Simulations by dissipative particle dynamics revealed a possibility to produce micelles of diverse morphologies via irreversible end-coupling reaction in polymer melts containing a particulate phase. It is demonstrated that the reaction at the surface of a polymer A droplet immersed in a melt of polymer B leads to the droplet instability and subsequent micelle formation. Depending on the length ratio of reacting chains and its own size, the droplet is either emulsified into a set of small micelles or converted into a single micelle, which can have rather complex internal structure. A morphology diagram containing structures that are typical for polymer solutions, in particular vesicles, bowls, worms, star-like and crew-cut micelles with multiple internal domains, is first presented for polymer melts. Investigation of the reaction kinetics reveals subsequent linear, saturation, and exponential autoacceleration regimes. By simulations and using simple scaling arguments, it is explained how the barrier properties of a diblock copolymer layer formed at the A/B interface depend on the copolymer composition and droplet curvature. It is found that the scenario of the instability development is much different for flat and spherical A/B interfaces.