polyester resins 1-8-08

polyester resins 1-8-08 - Polyester and Vinyl Ester Resins...

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1 Polyester and Vinyl Ester Resins Douglas J. Gardner Professor Wood-Polymer Hybrid Composites Polymer Reactions
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2 Chain (or Addition) Polymerization • Chain polymerization is characterized by the presence of a few active sites which react and propagate through a sea of monomers. Polymerization may occur by any of three mechanisms: – free radical – cationic – anionic Crosslinking In Chain Polymerizations • It may be formed via a two step process, where a polymer with unsaturations is first formed (a thermoplastic formed via step polymerization), and then these unsaturated sites are reacted with a crosslinking agent in a second step to produce the final structure
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3 Step Polymerization In a step reaction mechanism, monomers can react with any nearby monomer. In contrast to chain polymerization, no special activation is needed to allow a monomer to react. Frequently these reactions are copolymerizations, where two types of monomer are present and each reacts only with the other (and not with monomers like itself) This type of polymerization is also called condensation polymerization because water is often liberated when the polymer bonds form. Crosslinking In Step Polymerization • In step polymerization, functionality is defined as the number of reactive ends or parts. The effects of average functionality (f) are: – f less than 2: low molecular weight – f equal to 2: linear polymer – f greater than 2: branched or crosslinked polymer
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4 The Time-Temperature- Transformation diagram Gelation The incipient formation of an infinite molecular network. Vitrification The glass transition temperature of the forming polymer rises above the temperature of cure. Full cure highest attainable degree of cure Devitrification This is degradation. Polyesters • Polyesters are subdivided into three classes – Aliphatic –A rom a
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5 Polyester Resin Formation Polyester resins are manufactured by a step polymerization reaction of glycols with unsaturated or saturated acids or anhydrides. Glycols
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This note was uploaded on 12/21/2010 for the course AEWC 430 taught by Professor Dg during the Fall '08 term at University of Maine Orono .

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polyester resins 1-8-08 - Polyester and Vinyl Ester Resins...

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