Ioonpolümerisatsioonid

Ioonpolümerisatsioonid are a type of chain-growth polymerization where the propagating species is an ion. This ionic species can be either a carbocation, leading to cationic polymerization, or a carbanion, leading to anionic polymerization. These processes are initiated by compounds that can generate ions, typically strong acids or bases, or by compounds that can form ions upon reaction with a catalyst.

Cationic polymerization is usually initiated by strong Lewis acids like BF3, AlCl3, or SnCl4, often in the presence of a co-initiator such as water or an alcohol. The propagating species is a carbocation, and the reaction proceeds rapidly, often at low temperatures. Monomers that can stabilize a positive charge, such as isobutylene and styrene, are readily polymerized cationically.

Anionic polymerization is initiated by strong bases or nucleophiles, such as organometallic compounds (e.g., alkyllithiums) or alkali metal amides. The propagating species is a carbanion. Monomers with electron-withdrawing groups, like vinyl chloride, acrylonitrile, and butadiene, are typically polymerized anionically. Anionic polymerization can often be controlled to produce polymers with specific molecular weights and narrow molecular weight distributions, a process known as living polymerization. The choice between cationic and anionic polymerization depends heavily on the structure of the monomer and the desired polymer properties.