Well-defined high refractive index poly(monothiocarbonate) with tunable Abbe's numbers and glass-transition temperatures via terpolymerization

Abstract

The synthesis of thermoplastics with high refractive index (n) and high Abbe's number (V_d) is rarely reported. This work describes well-controlled synthesis of a soluble poly(monothiocarbonate) with high n and V_d values by using carbonyl sulfide (COS) as a source of sulfur. The alternating COS/cyclohexene oxide (CHO)/propylene oxide (PO) terpolymerization was performed by using a tetradentate Schiff base chromium chloride complex (SalenCrCl) and bis(triphenylphosphoranylidene) ammonium chloride (PPNCl) as a catalyst at 40 °C, yielding terpolymers with 100% poly(monothiocarbonate) selectivity based on the ¹H NMR spectra. The turnover frequency (TOF) of the SalenCrCl/PPNCl catalyst system was 323 h⁻¹ for COS/PO/CHO terpolymerization at 40 °C. The terpolymers possess number-average molecular weight (M_n) up to 22.3 kg mol⁻¹ with a narrow polydispersity index (PDI) of 1.16. These terpolymers exhibited high refractive indices (n) of 1.55–1.56. Of importance, by varying the feed ratio of PO and CHO, V_d of the resulting terpolymers was adjustable from 32.1 to 43.1, and the glass-transition temperature (T_g) varied from 43.7 to 93.4 °C. This poly(monothiocarbonate) might be used as optical plastics with tailored optical and thermal properties.