In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains [1] [2] [3]. Polymer chemistry or macromolecular chemistry is a multidisciplinary Science that deals with the Chemical synthesis and chemical properties of A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds There are many forms of polymerization and different systems exist to categorize them.
The main categories are
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Introduction
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Single-monomer formed polymers
Co-polymers
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In chemical compounds, polymerization occurs via a variety of reaction mechanisms which vary in complexity due to functional groups present in reacting compounds[4] and their inherent steric effects explained by VSEPR Theory. Addition polymerisation, also called polyaddition or chain growth polymerization, is a Polymerisation technique where unsaturated Monomer Step-growth polymerization is a Polymerization process that involves a Chemical reaction between multifunctional Monomer molecules In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions See also Intramolecular forces ' Steric effects arise from the fact that each Atom within a Molecule occupies a certain Valence shell electron pair repulsion (VSEPR theory (1957 is a model in Chemistry, which is used for predicting the shapes of individual Molecules based In more straightforward polymerization, alkenes, which are a relatively stable due to σ bonding between carbon atoms form polymers through relatively simple radical reactions; conversely, more complex reactions such as those that involve substitution at the carbonyl atom require more complex synthesis due to the way in which reacting molecules polymerize. In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic [4]
As alkenes can be formed in somewhat straightforward reaction mechanisms, they form useful compounds such as polyethylene and polyvinyl chloride (PVC) when undergoing radical reactions,[4] which are produced in high tonnages each year[4] due to their usefulness in manufacturing processes of commercial products, such as piping, insulation and packaging. Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Polymers such as PVC are generally referred to as "singular" polymers as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one molecule are referred to as "co-polymers".
Other monomer units, such as formaldehyde hydrates or simple aldehydes, are able to polymerize themselves at quite low temperatures (>-80oC) to form trimers;[4] molecules consisting of 3 monomer units which can cyclize to form ring cyclic structures, or undergo further reactions to form tetramers,[4] or 4 monomer-unit compounds. A tetramer is a Protein with four subunits (tetrameric There are homo-tetramers (all Subunits are identical such as Glutathione S-transferase or Further compounds either being referred to as oligomers[4] in smaller molecules. In Chemistry, an oligomer consists of a limited number of Monomer units (ολιγος or oligos is Greek for "a few" in contrast to a Generally, because formaldehyde is an exceptionally reactive electrophile it allows nucleophillic addition of hemiacetal intermediates, which are generally short lived and relatively unstable "mid stage" compounds which react with other molecules present to form more stable polymeric compounds. In Chemistry, a nucleophile (literally nucleus lover as in nucleus and phile) is a Reagent that forms a Chemical bond to
Polymerization that is not sufficiently moderated and proceeds at an undesirably fast rate can be very hazardous. This phenomenon is known as Hazardous polymerization and can cause fires and explosions. Radical polymerization of pure Styrene causes the Viscosity to increase
Chain-growth
Chain-growth polymerization or addition polymerization involves the linking together of molecules incorporating double or triple chemical bonds. Addition polymerisation, also called polyaddition or chain growth polymerization, is a Polymerisation technique where unsaturated Monomer A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic These unsaturated monomers (the identical molecules which make up the polymers) have extra internal bonds which are able to break and link up with other monomers to form the repeating chain. Addition polymerization is involved in the manufacture of polymers such as polyethylene, polypropylene and polyvinyl chloride (PVC). Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Polypropylene or polypropene ( PP) is a Thermoplastic Polymer, made by the Chemical industry and used in a wide variety of applications A special case of addition polymerization leads to living polymerization. In Polymer chemistry, living polymerization is a form of Addition polymerization where the ability of a growing Polymer chain to terminate has
