End-functional polystyrenes with an N,N-diethyldithiocarbamyl group were prepared by the photopolymerization of styrene with novel diethyldithiocarbamate derivatives as photoiniferters. Under ultraviolet light, the end-functional polymers could initiate a second monomer to polymerize and form block copolymers, such as polystyrene-b-poly(methyl methacrylate), polystyrene-b-poly(vinyl acetate), and polystyrene-b-poly(n-butyl acrylate). According to end group analysis and electron spin resonance (ESR) spectroscopy, AB-type block copolymers were produced. The glass transition temperature and thermal stability of the block copolymers were investigated by means of thermal analysis.