Step-growth polymers epoxy resins

Step-growth, or condensation, polymers are usually formed in a reaction between two monomers, each of which is at least difunctional. Polyesters, polyamides, polyurethanes, and epoxy resins are typical examples of step-growth polymers. These polymers grow by steps or leaps rather than one monomer unit at a time. 

Epoxy resins represent a class of step-growth polymer familiar to anyone who has used epoxy to glue together a broken object. An epoxy resin consists of two components a fluid prepolymer composed of short polymer chains with reactive epoxides on each end, and a hardener, usually a diamine or triamine that ring opens the epoxides and cross-links the chains together. 

Epoxy resin (Section 30.6E) A step-growth polymer formed from a fluid prepolymer and a hardener that cross-links polymer chains together. 

Write a mechanism for a step-growth polymerization, as in the formation of a polyester, polyamide, polyurethane, epoxy resin of phenol-formaldehyde polymer. 

Epoxy resins are a class of polymers that can be crossllnked to yield materials with a wide range of physical and chemical properties. Usually, linear, low-molecular weight products, known as pre-poljnners or first-stage polymers are polyethers with reactive epoxide endgroups. The most commonly used prepolymer is prepared by the condensation or step-growth polymerization of epichlorohydrin and bisphenol A as shown by the following equation ... 

Many thermoset polymers of major commercial importance are synthesized by step-growth polymerization, as the case of unsaturated polyester, polyurethanes, melamines, phenolic and urea formaldehyde resins, epoxy resins, silicons, etc. In these systems, the crosslinking process, which leads to a polymer network formation, is usually referred to as curing. 

Polyaddition and polycondensation reactions usually lead to functional polymers, since the polymers produced are terminated with reactive functional groups. A higher degree of functionality is easily affordable if monomers with additional reactive groups are used that do not participate in the step-growth polymerization. In emulsion polymerizations, neither polyaddition nor polycondensation reactions can be carried out consequently, the miniemulsion technique is of special interest as no diffusion of the monomers takes place. The first polyaddition in miniemulsion were performed in 2000, with the reaction of polyepoxides and hydrophobic diamines, bisphenols, and dimercaptanes [105]. Stable latexes of epoxy resins could be obtained, and apparent molecular weights of up to 20 000 g mol were measured. 

Important commercial polymers synthesized through step-growth processes include polyamides, polyesters, polycarbonates, polyurethanes, and epoxy resins. 

Anionic and Cationic Polymerizations o Radical Polymerization Advances o Coordination Polymerizations 0 Step-Growth Polymerization Advances 0 Synthesis of Tactic Polymers o Stereoblock Copolymers o Dispersion Polymerizations o Cellulosic Graft Copolymers o Diels-Alder Polymer Forming Reactions o A New Path To Phenolic Resins o Nitrogen Heterocycle Polymerizations o Optically Active Polymers o Poly (Phenylene Sulfide) o Poly (Aryl Ethers) o (Poly (Aryl Ether Sulfones) o Epoxy and Isocyanate Resin Replacement o Azlactone Functionalized Oligomers o Epoxy Resin-Isocyanate Reactions o Chelating Polymers o Oxazoline Functionalized Polymers o Poly (Alkyl Methacrylates) o Macromers... 

Epoxy adhesives represent the most common structural adhesives and have gained wide acceptance in many diverse industries. They essentially consist of an epoxy resin, often based upon the diglycidyl ether of bisphenol A, and harden to give a thermosetting polymer by step-growth polymerization or addition polymerization. 

Typical epoxy resins used to formulate epoxy adhesives have at least two epoxy rings, usually at the ends of a relatively short-chain prepolymer. The epoxy groups then are reacted with other epoxy groups in a chain-growth polymerization or with another curative in a step-growth polymerization to produce a polymer network, which can be either thermoplastic or thermoset, The polymer linkages created by reaction of the epoxy ring are polar... 

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