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Formation of Polymer Micropowder Using Supercritical Carbon Dioxide as a Solvent


- To a New Process of Non Solvent Polymerization -

National Institute of Materials and Chemical Research
Takeshi Sako, Ph.D
Katsuto Ohtake, Ph.D
NOF Corporation, Corporate R&D
Katsunobu Mizuguchi, Ph.D
to Japanese

Up to this time, polymer micropowder has been obtained by solvent-removing, desiccating　and crushing the polymers which are produced by the different polimerization methods such as bulk, solution, suspension and emulsion polimerizations. However, the treatment of solvents used especially for solution, suspension and emulsion polimerization processes has been a serious problem for some time.
The technique developed by our group is to synthesize a micropowder polymer in a single step by using supercritical carbon dioxide in place of H2O or organic solvents.
The micropowder obtained by this technique can be used directly in the process of manufacturing powder paints, inks, adhesive agents, plastic substances and medical supplies. The most significant characteristics of this technique are:

@ free of organic solvents hazardous to environment
A possibility of producing polymer micropowder directly usable for industrial process in one step formation.

When this technique shall be made practicable, it will be an environmentally friendly alternative industrial process of micropowder formation by polymerization in supercritical carbon dioxide without using organic solvents. The organic solvent is one of the chemical sources causing photochemical smog along with hydrocarbon contained in the automotive emission gas of which the emission regulation is tightened strictly in the European countries and the US.

The two main points in the results of the technique that we developed are as follows:

(1) Poly(heptadecafluorodecyl acrylate) and poly(heptadecaluorodecyl methacrylate) which contain special perfluoroalkyl side chains were used as polymeric surfactants in supercritical carbon dioxide. As a result, the method for synthesizing regular diameter spherical polymer micropowder in one step was proven successfully for the first time in Japan.

(2) Using the surfactants such as perfluoroalkyls mentioned in (1) is an expensive process. However, in the course of this study, we found a technique for dispersion polimerization by simply applying widely used monomers such as acid monomers (eg. acrylic acid and methacrylic acid) as an alternative surfactant. Although the spheres do not come out as regular as in the previous process in (1), we could obtain polymer micropowder smaller than the powder formed by a crushing method.

2a-photo
Methyl methacrylate polimerization formation
(Polyheptadecafluorodecyl acrylate was used as a surfactant)


2b-photo　　　　2c-photo
Methyl methacrylate/methacrylic acid co-polymer formation
The result of this research was obtained in the course of technical guidance given to NOF Corporation by our Institute since June, l998.

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