Continuous Precipitation Polymerization of Vinylidene Fluoride in Supercritical Carbon Dioxide:  Formation of Polymers with Bimodal Molecular Weight Distributions

Abstract

The polymerization of vinylidene fluoride in supercritical carbon dioxide was studied in a continuous stirred tank reactor using diethylperoxydicarbonate as the free radical initiator. Experiments were carried out to investigate the effect of inlet monomer concentration, temperature, average residence time, and agitation on the polymerization rate, the average molecular weights, and the molecular weight distribution of the poly(vinylidene fluoride). A homogeneous kinetic model that includes inhibition due to chain transfer to monomer predicted the polymerization rates reasonably well. However, imperfect mixing, rather than a chemical effect, may have caused the apparent inhibition observed at high monomer concentrations. At inlet monomer concentrations greater than about 1.5 M, broad and bimodal molecular weight distributions were observed. An extended homogeneous kinetic model that includes chain transfer to polymer predicted the polydispersities reasonably well. This model also predicted a region of inoperability that matched the experimental results. However, the extended homogeneous model could not account for the bimodal distributions.

Mixed substituent poly[(vinyloxy)cyclotriphosphazenes]

“…13 Chain transfer has been observed in the polymerization of fluorine containing organic monomers such as vinylidene fluoride. 17 However, the trifluorethoxy substituted cyclophosphazene monomers N 3 P 3 (OCH 2 C-F 3 ) 5 20 have been shown to successfully undergo radical initiated polymerization so other factors need to be examined. We have previously established, using UPS and NMR spectroscopy, that nature of the olefin in the series N 3 P 3 X 5 OCH¼ ¼CH 2 (X ¼ F, Cl, OCH 2 CF 3 , OCH 3 ,NMe 2 ) is controlled by the substituent X progressing from a vinyl acetate like center with halogen substituents to a vinyl ether like center for the dimethylamino derivative.…”

The Synthesis and Crystallization of Poly(vinylidene fluoride) in Supercritical CO2

“…DeSimone and Howdle have reported independently that the increased reaction pressure increases the molecular weight and polydispersity of PVDF polymerized in sc-CO 2 by both the continuous process and the batch process [13,[27][28] . The reason might be proposed as following: the activation volume is negative during the polymerization reaction of VDF in sc-CO 2 according to the transition-state theory [29,30].…”

“…Then, they reported the continuous precipitation polymerization of vinylidene fluoride (VDF) in sc-CO 2 [12,13]. They set up an extended homogeneous kinetic model predicting the polydispersities of PVDF reasonably well [10].…”

Polymerization of Vinylidene Difluoride in Supercritical Carbon Dioxide

“…In agreement with such a scheme, homopolymerization of VDF in sc-CO 2 was shown to be of the precipitation polymerization type [51 -53], characterized by multimodal molecular weight distributions, low powder density [51, 53 -55] and the presence of an -virtually erratic -inhibition period at the beginning of the polymerizations [53,55]. In spite of this tedious reaction kinetics, successful attempts to set up continuous polymerization reactor systems have been published [56 -58].…”