The invention relates to a method for producing non-alternating formaldehyde/CO2 copolymers, said method comprising the step of reacting formaldehyde or a compound that releases formaldehyde with carbon dioxide in the presence of a catalyst system. Said method is characterized in that the catalyst system comprises a Lewis acid component and a basic component, the Lewis acid component being at least temporarily coordinatively unsaturated under reaction conditions and the basic component having a pKb value of >=0.