Synthesis of Sulfur-Rich Polymers: Copolymerization of Cyclohexene Sulfide and Carbon Disulfide Using Chromium Complexes

The copolymerization of cyclohexene sulfide (CHS) and carbon disulphide (CS2) to afford poly(cyclohexene) tritiocarbonates catalysed by a chromium complex with salen-type ligand 1 (R,R)-N,N?-bis(3,5-di-tertbutylsalicylidene)-1,2-diaminobenzene has been studied in the presence of [PPN]N3 (bis(triphenylphosphine) iminium azide) as cocatalyst at different temperatures and comonomer loading (Figure 1). A kinetic study was carried out in order to identify the optimal conversion and selectivity. The reaction proceeds with higher selectivity values at 25 °C, with 2:1 CS2 to CHS loading ratio and the polytritiocarbonate copolymer is the dominant product. Moreover, the 1 H and 13C NMR spectra shown only 3% of signals related to the thioether moiety. Therefore, it can be assumed that the samples are mainly alternating copolymers. The polytritiocarbonate copolymer synthetized with salen-type ligand 1 shows higher molecular weight than copolymers from literature prepared with chromium complex with salen-type ligand 2 (N,N'-bis(3,5-di-tertbutylsalicylidene)-1,2-ethylenediamino) where the copolymerization yields only 15 % of copolymer with a molecular weight (Mw) of about 5000 g/mol. The thermal behaviour of the copolymers was studied by TGA and DSC. The sulphur-rich polythiocarbonates decompose with a midpoint temperature of about 250 °C. A crystallization temperature, not observed in polycarbonates, is detected at 113 °C and additionally the sulphur-rich samples exhibit a melting temperature around 147°C.