EFFECT OF ZNCL2 ON THE SPONTANEOUS COPOLYMERIZATION OF ACRYLONITRILE WITH SUBSTITUTED 1,3-DIENES

Acrylonitrile was allowed to react with three substituted hydrocarbon 1,3-dienes, namely, 2,3-dimethyl-1,3-butadiene (DMB), 4-methyl-1,3-pen tadiene (MPD), and Isoprene (IF) in 1,2-dichloroethane in the presence of various amounts of zinc chloride at different temperatures, Altern ating copolymers and [4 + 2] cycloadducts formed spontaneously. The st ructure of the diene and its electron-rich character control the produ ct distribution, In the reaction of DMB and AN, raising the temperatur e and increasing the ZnCl2 concentration enhance the cycloaddition pro cess, while the maximum yield of the copolymerization is at 45 degrees C; At higher temperatures, no copolymers formed. With MPD, only copol ymer is formed because the two terminal methyl groups preclude the con certed [4 + 2] cycloaddition. IF is less reactive than DMB, and. the o verall yields are lower. These results are in agreement with a postula ted mechanism involving competition between a pi-allyl 2-hexene-1,6-di radical and concerted cycloaddition. A II-transfer mechanism is sugges ted to explain the lack of copolymer for DMB/AN or IP/AN;at higher tem peratures and ZnCl2 concentrations.