Kinetics and mechanism of the isomerization polymerization of 2‐methyl‐2‐oxazoline by benzyl chloride and bromide initiators. Effect of halogen counteranions

Kinetic studies of the isomerization polymerization of 2‐methyl‐2‐oxazoline ( 2 ) initiated with benzyl chloride ( 1a ) or bromide ( 1b ) were carried out by NMR spectroscopy. The polymerization initiated with 1a proceeded exclusively via a covalently bonded alkyl chloride species 5 , whereas the polymerization of the system initiated with 1b proceeded via a oxazolinium bromide 10 as the propagating end. The propagation rate constant k p with 1a was about 1/40 of that found with 1b at 40°C in CD 3 CN. The mechanistic difference is explained by the different nucleophilicities of the counteranions, Cl — and Br — . A model compound for the propagation with 1b as initiator was also examined changing the temperature and the solvent.