Epoxy resins termination step

After these preliminary studies, McGrath and co-workers have used ethylpiperazine terminated siloxane oligomers with varying molecular weights and backbone compositions throughout their studies 69 114,11S). Modifications of epoxy resins with siloxane oligomers were performed in two steps as depicted in Reaction Scheme XXIII. 

Siloxane-modified networks were prepared for testing via two steps. A linear precursor was generated by reacting the epoxy resin with the siloxane oligomer for one hour under vacuum at 65 °C. PACM-20 was then added, and the mixture was stirred for five minutes under vacuum at 50 °C. Previous studies indicated 151 that reaction between the AEP-terminated siloxane oligomers and the curing agent is not possible, as one would expect. 

A typical cationic uv adhesive formulation contains an epoxy resin, a cure-accelerating resin, a diluent (which may or may not be reactive), and a photoinitiator. The initiation step results in the formation of a positively charged center through which an addition polymerization reaction occurs. There is no inherent termination, which may allow a significant postcure. Once the reaction is started, it continues until all the epoxy chemistry is consumed and complete cure of the resin has been achieved. Thus, these systems have been termed living polymers. 

Epoxy resins are complex network polyethers usually formed in a two-staged process. The first stage involves a base-catalyzed step-growth reaction of an excess epoxide, typically epichlorohydrin with a dihydroxy compound such as bisphenol A This results in the formation of a low-molecular-weight prepolymer terminated on either side by an epoxide group. 

Figure 3.2 (a) Epoxy resin synthesis generalized reaction (b) reaction of hydroxyl group of NaOH with proton (c) displacement of the chlorine atom by the hydroxyl group (d) chain propagation (e) termination step. 

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. 

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