Ringpolümerisatsioon

Ringpolümerisatsioon, also known as ring-opening polymerization, is a type of chain-growth polymerization in which cyclic monomers undergo ring-opening to form a linear polymer chain. This process is distinct from condensation polymerization, where small molecules are eliminated during the reaction. The driving force for ring-opening polymerization is typically the release of ring strain present in the cyclic monomer. Common cyclic monomers include lactams, lactones, epoxides, and cyclic ethers.

There are several mechanisms by which ring-opening polymerization can occur. Cationic ring-opening polymerization is initiated by electrophiles, which attack the heteroatom in the ring, leading to ring opening and the formation of a carbocation. This carbocation then propagates the chain by attacking another monomer. Anionic ring-opening polymerization is initiated by nucleophiles, which attack an electrophilic carbon atom in the ring, creating an anionic chain end. Radical ring-opening polymerization involves radical species initiating the ring-opening process. Coordination polymerization, particularly for cyclic ethers and epoxides, often utilizes catalysts that coordinate to the monomer and facilitate ring opening.

Ring-opening polymerization is a versatile method for synthesizing a wide range of polymers with specific properties. For instance, lactams like caprolactam polymerize to form nylon-6, a widely used polyamide. Lactones can be polymerized to produce polyesters such as polylactic acid (PLA), a biodegradable and biocompatible material. Epoxides are polymerized to form polyethers, which find applications in polyurethanes and surfactants. The control over molecular weight and polymer architecture is often achievable in ring-opening polymerization, making it a valuable tool in polymer synthesis for various industrial and biomedical applications.