Photopolymerization of Liquid Carbon Disulfide Produces Nanoscale Polythiene Films

• Published in: Journal of the American Chemical Society 2001-02, Vol.123 (6), p.1199-1207
• Main Authors: Zmolek, Peter B, Sohn, Honglae, Gantzel, Peter K, Trogler, William C
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja003200j

Broad band solar or 300−400 nm irradiation (Hg−Xe arc source) of liquid-phase carbon disulfide produces a new carbon−sulfur polymer with the approximate (n = 1.04−1.05) stoichiometry (CS n ) x . The polymer, from here on called (CS) x , forms as a ∼200 nm thick transparent golden membrane as measured by SEM and AFM techniques. IR spectra for this polymer show some similarities with those obtained for the gas-phase photopolymerized (CS2) x and the high-pressure-phase polymer of CS2, called Bridgman's Black. The observed FT-IR absorptions of (CS) x include prominent features at 1431 (s, br), 1298 (m), 1250 (ms), and 1070 cm-1 (m). In contrast to previous proposals for (CS2) x , 13C labeling and model compound studies of α-(C3S5)R2 and β-(C3S5)R2 (R = methyl or benzoyl) suggest that the absorption at 1431 cm-1 and those at 1298 and 1250 cm-1 are indicative of carbon−carbon double bonds and carbon−carbon single bonds, respectively. The molecular structure of α-(C3S5)(C(O)C6H5)2, determined at −84 °C, belongs to space group P1̄, with a = 7.486(5) Å, b = 13.335(11) Å, c = 17.830(13) Å, α = 105.60(6)°, β = 95.32(6)°, γ = 90.46(6)°, Z = 4, V = 1706(2) Å3, R = 0.0785, and R w = 0.2323. With use of electron and chemical ionization mass spectrometry, C4S6 and C6S7 were identified as the dominant soluble molecular side-products derived from a putative ethylenedithione (SCCS) precursor. Atomic force microscopy (AFM) provided surface topology information for the thin film (CS) x and revealed features that suggested the bulk material is formed from small polymer spheres 20−50 nm in size. Both (CS2) x and (CS) x are extensively cross-linked through disulfide linkages and both materials show strong EPR resonances (g > 2.006) indicative of sulfur-centered radicals from incomplete cross-linking. A polymerization mechanism based on the intermediacy of S2CCS2 is proposed.