In the polymerization of ethylene, its pi bond is broken and these two electrons rearrange to create a new propagating center like the one that attacked it. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. The form this propagating center takes depends on the specific type of addition mechanism. There are several mechanisms through which this can be initiated. The free radical mechanism was one of the first methods to be used. In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell Free radicals are very reactive atoms or molecules which have unpaired electrons. Taking the polymerization of ethylene as an example, the free radical mechanism can be divided in to three stages: chain initiation, chain propagation and chain termination. Addition polymerisation, also called polyaddition or chain growth polymerization, is a Polymerisation technique where unsaturated Monomer Chain propagation is a process in which a Reactive intermediate is continuously regenerated during the course of a Chemical reaction. Chain termination is any Chemical reaction leading to the destruction of a Reactive intermediate in a Chain propagation step in the course of a
Free radical addition polymerization of ethylene must take place at high temperatures and pressures, approximately 300°C and 2000 At. Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. While most other free radical polymerizations do not require such extreme temperatures and pressures, they do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains. A newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst especially with respect to polymer branching. A Ziegler-Natta catalyst is a Reagent or a mixture of reagents used in the production of Polymers of 1-alkenes (α-olefins Polymer chemistry, branching occurs by the replacement of a Substituent, e
Other forms of addition polymerization include cationic addition polymerization and anionic addition polymerization. An anionic addition polymerization of Vinyl Monomers is an Addition polymerization initiated by a strong base and Anion, such as an While not used to a large extent in industry yet due to stringent reaction conditions such as lack of water and oxygen, these methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such as polypropylene. Polypropylene or polypropene ( PP) is a Thermoplastic Polymer, made by the Chemical industry and used in a wide variety of applications Cationic and anionic mechanisms are also more ideally suited for living polymerizations, although free radical living polymerizations have also been developed. In Polymer chemistry, living polymerization is a form of Addition polymerization where the ability of a growing Polymer chain to terminate has
Step-growth
Step growth polymers are defined as polymers formed by the stepwise reaction between functional groups of monomers. Step-growth polymerization is a Polymerization process that involves a Chemical reaction between multifunctional Monomer molecules Most step growth polymers are also classified as condensation polymers, but not all step growth polymers (like polyurethanes formed from isocyanate and alcohol bifunctional monomers) release condensates. A polyurethane, commonly abbreviated PU, is any Polymer consisting of a chain of organic units joined by urethane links Isocyanate is the Functional group of atoms &ndashN=C=O (1 Nitrogen, 1 Carbon, 1 Oxygen) not to be confused with the Cyanate Step growth polymers increase in molecular weight at a very slow rate at lower conversions and only reach moderately high molecular weights at very high conversion (i. e. >95%).
To alleviate inconsistencies in these naming methods, adjusted definitions for condensation and addition polymers have been developed. A condensation polymer is defined as a polymer that involves elimination of small molecules during its synthesis, or contains functional groups as part of its backbone chain, or its repeat unit does not contain all the atoms present in the hypothetical monomer to which it can be degraded. An elimination reaction is a type of Organic reaction in which two Substituents are removed from a molecule in either a one or two-step mechanism. In Organic chemistry, the backbone chain of a Polymer is the series of Covalently bonded Atoms that together create the continuous chain of the In Polymer chemistry, a structural unit is a building block of a Polymer chain and related to the Repeat unit.
See also
References
- ^ Introduction to Polymers 1987 R. Plasma polymerization uses Plasma sources to generate a Gas discharge that provides energy to activate or fragment gaseous or liquid Monomer, A Ziegler-Natta catalyst is a Reagent or a mixture of reagents used in the production of Polymers of 1-alkenes (α-olefins A metallocene is a compound with the general formula (C5R52M consisting of two cyclopentadienyl anions (Cp bound to a metal center in the oxidation J. Young Chapman & Hall ISBN 0-412-22170-5
- ^ International Union of Pure and Applied Chemistry, et al. (2000) "IUPAC Gold Book" Retrieved on 11 May 2007 from "IUPAC Gold Book" on http://goldbook.iupac.org/
- ^ Clayden, J. Events 330 - Byzantium is renamed ''Nova Roma'' during a dedication ceremony but is more popularly referred to as Constantinople Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. , Greeves, N. et al. (2000). "Organic chemistry" Oxford
- ^ a b c d e f g Clayden, J. , Greeves, N. et al. (2000), p1450-1466
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