Graft polymer

Graft polymers are segmented copolymers with a linear backbone of one composite and randomly distributed branches of another composite. The picture labeled 'graft polymer' shows how grafted chains of species B are covalently bonded to polymer species A. Although the side chains are structurally distinct from the main chain, the individual grafted chains may be homopolymers or copolymers.Graft polymers have been synthesized for many decades and are especially used as impact resistant materials, thermoplastic elastomers, compatibilizers, or emulsifiers for the preparation of stable blends or alloys. One of the more well known examples of a graft polymer is high impact polystyrene, which consists of a polystyrene backbone with polybutadiene grafted chains. Graft copolymers are a branched copolymer where the components of the side chain are structurally different than that of the main chain. Graft copolymers containing a larger quantity of side chains are capable of wormlike conformation, compact molecular dimension, and notable chain end effects due to their confined and tight fit structures.The preparation of graft copolymers has been around for decades. All synthesis methods can be employed to create general physical properties of graft copolymers. They can be used for materials that are impact resistant, and are often used as thermoplastics elastomers, compatibilizers or emulsifiers for the preparation of stable blends or alloys. Generally, grafting methods for copolymer synthesis results in materials that are more thermostable than their homopolymer counterparts.There are three methods of synthesis, grafting to, grafting from, and grafting through, that are used to construct a graft polymer. There are many different approaches to synthesizing graft copolymers. Usually they employ familiar polymerization techniques that are commonly used such as atom transfer radical polymerization (ATRP), ring-opening metathesis polymerization (ROMP), anionic and cationic polymerizations, and free radical living polymerization. Some other less common polymerization include radiation-induced polymerization, ring-opening olefin metathesis polymerization, polycondensation reactions, and iniferter-induced polymerization. The grafting to method involves the use of a backbone chain with functional groups A that are distributed randomly along the chain. The formation of the graft copolymer originates from the coupling reaction between the functional backbone and the end-groups of the branches that are reactive. These coupling reactions are made possible by modifying the backbone chemically. Common reaction mechanisms used to synthesize these copolymers include free-radical polymerization, anionic polymerization, atom-transfer radical-polymerization, and living polymerization techniques. Copolymers that are prepared with the grafting-to method often utilize anionic polymerization techniques. This method uses a coupling reaction of the electrophilic groups of the backbone polymer and the propagation site of an anionic living polymer. This method would not be possible without the generation of a backbone polymer that has reactive groups. This method has become more popular with the rise of click chemistry. A high yield chemical reaction called atom transfer nitroxide radical coupling chemistry is for the grafting-to method for polymerization. In the grafting-from method, the macromolecular backbone is chemically modified in order to introduce active sites capable of initiating functionality. The initiating sites can be incorporated by copolymerization, can be incorporated in a post-polymerization reaction, or can already be a part of the polymer. If the number of active sites along the backbone participates in the formation of one branch, then the number of chains grafted to the macromolecule can be controlled by the number of active sites. Even though the number of grafted chains can be controlled, there may be a difference in the lengths of each grafted chain due to kinetic and steric hindrance effects. Grafting from reactions have been conducted from polyethylene, polyvinylchloride, and polyisobutylene. Different techniques such as anionic grafting, cationic grafting, atom-transfer radical polymerization, and free-radical polymerization have been used in the synthesis of grafting from copolymers.