NICKEL(0)-CATALYZED 1-1 CYCLOADDITION COPOLYMERIZATION OF 1,3-AND 1,4-DI(2-HEXYNYL)BENZENES WITH CARBON-DIOXIDE TO POLY(2-PYRONE)S

A nickel(0) catalyst generated from Ni(COD)2 and triethyl- or tri-n-octylphosphine effected efficient 1:1 cycloaddition copolymerization of 1,3- and 1,4-di(2-hexynyl)benzenes (1 and 2) with CO2 to poly(2-pyrone)s 3 and 4, respectively. Copolymerization of 1 with CO2 at 80-degrees-C in THF/MeCN for 20 h under a CO2 pressure of 10-50 kg/cm2 afforded 3 with molecular weights of 6000-7000 in ca. 50% yield, and copolymerization of 2 with CO2 at 70-degrees-C in THF/MeCN for 20 h under a CO2 pressure of 20-50 kg/cm2 afforded 4 with molecular weights of 9000-12 000 in ca. 60% yield. Formation of the poly(2-pyrone) was demonstrated by IR, H-1 NMR, and C-13 NMR spectroscopies and by measuring the content of the 2-pyrone ring in the copolymer by IR spectroscopy using a cooligomer as an IR standard.