AbstractThe homopolymerisation of 2‐furaldehyde, 5‐methyl‐2‐furaldehyde and 2‐furyl methyl ketone and their cationic copolymerisation (BF3. Et2) with olefins were investigated. All attempts to obtain homopolymers failed because of thermodynamic restrictions. 2‐Furaldehyde and α‐methylstyrene gave an alternating copolymer of low degree of polymerisation, 2‐methyl‐2‐furaldehyde and α‐methylstyrene gave copolymers rich in 5‐methyl‐2‐furaldehyde, indicating a penultimate effect in the growth mechanism. The use of less basic comonomers (cyclopentadiene, styrene, isoprene, etc.) resulted in inhibition or strong retardation of the polymerisation. The use of more basic comonomers (acenaphthy‐lene,N‐vinylcarbazole) resulted in their homopolymerisation. Furyl methyl ketone inhibited the polymerisation of all comonomers tried. A complex between BF3. Et2O and 2‐furaldehyde was isolated and characterised. A general mechanism is offered to exp