure ) which corresponds well to the Tg observed by DSC. A rubbery plateau is observed until the flow temperature at about 85ºC is reached for the semi-crystalline poly(trimethylenedithiocarbonate). Note that the all-oxygen analogue poly(trimethylenecarbonate) obtained from CO2/OX ROCOP has also been reported to be an amorphous material (Tg ~ -20 ºC). Our results hence indicate that the selective incorporation of sulfur centres leads to tighter packing of polymer chains than in the alloxygen case enabling semi-crystallinity and a regular polymer microstructure which is required to benefit from this effect. Although it has been previously reported that the formal substitution of sulfur for oxygen centres increases the crystallinity of polymers, the origins of this effect remain under debate. Shedding light on the origin of crystallinity, we computationally assessed the intermolecular association between two molecules for a series of mono-to tetrameric Me[(CH2)3-O-C(=E)-E-]nMe model dithiocarbonates (E = S) in comparison to the all-oxygen carbonate (E = O) counterparts (Figure , ESI Section S11). We chose linearly stretched conformations to maximize the interaction between the respective chains. In all cases, free energy optimisation results in face on association of the oligomers which maximizes the exposed surface area while minimizing the formation of hydrogen bonds or S•••S contacts which have previously been suggested to cause sulfur-induced crystallinity. AIM analysis reveals the absence of covalent interactions, indicating van-der-Waals forces to be the dominant form of attraction between chains. Attempted optimization of dimers without dispersion correction hence results in dissociation of the chains. Consequently, more polarisable sulfur centres should result in enhanced van-der-Waals interaction compared to the oxygen analogues. Accordingly, the association energy for dimerization decreases by ca. 25 kJ/mol on average per additional repeat unit n for E = O and by ca. 35 kJ/mol on average for E = S. Therefore, we suggest that increased interchain London dispersion contributes to sulfur induced semicrystallinity in our systems. In comparison the COS/OX copolymer shows a significantly higher Tm of 133ºC (vs. 89.3ºC for the CS2/OX copolymer) and enhanced hydrogen bonding interaction have been proposed to induce semi-crystallinity. Hence sulfur induced semi-crystallinity appears to arise through a combination of determinants exceeding the simple model outlined above.