In polymer chemistry, polymerization, or polymerisation, is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them.
In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar. Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.
In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer. The reactive center can be radical, anionic or cationic. Some cyclic monomers such as norbornene or cyclooctadiene can be polymerized to high molecular weight polymers by using metal catalysts. ROP is a versatile method for the synthesis of biopolymers.
Polythiophenes (PTs) are polymerized thiophenes, a sulfur heterocycle. The parent PT is an insoluble colored solid with the formula (C4H2S)n. The rings are linked through the 2- and 5-positions. Poly(alkylthiophene)s have alkyl substituents at the 3- or 4-position(s). They are also colored solids, but tend to be soluble in organic solvents.
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are sometimes called bipolymers. Those obtained from three and four monomers are called terpolymers and quaterpolymers, respectively. Copolymers can be characterized by a variety of techniques such as NMR spectroscopy and size-exclusion chromatography to determine the molecular size, weight, properties, and composition of the material.
In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Initiation creates a reactive centre on a molecule which produces a chain reaction. The reactive centre generated by initiation is usually a radical, but can also be cations or anions. Once the reaction is initiated, the species goes through propagation where the reactive species reacts with stable molecules, producing stable species and reactive species. This process can produce very long chains of molecules called polymers, which are the building blocks for many materials. After propagation, the reaction is then terminated. There are different types of initiation, with the two main ways being thermal initiation and photo-initiation (light).
Chain-growth polymerization (AE) or chain-growth polymerisation (BE) is a polymerization technique where unsaturated monomer molecules add onto the active site on a growing polymer chain one at a time. There are a limited number of these active sites at any moment during the polymerization which gives this method its key characteristics.
Atom transfer radical polymerization (ATRP) is an example of a reversible-deactivation radical polymerization. Like its counterpart, ATRA, or atom transfer radical addition, ATRP is a means of forming a carbon-carbon bond with a transition metal catalyst. Polymerization from this method is called atom transfer radical addition polymerization (ATRAP). As the name implies, the atom transfer step is crucial in the reaction responsible for uniform polymer chain growth. ATRP was independently discovered by Mitsuo Sawamoto and by Krzysztof Matyjaszewski and Jin-Shan Wang in 1995.
Reversible addition−fragmentation chain-transfer or RAFT polymerization is one of several kinds of reversible-deactivation radical polymerization. It makes use of a chain-transfer agent (CTA) in the form of a thiocarbonylthio compound to afford control over the generated molecular weight and polydispersity during a free-radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia in 1998, RAFT polymerization is one of several living or controlled radical polymerization techniques, others being atom transfer radical polymerization (ATRP) and nitroxide-mediated polymerization (NMP), etc. RAFT polymerization uses thiocarbonylthio compounds, such as dithioesters, thiocarbamates, and xanthates, to mediate the polymerization via a reversible chain-transfer process. As with other controlled radical polymerization techniques, RAFT polymerizations can be performed under conditions that favor low dispersity and a pre-chosen molecular weight. RAFT polymerization can be used to design polymers of complex architectures, such as linear block copolymers, comb-like, star, brush polymers, dendrimers and cross-linked networks.
Catalytic chain transfer (CCT) is a process that can be incorporated into radical polymerization to obtain greater control over the resulting products.
Living free radical polymerization is a type of living polymerization where the active polymer chain end is a free radical. Several methods exist. IUPAC recommends to use the term "reversible-deactivation radical polymerization" instead of "living free radical polymerization", though the two terms are not synonymous.
Polyfluorene is a polymer with formula (C13H8)n, consisting of fluorene units linked in a linear chain — specifically, at carbon atoms 2 and 7 in the standard fluorene numbering. It can also be described as a chain of benzene rings linked in para positions with an extra methylene bridge connecting every pair of rings.
Conjugated microporous polymers (CMPs) are a sub-class of porous materials that are related to structures such as zeolites, metal-organic frameworks, and covalent organic frameworks, but are amorphous in nature, rather than crystalline. CMPs are also a sub-class of conjugated polymers and possess many of the same properties such as conductivity, mechanical rigidity, and insolubility. CMPs are created through the linking of building blocks in a π-conjugated fashion and possess 3-D networks. Conjugation extends through the system of CMPs and lends conductive properties to CMPs. Building blocks of CMPs are attractive in that the blocks possess broad diversity in the π units that can be used and allow for tuning and optimization of the skeleton and subsequently the properties of CMPs. Most building blocks have rigid components such as alkynes that cause the microporosity. CMPs have applications in gas storage, heterogeneous catalysis, light emitting, light harvesting, and electric energy storage.
Reversible deactivation radical polymerizations (RDRPs) are members of the class of reversible deactivation polymerizations which exhibit much of the character of living polymerizations, but cannot be categorized as such as they are not without chain transfer or chain termination reactions. Several different names have been used in literature, which are:
A sequence-controlled polymer is a macromolecule, in which the sequence of monomers is controlled to some degree. This control can be absolute but not necessarily. In other words, a sequence-controlled polymer can be uniform or non-uniform (Ð>1). For example, an alternating copolymer synthesized by radical polymerization is a sequence-controlled polymer, even if it is also a non-uniform polymer, in which chains have different chain-lengths and slightly different compositions. A biopolymer with a perfectly-defined primary structure is also a sequence-controlled polymer. However, in the case of uniform macromolecules, the term sequence-defined polymer can also be used.
In polymer chemistry, 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 better-known examples of a graft polymer is a component used in high impact polystyrene, consisting of a polystyrene backbone with polybutadiene grafted chains.
Interfacial polymerization is a type of step-growth polymerization in which polymerization occurs at the interface between two immiscible phases, resulting in a polymer that is constrained to the interface. There are several variations of interfacial polymerization, which result in several types of polymer topologies, such as ultra-thin films, nanocapsules, and nanofibers, to name just a few.
Copper-based reversible-deactivation radical polymerization(Cu-based RDRP) is a member of the class of reversible-deactivation radical polymerization. In this system, various copper species are employed as the transition-metal catalyst for reversible activation/deactivation of the propagating chains responsible for uniform polymer chain growth.
Functionalized polyolefins are olefin polymers with polar and nonpolar functionalities attached onto the polymer backbone. There has been an increased interest in functionalizing polyolefins due to their increased usage in everyday life. Polyolefins are virtually ubiquitous in everyday life, from consumer food packaging to biomedical applications; therefore, efforts must be made to study catalytic pathways towards the attachment of various functional groups onto polyolefins in order to affect the material's physical properties.
Anne J. McNeil is an American chemist who currently works at the University of Michigan, where she holds the position of Arthur F. Thurnau Professor of Chemistry and Macromolecular Science and Engineering. In 2017, McNeil was named a fellow of the American Association for the Advancement of Science (AAAS).
