Cold drawing of aliphatic ketone terpolymers with CH3 substituents is shown to promote production of the high density alpha crystal phase. The quantity of the minor alpha component decreases with increasing CH3 content and the solid-solid alpha --> beta phase transition temperature is shown to be lower compared with the unsubstituted polymer. Draw rate affects the amount of alpha phase produced: low draw rate favours alpha phase. This is explained in terms of strain-induced heating effects: high rates increase the temperature above the Talpha-->beta transition.