The micro-structure of poly(vinylidene fluoride) oligomers was characterized by 19F and 13C n.m.r. and the effects of molecular weight and the chain end groups on the crystal forms were studied by i.r. and X-ray methods. One of the oligomers terminated with -CH3 and the fragment of an initiator at the chain ends. The other oligomers were terminated with -Cl and CCl3- at their chain ends. The larger chain end groups tended to produce the conformational disorder in the molecules yielding the γ form. The smaller molecular weight of the oligomer gave rise to the β form. © 1997 Elsevier Science Ltd. All rights reserved.