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Polymerization Reactors
Published in James J. Carberry, Arvind Varma, Chemical Reaction and Reactor Engineering, 2020
Matthew Tirrell, Rafael Galvan, Robert L. Laurence
Not a great deal of literature is available on reactor design for nonlinear step-growth polymerization. Two factors probably account for this. One is that nonlinear step-growth polymers have never been produced in very large volumes. The other is that many of these materials are thermosetting materials, neither soluble nor fusible once made, so that the “reactor” is frequently simply a mold of the desired shape. Examples of important nonlinear step-growth polymerizations include phenolic resin manufacture, ureaformaldehyde resin manufacture, epoxies, and many polyurethanes.
Polymers
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Kiran Meghwal, Gunjan Kashyap, Rakshit Ameta
Polymer is a large molecule or macromolecule, composed of many repeating subunits. Because of their broad range of properties, both synthetic and natural polymers play an essential and ubiquitous role in day-to-day life. Polymers range from familiar synthetic plastics to natural biopolymers (DNA and proteins) that are fundamental to the biological structure and function. Polymers (natural and synthetic) are formed via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecules produces unique physical properties, including toughness, viscoelasticity and a tendency to form glasses and semicrystalline structures rather than crystals. Polymerization is the process of combining many small molecules (monomers) into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. Synthetic methods are generally divided into two categories: step-growth polymerization and chain-growth polymerization. The essential difference between the two is that in chain-growth polymerization, monomers are added to the chain one at a time only, as in polyethylene, whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester. Synthetic polymerization reactions may be carried out with or without a catalyst.
Introduction to Polymerization
Published in F. Joseph Schurk, Pradeep B. Deshpande, Kenneth W. leffew, Vikas M. Nadkarni, Control of Polymerization Reactors, 2017
Schurk F. Joseph, Deshpande Pradeep B.
Step-growth polymerization involves reaction of functional groups on adjacent monomer molecules with the evolution of water or other low-molecular-weight by-products. The condensation of phenol and formaldehyde to form phenol formaldehyde resins has been discussed already and is shown in Table 1.1. Another example is the condensation of caprolactam with itself to form polycaprolactam (nylon 6) and water, also shown in Table 1.1. The reaction is stepwise or step-growth in the sense that the reaction of each functional group is essentially independent of previous condensation reations. There are no activated species as in addition polymerization.
Revisiting the Early History of Synthetic Polymers: Critiques and New Insights
Published in Ambix, 2018
The other primary type of polymerisation mechanism is known as “step-growth” polymerisation, with the distinction between step-growth polymerisation and chain-growth polymerisation introduced by Paul J. Flory (1910–1985) in 1953.84 Step-growth polymerisation occurs via the repeated coupling of two segments together to result ultimately in a polymeric chain. In the simplest case, this can be viewed as the sequence of two monomers coupling to make a dimer, two dimers coupling to produce a tetramer, two tetramers coupling to make an octamer, etc. The most common example of materials generated via step-growth polymerisation are “condensation” polymers (such as polyesters and polyamides),85 the second general polymer class designation introduced by Carothers in 1929.