Radical copolymerization behaviors of styrene and coumarin

Abstract

The radical copolymerizations of styrene (M1) with coumarin (M2) (and 7-acetoxycoumarin) have been first carried out in benzene (and in DMF) at 60° C using AIBN as initiator. The terminal model monomer reactivity ratios (MRR) were determined by Fineman-Ross method, Kelen-Tudos method and nonlinear method. The respective estimated values are r1 = 43.08, r2 = 0.63; r1 = 39.17, r2 = 0.43; and r1 = 49.94, r2 = 1.04 for styrene-coumarin (S-C) system. For styrene-7-acetoxycoumarin (S-AC) system, the values are r1 = 51.44, r2 = 1.24; r1 = 50.56, r2 = 1.20 and r1 = 56.23, r2 = 1.48, respectively. The penultimate model MRRs are determined by Fenn-Barson method and nonlinear method to be r1= 49.18, r1′ = 2.01, r2 = r2′ = 0.43 and r1 = 51.21, r1′ = 0.86, r2= r2′ =0, respectively, for S-C system; r1 = 64.76, r1′= 3.46, r2 = r2′= 1.20 and r1 = 59.90, r1 = 0.57, r2 = r2′ = 0. respectively, for S-AC system. It is found that coumarin is about 1.2 times more reactive toward styrene-terminated radical than 7-acetoxycoumarin for steric reasons. The penultimate model of Fenn-Barson is fairly adequate in describing the copolymerization mechanism of styrene-coumarin system, while the terminal model is more suitable for styrene-7-acetoxycoumarin system.