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Synthesis, properties and applications of epoxy resins and polyurethanes.

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Epoxy resins
Synthesis: Epoxy resins or plastics are typically formed by the reaction of epichlorohydrin and
bisphenol A:
The reaction actually involves the sodium salt of bisphenol A since polymerization is carried
out in the presence of an equivalent of sodium hydroxide. Reaction temperatures are in the range 50–
95 C. Side reactions (hydrolysis of epichlorohydrin, reaction of epichlorohydrin with hydroxyl groups
of polymer or impurities) as well as the stoichiometric ratio need to be controlled to produce a
prepolymer with two epoxide end groups. Either liquid or solid prepolymers are produced by control
of molecular weight; typical values of n are less than 1 for liquid prepolymers and in the range 2-30
for solid prepolymers.
A variety of coreactants are used to cure epoxy resins, either through the epoxide or hydroxyl
groups. Polyamines are the most common curing agent with reaction involving ring-opening addition
of amine:
Both primary and secondary amines are used; primary amines are more reactive than
secondary amines. Since each nitrogen-hydrogen bond is reactive in the curing reaction, primary and
secondary amine groups are biand monofunctional, respectively. A variety of amines are used as
crosslinking agents, including diethylene triamine, triethylene tetramine, 4,4-diamino-
diphenylmethane, and polyaminoamides (e.g., the diamide formed from diethylene triamine and a
dimerized or trimerized fatty acid). Other types of compounds have also been used to cure epoxy
resins via the epoxide groups, including polythiols, dicyandiamide (cyanoguanidine), diisocyanates,
Synthesis, properties and applications of epoxy resins and polyurethanes.

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Synthesis, properties and applications of epoxy resins and polyurethanes.Epoxy resinsSynthesis: Epoxy resins or plastics are typically formed by the reaction of epichlorohydrin andbisphenol A:The reaction actually involves the sodium salt of bisphenol A since polymerization is carriedout in the presence of an equivalent of sodium hydroxide. Reaction temperatures are in the range 5095 C. Side reactions (hydrolysis of epichlorohydrin, reaction of epichlorohydrin with hydroxyl groupsof polymer or impurities) as well as the stoichiometric ratio need to be controlled to produce aprepolymer with two epoxide end groups. Either liquid or solid prepolymers are produced by controlof molecular weight; typical values of n are less than 1 for liquid prepolymers and in the range 2-30for solid prepolymers.A variety of coreactants are used to cure epoxy resins, either through the epoxide ...
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