In an initial attempt to achieve S8/CS2/PO ringopening terpolymerisation (ROTERP) at room temperature, we tested the polymerisation with 1 eq. lithium benzyl oxide (LiOBn, generated from Li[N(SiMe3)2] and BnOH, see ESI Section S2), 250 eq. PO, 500 eq. CS2 and 125 eq. S (i.e. 1/8 S8) ( ); these resonances can be tentatively assigned in reference to the copolymers produced by ROCOP of CS2/PO and S8/PS. In addition to formation of 84% polymer (i.e., polymer selectivity is 84%), we also obtained approximately 16% cyclic fivemembered propylene dithiocarbonate (dt-c5c) byproduct; this can be easily removed from the crude reaction mixture by precipitation from DCM/MeOH. 2D NMR spectroscopy of the isolated polymer showed tertiary carbons ((C t ) = 78 ppm) bound to OSO ((C q ) = 193 ppm) links and secondary carbons ((C s ) = 43 ppm) adjacent to Sx links. Hence the copolymer exhibits a poly(OSO-alt-Sx) microstructure in head-to-head-alt-tail-to-tail regioselectivity, which is reminiscent of the poly(OSO-alt-SSS) structure described by Komber and Werner et al. with Sx in place of trithiocarbonate links. The selectivity of OSO and Sx versus other links (e.g. dithio-OSS and trithiocarbonate SSS) is 98%. No (thio)ether links could be observed. GPC analysis reveals an apparent weight-average molar mass of the copolymer of Mw = 20 kDa (Đ = 1.7). Note that during this process H2S evolution did not occur, which otherwise is a common problem in other S8 copolymerisations. e Determined by GPC (gel permeation chromatography) measurements conducted in THF with polystyrene calibration. f 1 eq. Ph3NPh3Cl:400 eq.PS: 400 eq. S with 50vol% toluene in Reference to Ref. g Na was used as catalyst instead of Li. h K was used as catalyst instead of Li.