Growth kinetics of CdSe nanocrystals generated inside three selected polymers (polyvinylpyrrolidone--PVP, polyethyleneglycol--PEG and polyvinylalcohol--PVA) are demonstrated to follow a self-catalytic path, with growth rates depending on the nature of the polymer, i.e. on the capability to activate the cadmium species present in the solution of a metal precursor. A two-step process drives the size evolution of nanocrystals and a critical diameter value can be identified at which the growth regime changes. The medium-term stability evaluation of nanocomposites indicates that, after an initial rearrangement, polymers keep stable the embedded CdSe nanocrystals.