Study Of High/Medium Temperature Dispersion Polymerization And Low Temperature Solution Polymerization Of Vinylidene Fluoride Initiated By Organic Peroxide

The nucleation mechanism and particle growth of VDF dispersion polymerization were studied systematically in this thesis. Based on the nucleation theory of dispersion polymerization and19F-NMR and FT-IR analysis, oligomer nucleation was identified as the main mechanism in the dispersion polymerization of vinylidene (VDF). The relationship between the reaction pressure (P), initial initiator concentration (p1.0), surfactant concentration (ps) and PVDF latex particle size (d) was determined as d～P120ΡI,0-0.76ΡS-0.33and the relationship between conversion (X) and d was d～X0.36, among which the reaction pressure (or monomer mass concentration) was found to be the most effective factor. Some properties (melting point, molecular weight, chain configuration, crystal form etc) were analyzed during the period of particle growth.Based on the oligomer mechanism of dispersion polymerization and the free radical polymerization theory, a polymerization kinetic model of vinylidene difluoride monomer was established in this thesis. Then high-temperature polymerization and medium-temperature polymerization experiments were conducted in a horizontal reactor. The high-temperature polymerization was initiated by di-tert butyl peroxide (DTBP) and the medium-temperature polymerization initiated by di-isopropyl peroxydicarbonate (IPP). The effect of p1, Pm and ps on the reaction rate (Rp) and particle number per unit volume (Np) were studied. In120℃high-temperature polymerization,Np=4.72×1017ΡS0.99ΡI,02.31ΡM-3.58and Rp=2.50×10-6φ1/3ΡS0.16Ρ10.43ΡM1.85. In50℃medium-temperature polymerization, Np=1.01×1019ΡS1.92ΡI,0ΡM-3.11and Rp=1.76×10-8φ1/3ΡS0.36ΡI0.60ΡM3.83.Rp can be further related to the power of Np, and the index was0.16and0.19for medium and high-temperature polymerization, respectively, very close to the theoretical value of1/6in the kinetic model for VDF dispersion polymerization.Low-temperature radical solution homopolymerisation of vinylidene fluoride (VDF) and copolymerisation of VDF with perfluoro-n-propylvinylide (PPVE)/perfluoro-methyl Vinylether (PMVE) initiated by bis(perfluoro-2-n-propoxyethyl) diacyl peroxide were carried out. The homopolymers and copolymers obtained were characterized by19F and1H-NMR spectroscopy, DSC and TG. From the assignments of the characteristic signals, an interpretation of the polymer microstructures was provided and the presence of end groups arising from the radical initiator was suggested. CF3CF2CF2OCF(CF3)-was found to present in both PVDF and Poly(VDF-PPVE)(co)polymers, which was generated from the decomposition of the initiator. This radical enabled the assessment of the molecular weight of PVDF and Poly(VDF-PPVE)(co)polymers. PVDF polymerized from this initiator was shown to have better thermal stability than PVDF made from non-fluoro initiators. According to the Fine-Rss method, the reactivity ratiosfor both comonomers were rVDF～1.06. rppve～0.036and rVDF～1.33.rPMVE～0.032.