Combination of Photoinduced ATRP and Click Processes for the Synthesis of Triblock Copolymers

ABA type triblock copolymers possessing polystyrene as middle segment and poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) as side segments were synthesized by combining two photochemical strategies, namely photoinduced atom transfer radical polymerization (ATRP) and click processes. For this purpose, α,ω-diazido functional polystyrene (N3-PS-N3) was synthesized by photoinduced ATRP using a bifunctional initiator, followed by a simple substitution of the chain end halides. Parallel to this, alkyne-PCL was synthesized by ring opening polymerization of ε-caprolactone, employing propargyl alcohol as initiator. For the synthesis of alkyne-PEG, industrially available PEG was functionalized by a simple esterification reaction using 5-pentynoic acid. After the syntheses of these alkyne functional polymers as clickable counterparts, they were reacted with N3-PS-N3 by photoinduced click reactions to prepare the desired triblock copolymers. All polymers were characterized by NMR, IR and GPC analyses.