Controlled carbocationic polymerizations of bicyclo2.2.1hepta-2,5-diene with AlCl3 in the presence of electron pair donor components

摘要

The cationic isomerization polymerization of bicyclo2.2.1hepta-2,5-diene (norbornadiene) was investigated. The synthesis of gel-free poly(3,5-tricyclo2.2.1.0(2,6)heptylene) was achieved at a reaction temperature of 0 degrees C. These polymerizations were initiated by AlCl3 in the presence of the weakly donating additives nitrobenzene or nitromethane. NMR spectra show that the polymer contains a small fraction (between 2 and 4 mol-) of branched structures in addition to a small amount of 5,7-linked bicyclic olefin units (approximately 2). A reaction mechanism involving non-classical carbocation intermediates is proposed in order to account for the 5,7-enchainment of the bicycloheptenylene units, which contrasts with earlier studies on cationic norbornadiene polymerizations. Further, pentamethylbenzene was utilized as a chain transfer reagent in order to adjust the number average molecular weight (M) over bar(n) to values below 2500. References: 56