CHAIN-LENGTH EFFECTS ON CRYSTAL-FORMATION IN VINYLIDENE FLUORIDE OLIGOMERS

Crystal modifications in vinylidene fluoride (VDF) oligomers, such as alpha, beta, and gamma forms, were studied as a function of the molecu lar chain length. VDF oligomers were prepared by a telomerization meth od and the oligomers were fractionated by vacuum vapor deposition. The fractionated oligomers were crystallized from the melt. The crystal f orms in VDF oligomers were characterized by IR, X-ray, and DSC methods . The beta form was found in the degree of polymerization (N) less tha n 10, the alpha form consisted of N ranging from 10 to 16 and the gamm a form was observed in N above 16. The effect of molecular chain lengt h on the crystal forms in VDF oligomers could be associated with chang e in the conformational energy accompanying the steric hindrance along the molecular chain for the beta form and differences in the crystall ization behavior from the melt for the alpha and gamma forms.