Synthesis of poly(ethylene adipate) with a stable nitroxyl radical at both chain ends, and applications to a counter radical for living radical polymerization

Synthesis of poly(ethylene adipate) (PEA) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) at both chain ends was attained by reaction of 4-hydroxy-TEMPO and PEA with isocyanate groups at the terminals. PEA obtained was found to have the living nitroxyl radical, because the electron spin resonance (ESR) spectrum of the polymer manifested a typical three sharp signals based on TEMPO. TEMPO-supported PEA served as a polymeric counter radical for the radical polymerization of styrene, to quantitatively give the block copolymer of ethylene adipate and styrene. Polymerization proceeded in accordance with a living mechanism, because the molecular weight of the copolymer was proportional to conversion of styrene and reciprocal of initial concentration of TEMPO attached to PEA. Analysis of the copolymer using a thin layer chromatography/flame ionization detection (TLC/FID) clarified that the copolymer contained no homopolystyrene. This absence of homopolystyrene implies that no diblock copolymer is formed during polymerization. H-1 NMR analysis demonstrated the structure of copolymer obtained to be A-B-A triblock.