The microphase-separated bulk structure was further revealed by atomic force miscroscope images of the spin-coated thin film (Fig. ). Moreover, such block copolymers demonstrate high thermal stability with Td,5% (decomposition temperature of 5% in mass fraction) of 233 to Optical properties of block copolymers. Our method is also a convenient way to synthesize sulfur-containing block copolymers. Sulfur atoms endow block copolymers with desirable optical properties. As the polythiocarbonate content increases from 33 to 91 mol%, the refractive index (nd) of the diblock increases from 1.47 to 1.58 (at wavelength of 587.6 nm), as determined by spectroscopic ellipsometer (Fig. ). By contrast, the PLA homopolymer has a lower nd of 1.47. The outstanding optical and mechanical properties demonstrate broad application prospects of these materials in the field of optoelectronics.