Abstract: A polyester having dithiocarbamate group at its termini represented by the formula: ##STR1## wherein, in preferred embodiments, R.sup.1 and R.sup.2 are ethyl, R.sup.3 is ##STR2## R.sup.4 is --CH.sub.2 CH.sub.2 --, and R.sup.5 is ##STR3## The dithiocarbamate groups in the polymer can easily be dissociated upon irradiation with UV to produce polymeric free radicals, which can initiate an ethylenically unsaturated monomer to form a block copolymer of a molecular structure of ABA where B indicates a block corresponding to the polyester and A indicates a block of the monomer polymerized.