Term: Polymerization
**Polymerization:**
– Different forms of polymerization exist, categorized based on reaction mechanisms and functional groups according to IUPAC.
– Alkenes form polymers through radical reactions.
– High tonnages of polymers like polyethylene and PVC are produced annually.
– Homopolymers consist of repeated monomer units, while copolymers consist of more than one monomer unit.
**Step-growth vs. Chain-growth Polymerization:**
– Step-growth and chain-growth are main classes of polymerization mechanisms.
– Step-growth requires precise stoichiometry control.
– Chain-growth yields high molecular-weight polymers but applies to specific monomers.
– Step-growth involves pairs of reactants combining to form longer polymer molecules.
– Chain-growth involves rapid chain propagation by adding monomers to a growing chain.
**Step-growth Polymerization:**
– Step-growth polymers are formed by independent reaction steps between monomer units.
– Most step-growth polymers are condensation polymers.
– Step-growth polymers increase in molecular weight slowly at lower conversions.
– Examples include polyesters and solid-state polymerization for polyamides.
– Polyurethanes are step-growth polymers formed without the loss of water.
**Chain-growth Polymerization:**
– Chain-growth involves adding monomers to a growing chain with an active center.
– Long chains are formed from the beginning of the reaction.
– Chain-growth polymerization is used in manufacturing polymers like polyethylene and PVC.
– Other forms include cationic and anionic addition polymerization.
– Ziegler–Natta polymerization allows control of polymer branching.
**Photopolymerization:**
– Photopolymerization reactions are initiated by visible or ultraviolet light.
– Photopolymerization can be chain-growth or step-growth.
– Light absorption triggers addition or condensation reactions in step-growth photopolymerization.
– Photopolymerization is used in 3D printing processes.
– Multiphoton polymerization enables the fabrication of complex structures.
**Polymer Chemistry:**
– Various references and studies in polymer chemistry from different sources and authors.
– Covers contemporary polymer chemistry, polymer science, technology, and specific studies on controlled radical polymerization and methods for polymer fabrication.
In polymer chemistry, polymerization (American English), or polymerisation (British English), 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 chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the functional groups present in the reactants and their inherent steric effects. In more straightforward polymerizations, alkenes form polymers through relatively simple radical reactions; in contrast, reactions involving substitution at a carbonyl group require more complex synthesis due to the way in which reactants polymerize.
As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as polyethylene and polyvinyl chloride (PVC), which are produced in high tonnages each year due to their usefulness in manufacturing processes of commercial products, such as piping, insulation and packaging. In general, polymers such as PVC are referred to as "homopolymers", as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one monomer unit are referred to as copolymers (or co-polymers).
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Homopolymers
Copolymers
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Other monomer units, such as formaldehyde hydrates or simple aldehydes, are able to polymerize themselves at quite low temperatures (ca. −80 °C) to form trimers; molecules consisting of 3 monomer units, which can cyclize to form ring cyclic structures, or undergo further reactions to form tetramers, or 4 monomer-unit compounds. Such small polymers are referred to as oligomers. Generally, because formaldehyde is an exceptionally reactive electrophile it allows nucleophilic addition of hemiacetal intermediates, which are in general short-lived and relatively unstable "mid-stage" compounds that react with other non-polar molecules present to form more stable polymeric compounds.
Polymerization that is not sufficiently moderated and proceeds at a fast rate can be very hazardous. This phenomenon is known as autoacceleration, and can cause fires and explosions.