Well-defined high refractive index poly(monothiocarbonate) with tunable Abbe's numbers and glass-transition temperatures via terpolymerization
The synthesis of thermoplastics with high refractive index (n) and high Abbe's number (Vd) is rarely reported. This work describes well-controlled synthesis of a soluble poly(monothiocarbonate) with high n and Vd 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 (Mn) 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, Vd of the resulting terpolymers was adjustable from 32.1 to 43.1, and the glass-transition temperature (Tg) varied from 43.7 to 93.4 °C. This poly(monothiocarbonate) might be used as optical plastics with tailored optical and thermal properties.