COMPETITION BETWEEN CYCLOADDITION AND SPONTANEOUS COPOLYMERIZATION OF4-METHYL-1,3-PENTADIENE WITH ELECTROPHILIC OLEFINS

Competition between cycloadditions and spontaneous copolymerizations i n the reactions of 4-methyl-1,3-pentadiene (MPD; 1,1-dimethylbutadiene ) with seven electrophilic olefins was investigated at two temperature s (25 and 70-degrees-C) and in two solvents of different polarities (a cetonitrile and 1,2-dichloroethane). Tetracyanoethylene (TCNE), the mo st electrophilic olefin, reacted with MPD to produce a mixture of [2 2] and [4 + 2] cycloadducts, and the ratio of these isomers depended mainly on solvent polarity. No polymerization was observed in this sys tem. Both methyl beta,beta-dicyanoacrylate (MDA) and dimethyl cyanofum arate (DCF) reacted with MPD to produce mixtures of [4 + 2] and [2 + 2 ] cycloadducts and alternating copolymers. Reactions with fumaronitril e (FN), maleic anhydride (MAnh), and acrylonitrile (AN) with MPD produ ced only alternating copolymers and no cycloadducts. Trimethyl ethylen etricarboxylate (TrE), the least electrophilic investigated olefin, di d not react at all with MPD even at 70-degrees-C. All the obtained cop olymers are of high molecular weight (10(4)-10(5)). The suggested mech anism involves the formation of a 2-hexene 1,6-diradical formed by rea ction of the s-trans diene with the electrophilic olefin, which initia tes the diene-olefin alternating copolymerization. This polar diradica l is also the proposed intermediate in the [2 + 2] cycloaddition react ion. The diene in its s-cis conformation undergoes concerted Diels-Ald er cycloaddition with the electrophilic olefins.