Effect of tetra‐n‐butylammonium bromide salt on the cationic polymerization of dimethylketene and on the thermal properties of the obtained polyketones

The cationic polymerization of dimethylketene is achieved in dichloromethane at −30 °C, using a stoichiometric mixture of aluminum bromide (AlBr3) and tetra-n-butylammonium bromide (n-Bu4N+Br−) as initiator. Characterizations by 1H and 13C NMR show that the resulting polymers have a perfect polyketonic microstructure. Capillary viscosity, DSC, and SEC analysis show that for a constant monomer/initiator ratio, polymers synthesized in the presence of tetra-n-butylammonium bromide are more crystalline and have better properties than those produced only with AlBr3. Melting temperatures, inherent viscosities and average molecular weights are systematically higher. A good linearity is observed between ln (inherent viscosity) versus ln Mn ¯theory  for the system with n-Bu4N+Br−, showing a good control of the molecular weight by the initial feed ratio. The effect of this compound suggests a reversible equilibrium between active and dormant species, which limits the transfer and/or termination reactions, and enables a better control of the cationic polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1493–1499