Epoxide homopolymerization

The nature of the cure reactions in these epoxies can be confirmed by monitoring the epoxide consumption via near infra-red spectroscopy for a series of epoxide-amine mixtures containing a range of amine contents. A plot of % epoxide consumption vs. amine concentration for DGEBA-T403 epoxies is illustrated in Fig. 2. This plot confirms that the DGEBA-T403 epoxy system forms exclusively from epoxide-amine addition reactions, because (i) 100% epoxide consumption is attained at the stoichiometric amine concentration associated with exclusive epoxide-amine addition cure reactions and (ii) extrapolation of this plot to zero amine content indicates there is no epoxide consumption i.e. there are no epoxide homopolymerization reactions. 

Aluminum-porphyrin complexes, in epoxide homopolymerization, 11, 599 Aluminum(III)-sulfur bonds, mixed covalent and non-covalent systems, 9, 258... 

Aluminum—tetradentate ligand catalyst system, in epoxide homopolymerization, 11, 601 Aluminum(I) tetrahedra, synthesis, 9, 262 Aluminum(III)-tin exchange, process, 9, 265 Aluminum-transition metal bonds, characteristics, 9, 264 Amavadine, for alkane carboxylations, 10, 234—235 Ambruticin S, via ring-closing diene metathesis, 11, 218 Amide-allenes, cyclizations, 10, 718 Amide ether complexes, with Zr(IV) and Hf(IV), 4, 783 Amide hybrid ligands, in organometallic synthesis, 1, 64 Amides... 

Cationic alkyltin species, characteristics, 3, 820 Cationic aluminum catalyst system, in epoxide homopolymerization, 11, 603 Cationic aluminum compounds... 

Anhydride Cured Epoxy Reaction Mechanism. In the case of anhydride cured epoxy reaction, catalysts will promote ring opening of the anhydride to provide carboxylic group for reaction with epoxide. Without catalysts, the reactions are slow and accompanied by extensive epoxide homopolymerization at elevated temperatures. 

The third curing reaction of importance to the aerospace industry is epoxide homopolymerization. The most prevalent is cationic polymerization induced by Lewis acids and may be illustrated as follows ( ... 

Anionic polymerization of epoxides can be induced by Lewis bases (usually tertiary amines) or by metal hydroxides. The amine-type catalysts are by far the most Important type of catalyst for epoxide homopolymerization. The initiation of the polymerization of epoxides has been proposed by Narracott (15) and Newey (16) to result from the attack by the tertiary amine on the epoxide (Reaction 35), with the resulting alkoxlde amine being the propagating species (Reaction 36). 

The methods are at hand to distinguish which mechanism is responsible for the increase in EEW during isothermal aging. The epoxide homopolymerization should have a second order dependence on epoxide concentration and no dependence on secondary alcohol concentration, whereas the epoxide-alcohol reaction should display a first order dependence on both epoxide and secondary alcohol concentration. Therefore, a study of isothermal aging kinetics versus EEW of the epoxy resin will distinguish these mechanisms. 

An homologous series of epoxy resins with various EEWs was synthesized by standard advancement techniques and subsequently esterified with 15 wt% 1300X13. Isothermal aging kinetics were followed at 175C. Aliquots of resin were withdrawn hourly, rapidly cooled to room temperature, and titrated for EEW. No precautions were taken to exclude air during the isothermal aging. Table Xll summarizes the formulations, reactive moiety equivalent weights, and kinetic calculations for the epoxide-alcohol addition reaction and the epoxide homopolymerization reaction. 

Inspection of the formulas of an epoxide and cyclic anhydride side by side reveals that an equimolecular mixture has the elemental composition of a polyester. Only a catalyst is needed to isomerize, in effect, such a mixture to a linear polyester. In such a plymerization, both epoxide and anhydride must be strictly bifunctional toward each other. Careful studies of the uncatalyzed reaction have been made by Fisch and Hoffman [80,81], who showed that some epoxide homopolymerization occurs. This gives systems in which the anhydride is only 0.5 to 0.85 mol per mol of epoxide. 

Note that the activation of the anhydride causes deactivation of the amine. This helps to explain the actual suppression of epoxide homopolymerization by the anhydride-amine combination. 

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