Selective Crosslinking of FKM for Optimized Properties

Fluoroelastomers are well-known for their excellent properties concerning chemical, thermal stability and inertness to acids, bases, solvents and oils.  They are synthesized from a variety of monomers such as vinylidene fluoride (VF­₂), hexafluoropropylene (HFP), Tetrafluoroethylene (TFE), etc¹.

One such fluorocarbon elastomer is the VF₂/HFP copolymer, which exhibits unique mechanical properties after crosslinking with hexafluoroisopropylidene-bis(4-hydroxy benzene (Bisphenol AF or BPAF).

The mechanism of crosslinking of VF₂/HFP copolymers with BPAF has been investigated and explained by various authors in a semi-quantitative way.

In this paper we characterized the crosslinking reaction as well as the some characteristic physical properties as a function of the relevant compound ingredients.

As a result we created a system which allows for the prediction of the vulcanization properties as well as the properties of the vulcanizate.  The basis is a model which predicts the amount of mechanically active crosslinks as a function of the VF₂/HFP copolymer (Levatherm F6623 with a fluoro content of 66wt%), the crosslinking agent BPAF, the phase transfer catalyst benzyl­triphenyl­phosphonium chloride (PC), the acid receptor Ca(OH)₂ and the cure activator MgO.

For a practical and easy to use application the model was extended to the ‘so called’ masterbatches FC20 and FC30 which contain the crosslink agent and the phase transfer catalyst PC.  The desired vulcanization and vulcanizate properties can therefore be achieved by a specific combination of the masterbatches with the VF₂/HFP copolymer (F6623).