| Abstract: | Crystallization processes occurring during polymer synthesis in a nonsolvent medium are discussed. It is concluded that in the case of heterogeneous polymerization of ethylene the polymer is produced as a supercooled liquid surrounding the catalyst particles. These particles then coalesce until a critical size is reached allowing a high nucleation probability. Thus coalescence coupled with polymerization, leads to crystallization at a relatively uniform particle size. Two less usual polymerization catalyst systems, VCl3 produced by a high-frequency discharge in VCl4 vapor, and the mixture of TiCl4 and Al(CH3)3 vapors (an apparently homogeneous system) are used to illustrate these concepts for polyethylene. |
