With the development of nanotechnology, the production and use of the nanocomposites has been increased. Polymer nanocomposites are among the most widely used nanocomposites. In this study, block copolymer and block copolymer-based polymer nanocomposites were synthesized and evaluated. For this purpose; firstly, poly(beta-butyrolactone)-b-poly(methyl methacrylate) [P(BL-b-MMA)] block copolymers were prepared simultaneously in one-pot by recycling additive/fragmentation chain transfer (RAFT) and ring-opening (ROP) polymerizations using a novel bifunctional RAFT-ROP agent which synthesized by chemical reaction with 3-bromo-1-propanol and potassium ethyl xanthate. Secondly, for the preparation of polymer nanocomposite, SiO2 nanoparticles were added to the prepared block copolymer with a rate of 3 wt% both during the polymerization stage and after the polymerization stage. The synthesized RAFT-ROP agent, block copolymer, and polymer nanocomposites were characterized using spectroscopic methods. The effect of copolymerization reaction conditions on molecular weight and molecular weight distribution (dispersity) was investigated. In one-pot copolymerization processes, relatively high weight copolymers were obtained by changing the copolymerization conditions due to the active centers in the copolymerization environment. The thermal characterization showed that the glass transition temperature of the block copolymer decreases with the addition of SiO2 during the polymerization stage and increases with the addition of SiO2 after the polymerization stage. SEM surface morphologies showed that block copolymer and polymer nanocomposites morphology is different from each other. The difference can be explained by the good dispersion of the block copolymer and SiO2 nanoparticles within each other.