Method of producing finely divided polymer particles

DETAILED DESCRIPTION OF THE INVENTION In the aforementioned suspension polymerization method of the prior art, the viscosity of monomer droplets noticeably increases during the polymerizing procedure in which the monomer droplets (liquid) grow into polymer particles (solid), and this viscosity increase hinders smooth dispersion and coagulation of the droplets resulting in the formation of coarse, aggregated and non-uniform particles.
This problem is unavoidable in suspension polymerization.
On the contrary, in the method of the present invention, the size of the polymer solution droplets agitated and dispersed according to the above described process is determined after the dynamic equilibrium state for the dispersion-coagulation procedure of the polymer droplets has been established, depending on the concentration of the polymer solution, the ratio of the polymer solution to the aqueous medium, the kind and the amount of the dispersion stabilizer, the temperature, the agitation speed, the pH of the aqueous medium, etc.
The pH of the system is conveniently maintained at about 3 to about 11, even more preferably at 5 to 9.
The dynamic equilibrium is usually established in 10 to 20 minutes.
It should be noted that the viscosity of the liquid droplets during the dispersion procedure is determined by the solvent composition and remains constant, in clear contrast to the case of suspension polymerization wherein aggregation proceeds leading to a wide particle size distribution.
The present is characterized by an extremely uniform particle size.
Moreover, in an ordinary suspension polymerization, the reaction is completed in 4 to 15 hours, while the method of the present invention requires only 2 to 3 hours even when the time for dispersion and heating is taken into account.
Factors which determine particle size in the present invention are as follows: particle size increases with the concentration of the polymer solution, with the weight ratio of the polymer solution to the aqueous medium, and with the temperature of the aqueous medium, while it decreases with the amount of the dispersion stabilizer or the stabilizing aid, with the temperature of the polymer solution or with the speed of agitation