Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: molecular weight distribution

Abstract

The surfactant‐free precipitation polymerization of vinylidene fluoride (VF2) in supercritical carbon dioxide was studied in a continuous stirred autoclave. The polymerization temperature ranged from 65 to 85°C, the average residence time in the reactor varied from 10 to 50 min., and the pressure was between 210 and 305 bar. Diethyl peroxydicarbonate was used as the initiator. The fractional conversion of monomer varied from 7 to 26%, the number‐average molecular weight of the polymer was between about 14,000 and 79,000, and the weight‐average molecular weight was between about 21,000 and 700,000. In many cases, the polymer exhibited a bimodal molecular‐weight distribution, especially at high monomer concentrations.

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].…”

Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: modeling the molecular weight distribution

“…Second, the possible occurrence of chain transfer to polymer has been ignored. However, the uncertainty in the experimental MWDs for PVDF also may contribute to the differences between the model and the data (Saraf, 2001).…”

Reaction engineering of the emulsion homopolymerization of vinylidene fluoride: Progress and challenges

“…In subsequent papers, the same group analyzed the effect of the reaction conditions on the average molecular weights. Specifically, they investigated the impact of the inlet monomer concentration, the residence time, the agitation rate, and the temperature.…”

“…One factor that can help to elucidate the reactive sites of the polymerization is the equilibrium sorption of VDF/CO2/PVDF. Some studies showed that the concentration of VDF in PVDF is very low in the presence of scCO 2 (P < 100 bar), therefore very low rate polymerization in polymer phases can be expected, which justifies the choice of using a one‐phase reaction.…”