2 - Solution radical polymerization

Abstract

Radical polymerization is one of the most versatile and widely applied techniques. It can generally be categorized into two types: free-radical polymerization (FRP) and controlled/living radical polymerization (CLRP). FRP enables the synthesis of high-molecular-weight polymers from a variety of monomers. FRP is a key synthesis route for obtaining a wide variety of different polymers and material composites. Acrylates and methacrylates are among the most commonly used monomers in FRP. CLRP produces well-defined (co)polymers with predetermined molecular weight, controllable polydispersity, and preserved chain-end functionality. Generally, chemically grafting techniques include the “grafting to” and “grafting from” methods used to prepare modified polymers or copolymers by CLRPs. PEGylation is a common process used to improve the therapeutic value of a medicine by prolonging its body residence time. It involves the attachment of one or more poly(ethylene glycol) (PEG) chains on the entity and can be applied to various (bio)polymers, small molecules, and cells. The intermolecular crosslinking is the key reaction for the control of gelation as the formation of three-dimensional network of indefinitely large size, whereas the key reaction for controlling the network structure is the intramolecular crosslinking that leads to the formation of multiple crosslinks generating the net structure of the network polymer. When two or more different monomers unite together to polymerize, the product is called a statistical, alternating or block copolymer. FRP has been used in material research as well, such as in the functionalization of various compounds such as carbon nanotubes (CNTs) and dots, clays, inorganic particles, etc. Chain-growth polymerization (“grafting to”) synthesizes a polymer with predetermined properties. Conversely “grafting from,” with radical polymerization techniques such as atom transfer radical polymerization (ATRP) or nitroxide-mediated polymerization (NMP), allows rapid growth of high-molecular-weight polymer composites. Among the conventional water-soluble polymers, polyacrylamide, poly-N-isopropylacrylamide (PNIPAM), etc. and their analogs and copolymers with very high molecular weights, thermosensitivity, drug delivery activities, etc. have gained more and more technical importance for use in many fields. The carbohydrate-based polymers and the copolymers prepared by CLRP are well studied for their gene delivery efficacies and are found to be excellent materials with decreased toxicity as well as enhanced gene expression.