Step-growth polymerizations epoxy resins

Step-growth polymerization. Epoxy resins were prepared from nadlc methyl anhydride and Epon 828. This blfunctlonal oxirane also supplies reactive hydrogen sites. The major component is at 1=0, minor components include oligomers with 1=1,2,3. Their concentrations rapidly diminish as degree of polymerization Increases. 

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. 

Esterification need not be the reaction concerned polyamides, epoxy resins, amino resins and others are produced by step growth polymerization. It is worth mentioning that, in these polymerizations, the by-product is almost always unwanted and must be removed before the resin can be used. Water, for example, is immiscible with polyester resins and can be removed by distillation during the polymerization. Removal of the by-product accelerates the polymerization, and is essential to moving the reaction along. 

Step-growth polymerization of a diepoxide and a diamine gives an epoxy resin (Section 16.4E)... 

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... 

Step-Growth Polymerization of a Diepoxide and a Diamine Gives an Epoxy Resin (Section 29.5E)... 

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... 

During isothermal polymerization below Tg, the molecular weight and T, increase, and eventually T, will equal Tjure The main purpose of this section is to discuss the calculation of the time to vitrification, where vitrification is defined to occur when Tj, equals T ure- The concepts of vitrification and the TTT cure diagram are extended to linear systems for both step growth and chain reaction mechanisms, although most of the discussion will focus on the nonlinear step growth case, of which the cure of epoxy resins is an example. 

The formation of networks by addition polymerization of multifunctional monomers as minor components included with the monofunctional vinyl or acrylic monomer is industrially important in applications as diverse as dental composites and UV-cured metal coatings. The chemorheology of these systems is therefore of industrial importance and the differences between these and the step-growth networks such as amine-cured epoxy resins (Section 1.2.2) need to be understood. One of the major differences recognized has been that addition polymerization results in the formation of microgel at very low extents of conversion (<10%) compared with stepwise polymerization of epoxy resins, for which the gel point occurs at a high extent of conversion (e.g. 60%) that is consistent with the... 

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