Influence of Polymer End Groups on Crystallization and Morphology of Poly(vinylidene fluoride) Synthesized in Homogeneous Phase with Supercritical Carbon Dioxide

Abstract

Poly(vinylidene fluoride) (PVDF) samples from homogeneous phase polymerizations in supercritical CO2 and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs, and morphology. Upon expansion the polymer was obtained as white particles. Scanning electron microscopy showed that DTBP (di-tert-butyl peroxide) derived polymer end groups lead to stack-type particles whereas sponge- or rose-type particles were obtained in case of chain transfer agent fragments as end groups. FTIR (Fourier-transform infrared spectroscopy) and WAXD (wide-angle X-ray diffraction) indicated that the type of polymorph, α or β crystal phase, is significantly affected by the type of end group. In addition, the crystallinity of the material, as determined via differential scanning calorimetry, is affected by the end groups and polymer molecular weights. For example, with M n around 6700 g·mol−1 crystallinity ranges from 29% for DTBP-derived endgroups to a maximum of 64% for end groups originating from perfluorinated hexyl iodide used as chain transfer agent during polymerization.

Effect of Chain Transfer Agents on Kinetics and Morphology of Poly(vinylidene fluoride) Synthesized in Supercritical Carbon Dioxide

“…For PVDF with C 6 F 13 Br-derived (PFHB) or DTBP-derived end groups (DTBP) the weight loss at 300 8C amounts to 6 and 9%, respectively. These results are also in line with crystallinity data, since for DTBPderived end groups the crystallinity is below 30%, [26] whereas bromine containing CTA results in polymer with 52% of crystallinity. In view of the large variations in crystallinity the differences in TGA curves seem rather small.…”

“…H-NMR spectrum in Figure 2 refers to PVDF from a reaction with C 6 F 13 Br. The following peaks may be assigned to the major structural units: [26] -CF 2 -CH 2 -CH 2 -CF 2 -multiplet; 2:35 ppm ÀCH 2 -CF 2 À multiplet; 2:94 ppm C 6 F 13 À CH 2 À triplet; 3:24 ppm -CH 2 -CF 2 -Br quintet; 3:56 ppm H-CF 2 -CH 2 -triplet of triplet;6:3 ppm…”

“…From Figure 2 and 3 the fraction of defect structures is calculated to be 8%, which is close to the value of 7% derived for PVDF with C 6 F 13 I-derived end groups. [26] Thus, the fraction of defect structures is independent of how molecular weights are controlled. As indicated by the low intensities of the 1 H-NMR peaks at 6.3 in Figure 2 and 3 the contributions from chain transfer of H, e.g., via transfer to polymer, are minor.…”

“…Previously, the latter assignment was confirmed by wide angle X-ray scattering and it was shown that PVDF with C 6 F 13 I-derived end groups shows the lowest content of b phase material compared to PVDF with methyl or BrCCl 3 -derived end groups. [26] The overall degree of crystallinity determined via differential scanning calorimetry (DSC) was highest for PVDF with C 6 F 13 Iand lowest for DTBP-derived end groups. Comparison of IR spectra for PVDF with C 6 F 13 I and C 6 F 13 Br-derived end groups indicates that the fraction of b phase material is higher for the bromine end group.…”

Effect of multiwalled carbon nanotubes on crystallization behavior of poly(vinylidene fluoride) in different solvents

“…8,9 Other methods for obtaining b-phase have also been proposed. [10][11][12] Typically, supercritical carbon dioxide (SC CO2) method, 13 electrospinning technique, 14,15 and strong electric field 16 have also been explored. In addition, the incorporation of nanoparticles into PVDF could also influence the crystallization of PVDF in that PVDF chains are confined by the dispersed nanoparticles, then resulting in different crystallization behaviors and structures.…”