Polyolefin in Water

Emulsion polymerization is usually restricted to radical chemistry. Only a handful of examples of aqueous anionic, cationic and catalytic polymerizations are known. This is due of the reactivity of water toward anions, cations and metal-carbon bonds (and metal-oxygen bonds). One of the problem that we have been interested for 4 years now is the possibility to catalytically polymerize olefins in water. Polyolefins, such as polyethylene, and polypropylene are commodity plastics prepared on a huge scale (200 billion pounds per year). We envision that the possibility of preparing polyolefins dispersed into water could open the door to a large variety of novel materials.

1. A very nice catalyst (details)

We stumbled on a very nice catalyst that has activities over 2,000,000g/g/h in organic media. This catalyst is a neutral ketophosphoylide Ni(II) catalyst related to the family of Shop oligomerization catalysts prepared by Professor Keim in Germany.

2. Polymerization in water
Using this catalyst, it is possible to polymerize ethylene in water. As the reaction occurs in aqueous medium, the catalyst activity is very much lower than in organic medium. Activities as high as several 104 g/g/h can be obtained (P = 20 bars, T = 55 C). Even in the presence of surfactant, the product we form is not colloidaly stable in water. Here is the picture of a HDPE latex that is not colloidaly stable :

Using a miniemulsion process, it is however possible to gain in stability and to generate a very nice and stable latex. On the right you see the picture of a HDPE latex prepared by this process, and the left you see the transmission electronic microscopy picture of some of the particles of this latex. Note how irregular the particles are : this is due to the very high crystallinity of the HDPE. We have been the first ones to synthesize this type of latex … well, maybe the second ones : this issue is in debate between us and our competitor (and friend), Dr Stefan Mecking, of Germany.

3. Copolymerization in water
Several monomers, polar and non polar, have been copolymerized with ethylene. Comonomer insertion breaks the crystallinity of the polymer. The particles are no more irregular and crystalline, they are spherical and sticky (a good thing to make a coating or an adhesive). The latex made by copolymerization is very stable (even more than the HDPE one). On the right a 30% solids latex of PE-co-hexadecene. Due to the specific confinement of the reaction into nanoreactors (a phenomenon usually referred as compartmentalization), the copolymerization is easier to carry out than in a typical solution polymerization

4. And now, a nice application ….

The PE Team :
Many thanks to Remi Soula, Benjamin Saillard, Atanas Tomov, Roger Spitz and Xavier Drujon ! Financial support from Atofina.