Cationic polymerization of dimethyl ketene

By ionic polymerization, dimethyl ketene can lead to polyketone, polyester or polyacetal. In the presence of AlBr₃ as Lewis acid initiator, pure polyketone can be obtained in nitrobenzene/carbon tetrachloride (50/50, v/v). With other cationic initiators or solvents, a mixture of polyketone and polyester was characterized. According to experimental conditions, a cyclic trimer was also observed by backbiting reaction, a cyclic dimer by heating to room temperature and a cyclic lactone when acetone was used as solvent. ¹³C n.m.r. is the most effective technique to determine polyketone purity. For example, an important modification of f.t.i.r. spectrum was noticed after melting and crystallization of the polymer with appearance of new bands which could correspond to polyester or polyacetal bands regarding to literature data. In fact, these bands correspond to change in morphology and ¹³C n.m.r. spectrum shows no structure modification. Polyketone degradation occurs at about 340 °C and the polymer is stable for several hours at 205 °C.