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-tert-butylsalicylidene)-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). Figure 1. Copolymerization of cyclohexene sulphide (CHS) and CS2. 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 1H 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 shown higher molecular weight than copolymers from literature and prepared with chromium complex with salen-type ligand 2 (N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediamino) where the copolymerization yields only 15 % of copolymer with a molecular weight (Mw) of about 5000 g/mol1. 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. References: [1] D.J. Darensbourg, J. R. Andreatta, M. J. Jungman, J. H. Reibenspies, Dalton Trans. 2009, 8891-8899.