Block copolymers of poly(N-decylacrylamide-b-N,N-diethylacrylamide) (PDcA-b-PDEA), With different PDEA block lengths and a constant PDcA block labeled with a phenanthrene fluorescent dye at the PDcA alpha-chain-end were prepared by RAFT polymerization. These copolymers form star-like micelles in water, (critical micelle concentration below 0.1 g/L, determined using coumarine 153) witha PDcA insoluble Core Surrounded by a PDEA corona showing thermoresponsive properties. The kinetics of Forster resonance energy transfer (FRET) between the chain-end phenanthrene groups and anthracene loaded into the hydrophobic core of (lie micelles in water, was analyzed using it new model for energy transfer ill spherical nanodomains. This model takes into account the Poisson distribution of the acceptors in the micelle population and the existence of two phenanthrene states with different fluorescence lifetimes. The analysis yields the radius of the micelle core. R-c = 2.7 +/- 0.1 nm, with no need for deuteration of the core block. The analysis is compared with the Value obtained by extrapolation of the light scattering data using the star micelle model, R-c(DLS) = 3.0 nm. The model for star-like micelles also yields it solvent-corona interaction parameter (hill changes with temperature due to the thermoresponsive nature of PDEA.