Block and star block copolymers by mechanism transformation. I. Synthesis of PTHF‐PSt‐PTHF by the transformation of ATRP into CROP

Polystyrene (PSt) with end‐terminal bromine (Br‐PSt‐Br) was synthesized by the atom transfer radical polymerization of styrene with the difunctional initiator 1,2‐bis(2′‐bromobutyryloxy)ethane in combination with CuBr and bipyridine. The Br‐PSt‐Br reacted with silver perchlorate at −78 °C, and the resulting macromolecular initiator was used to initiate the polymerization of tetrahydrofuran. Triblock poly(tetrahydrofuran)‐polystyrene‐poly(tetrahydrofuran) (PTHF‐PSt‐PTHF) diol was obtained after propagation at −15 °C. The conversion of the polymerization was measured by gas chromatography. The structures of the triblock copolymer PTHF‐PSt‐PTHF diol were characterized by ¹H NMR and gel permeation chromatography. The mechanism of cationic ring‐opening polymerization is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 337–344, 2000