Method of preparing dimethylcetene and, subsequently, polydimethylcetene from isobutyric anhydride

A process for the preparation of dimethylketene (DMK) by pyrolysis of isobutyric anhydride (IBAN), in which:

• a) a mixture comprising 1 to 50% by volume of IBAN and 99 to 50% of inert gas is preheated at atmospheric pressure between 300 and 340° C.,
• b) this mixture is then brought to a temperature of between 400 and 550° C. for a contact time of between 0.05 and 10 s, in order to obtain a mixture of DMK, of inert gas, of isobutyric acid (IBA) and of unreacted IBAN,
• c) the mixture resulting from b) is cooled in a condensation stage, in order to separate the gas mixture comprising the DMK from the condensed IBA and/or condensed IBAN.