Molecular Weight Distribution of Fluorinated Polymers with Long Chain Branching

Abstract

The molecular weight distribution (MWD) of branched fluorinated terpolymers made of vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE) has been investigated. These polymers, as well as all VDF-based polymers, have trifunctional long chain branches originated by the transfer to polymer mechanism. Furthermore, one of the samples here examined has a certain amount of tetrafunctional long chain branches produced by copolymerizing the sample in the presence of a fluorinated diolefin. The MWD of the polymers has been evaluated by combining the size exclusion chromatography data with the intrinsic viscosity of the whole polymer. To highlight the effect of branching over the MWD, the polymer samples have been fractionated and the high molecular weight fractions have been analyzed. The reliability of the adopted approach has been assessed by comparing the obtained values of weight-average molecular weight with the ones measured by the laser light scattering technique.

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

“…In order to explain the bimodality of the MWD, they first used the homogeneous kinetic scheme already presented [39] and added chain transfer to polymer (CTP). The presence of this reaction was also proposed by Maccone et al [48] to explain the presence of long chain branching in a ter-polymer of 72 mol% of VDF, 18 mol% hexafluoropropylene (HFP), and 10 mol% tetrafluoroethylene (TFE). This hypothesis was confirmed by Saraf et al [40] by NMR analysis indicating the presence of CF 2 -CH 3 end groups.…”

Synthesis and physical properties of highly branched perfluorinated polymers from AB and AB2 monomers

“…The molecular weight of each polymer was measured using GPC, although there are several factors to take into account for the molecular weight measurements using this method for branched and fluorinated polymers: (a) GPC separates polymer chains by their hydrodynamic volume, but in the case of a branched polymer the same relationship as for linear standards between hydrodynamic volume and molecular weight does not exist because hydrodynamic volume also depends on the degree of branching . For branched polymers this will lead to underestimates in the molecular weight by gel permeation chromatography calibrated with linear standards; (b) fluorine content inherently affects retention volumes during GPC measurements.…”

“…The polymerization of fluorinated The molecular weight of each polymer was measured using GPC, although there are several factors to take into account for the molecular weight measurements using this method for branched and fluorinated polymers: (a) GPC separates polymer chains by their hydrodynamic volume, but in the case of a branched polymer the same relationship as for linear standards between hydrodynamic volume and molecular weight does not exist because hydrodynamic volume also depends on the degree of branching. 28 For branched polymers this will lead to underestimates in the molecular weight by gel permeation chromatography calibrated with linear standards; (b) fluorine content inherently affects retention volumes during GPC measurements. It has been demonstrated that increased fluorination leads to stronger aggregation in THF, which would lead to smaller hydrodynamic volumes, thus deflating molecular weight from GPC analysis calibrated with conventional PS standards; [29][30][31] (c) fluorinated polymers are inherently inert due to the low polarizability of the C-F bond.…”

Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics

“…This is a direct consequence of assumption (iv): since the polymer precipitates out of the sc phase, transfer to polymer cannot occur in that phase, the viscosity of the medium remains low and the termination rate constant can be considered length‐independent. On the contrary, the high polymer content in the pa‐phase enhances the role of chain transfer to polymer reactions,32 as well the effect of diffusion limitations on the reaction rate constants. For both phases, termination by combination only is considered because there is no evidence in the literature on disproportionation 17. The values of all homo‐ and cross‐termination rate constants have been assumed equal.…”

“…This is a direct consequence of assumption (iv): since the polymer precipitates out of the sc phase, transfer to polymer cannot occur in that phase, the viscosity of the medium remains low and the termination rate constant can be considered length‐independent. On the contrary, the high polymer content in the pa‐phase enhances the role of chain transfer to polymer reactions,32 as well the effect of diffusion limitations on the reaction rate constants.…”