DETECTION OF FERROELECTRIC TO PARAELECTRIC PHASE-TRANSITION IN COPOLYMERS OF VINYLIDENE FLUORIDE BY MAGNETIC-SUSCEPTIBILITY

The diamagnetic susceptibility of a series of random copolymers of vin ylidene fluoride (VF2) With trifluoroethylene containing 60 to 100 mol e-% VF2 has been investigated, both as a function of composition and o f temperature. Results show that at room temperature the molecular sus ceptibility of the series linearly decreases with VF2 content. Further more, the diamagnetic susceptibility for each composition rises gradua lly at the beginning of the Curie transition, reaching a plateau which characterizes the diamagnetism of the paraelectric phase. The percent increase in diamagnetism when passing from the ferroelectric to the p araelectric phase is primarily due to the changes occurring from the p lanar all-trans polar conformation into the disordered molecular confo rmation of the high temperature phase. The reduced final increase in d iamagnetism detected at the melting point suggests that conformational transformations occurring from the paraelectric phase into the molten state are small.