Kinetic and ESR studies on the radical polymerization. radical‐initiated copolymerization of the diethyl itaconate‐SnCl₄ complex and styrene

The copolymerization of diethyl itaconate (1) (M 1 ) and styrene (2) (M 2 ) with dimethyl 2,2′‐azoisobutyrate ( 3 ) was performed in benzene at 50°C, and the following copolymerization parameters were obtained: r 1 = 0,34, r 2 = 0,35, Q 1 = 0,93 and e l = +0,66. The copolymerization system was found to involve ESR 1 Electron spin resonance. ‐observed propagating polymer radicals at low monomer feed composition ( f 2 ) of 2 . The apparent rate constant of termination increased rapidly with f 2 . The ESR‐determined values of the apparent propagation rate constant of the copolymerization were lower than those calculated on the basis of the Mayo‐Lewis model, suggesting a significant penultimate effect in the copolymerization. On the other hand, the copolymerization of the 1 ‐SnCl 4 complex (M 1 ) and 2 (M 2 ) at 50°C yielded a nearly alternating copolymer independently of the monomer feed composition. The propagating polymer radicals were ESR‐observable even up to f 2 = 0,8. The ESR‐determined apparent rate constant ( k p ) of propagation showed a maximum near f 2 = 0,5. From the relationship between k p and f 2 , the rate constants of cross‐propagations of the present alternating copolymerization were evaluated as k 12 = 483 and k 21 = 510 L. mol −1 · s −1 . Comparison of the k 21 value and the reported propagation rate constant (209 L · mol −1 · s −1 ) of homopolymerization of 2 leads to the conclusion that the alternating copolymerization via free‐monomer propagation mechanism originates from a pronounced penultimate effect suppressing homopropagation of 2 , but not from enhanced cross‐propagation.