The development of thermally stable, highly transparent polymers with superior refractive indices and Abbe's numbers are important for the further development of next-generation technology such as miniaturized opto-integrated devices and advanced lenses. Highly transparent benzothiazole-based copolymers having either block or random sequences and high refractive indices were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The conventional free-radical and RAFT copolymerizations of 2-benzothiazolyl vinyl sulfide (BTVS) and 2-vinylnaphthalene (VNA) produced random copolymers with adjustable BTVS contents between 8 and 54%. Chain extending the macrochain transfer agent, which was prepared by the RAFT polymerization of BTVS, with VNA was well-controlled, enabling the synthesis of block copolymers with high BTVS contents (up to 70%) and reasonable polymer yields (up to 60%). The benzothiazole-based homopolymer, poly(BTVS), exhibited a high refractive index (1.7432) and a reasonable Abbe's number (17.0). Excellent transmittances (>93%) of 400 nm light were observed for both copolymers composed of BTVS and VNA, and high refractive indices of 1.7178-1.6672 were achieved. The resulting benzothiazole-based copolymers exhibited high refractive indices (>1.7), high transparencies, tunable low glass-transition temperatures (T-g = 75-150 degrees C), and high thermal stabilities (T-d5 > 240 degrees C) by adjusting the chemical structure, composition, and sequence of the comonomer. This report presents development of the first high-refractive-index polymers derived from S-vinyl sulfide derivatives with benzothiazole side chains, exhibiting the synergistic effects of combining aromatic naphthalene and heteroaromatic benzothiazole units.