Telechelic thermo- and light-responsive polymers based oil poly(oligo(ethylene glycol) methyl ether methacrylate) P(OEGMA) with azobenzene functionalities at the end groups were synthesized. In a reversible addition-fragmentation chain transfer (RAFT) polymerization using a functionalized chain transfer agent (CTA) containing a pentafluorophenyl (PFP) activated ester, oligo(ethylene glycol) methyl ether methacrylate (OEGMA, M-n similar to 300 g mol(-1)) could successfully be polymerized with good control over molecular weight, very high conversions, and narrow molecular weight distributions. Polymers derived from this CTA possessed an activated ester at the alpha-end of the polymer chain as well as a dithioester omega-terminus. The omega-dithioester group of each polymer chain could quantitatively be either retrieved with AIBN treatment or Substituted with a PFP ester by using a modified diazo compound. As a consequence, a postmodifiaction of the telechelic reactive end groups was possible through it polymer analogous reaction with amino-functionalized azobenzene. P(OEGMA) polymers containing azobenzene end groups showed a reversible light- and temperature-controlled phase transition in water. Higher values for the lower critical solution temperature (LCST) were measured after irradiation of the aqueous polymer solutions due to the higher polarity of cis-azobenzene. The LCST differences between irradiated and nonirradiated solutions increased linearly upon the ratio of azobenzene units up to 4.3 degrees C.