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 Encyclopedia of Physical Science and Technology  en012f-594  July 26, 2001  11:9







              Polymers, Ferroelectric                                                                     667

              TABLE II A Summary of VDF/TrFE/CTFE Terpolymers Prepared by Borane/Oxygen Initiator a
                      Terpolymer           Melting     Phase transition
                       mole ratio         temperature   temperature
                                                                       [η]
              Sample                     T m   ∆H m    T C    ∆H C    (MEK) b  P max    E c   Dielectric  Dielectric
                                                                                  2
               no.   VDF   TrFE   CTFE   ( C)  (J/g)  ( C)    (J/g)   (35 C)  (mC/m )  (MV/m)  constant c  loss
                                                                        ◦
                                                       ◦
                                         ◦
                1    72.2   17.8   10.0  107.8  17.8  25.0     0.4     0.38     82     19.6     27.0     0.04
                2    66.0   22.5   11.5  117.2  21.6  25.2     2.5     0.42     78     24.1     22.4     0.03
                3    66.1   21.4   12.5  115.6  20.5  25.8     1.8     0.42     —       —       40.9     0.04
                4    63.1   25.4   11.5  113.7  18.5  None d  None     0.49     76     19.8     53.5     0.06
                5    61.4   25.3   13.3  111.3  17.8  15.6     1.5     0.69     75     33.7     53.1     0.06
                6    58.0   33.1   8.9  130.0   21.3  31.6     2.5     0.63     63     16.4     33.0     0.05
                7    60.0   36.0   4.0  140.9   25.7  43.8     6.5     0.58     87     21.8     26.4     0.04
                8    55.6   36.1   8.3  124.6   21.2  None    None     0.54     36      7.6     42.4     0.07
               9 e   60.0   35.1   6.9  126.6   20.9  33.5     1.6     0.78    110     55.9     52.7     0.07
               10 e  59.3   32.9   7.8  125.1   20.3  24.8     1.4     0.80     70     11.5     51.0     0.07
               11 e  57.3   31.2   11.5  111.1  14.8  None    None     0.75     45     39.4     50.5     0.06
                a                        ◦                                  ◦
                 P max and E c at 100 MV/m, 10 Hz, 22 C. Dielectric constant and dielectric loss at 1 KHz, 22 C.
                b
                 MEK, methylethylketone.
                c
                 Value measured in the heating cycle.
                d
                 None: no observable.
                e
                 Sample prepared by constant monomer feed ratio during the polymerization.
              the insertion of monomers in a preferred head-to-tail se-  removed  by  methanol.  Table  II  summarizes  several
              quence. No chain transfer and termination reactions are  VDF/TrFE/CTFE terpolymers prepared by the same
              expected during the propagating process, which will lead  method. All terpolymers are high-molecular-weight
              to a linear polymer structure with relatively narrow molec-  (>20,000 g/mole) polymers with good solubility in com-
              ular weight and composition distributions. Figure 5 shows  mon organic solvents and are melt processable at >150 C.
                                                                                                           ◦
              that the VDF/TrFE/CTFE terpolymer increases in molec-
              ular weight with the conversion of monomers.
                                                                B. Thermal Properties
                In addition, this chemistry produces terpolymers that
              have relatively uniform molecular structure and few  Despite having relatively high concentrations of CTFE
              impurities (boric acid and butanol), which can be easily  units, all the terpolymers are still semicrystalline thermo-
                                                                plastics with melting temperatures >100 C and a crys-
                                                                                                 ◦
                                                                tallinity  of   H > 17  J/g.  Figure  6  compares  the  DSC
                                                                curves of three VDF/TrFE/CTFE terpolymers (samples
                                                                9, 10, and 11). The relatively well-defined melting and
                                                                crystalline phase transition temperatures imply arelatively
                                                                uniform molecular structure and polymer morphology.
                                                                In addition to the reduction of melting temperature, the
                                                                incorporated CTFE units also significantly reduced the
                                                                F–P phase transition temperature. It is interesting to note
                                                                that the effect of incorporated CTFE units resembles that
                                                                seen from crosslinking in irradiated VDF/TrFE samples.
                                                                The CTFE units may not affect the crystal unit cell of
                                                                VDF/TrFE segments, and instead serve as a defect (by in-
                                                                troducing a gauche bond) to prevent the extension of crys-
                                                                tallization, which results in the reduction of the lamella
                                                                thickness of the crystal. Detailed studies of the molecular
                                                                structure and the crystal polar domain size are underway.
                                                                  In general, the third CTFE monomer units in VDF/
              FIGURE 5 Intrinsic viscosity of VDF/TrFE/CTFE terpolymer ver-  TrFE/CTFE terpolymers shift (and broaden) the phase
              sus monomer conversion.                           transition to lower temperatures, to near ambient
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