Siloxane oligomers, epoxy-terminated

Piperazine Capping of Epoxy Terminated Siloxane Oligomers... 

An additional way to produce a secondary amine group utilized the reaction of 8 moles of piperazine with 1 mole of the epoxy terminated siloxane oligomer. This reaction was conducted in di-oxane at 60° for about 24 hours. Excess piperazine was removed by washing the oligomer extensively with distilled water. Since the piperazine is water soluble and the oligomer is not, the final system was easily purified to very low levels of residual piperazine in this manner. The product was characterized by titration of the amine endgroups. 

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. 

Poly(unsaturated ester)-siloxane segmented copolymers have been prepared by the polycondensation of epoxy-terminated polydimethylsiloxanes and carboxy-terminated poly(ethylene adipate-co-maleate) oligomers 243). Reactions have been conducted in cellosolve solvent, at 140-150 °C, in the presence of 2% by weight potassium hydroxide catalyst. The molecular weights reported were fairly low. The same group has also prepared poly(hexamethylene adipate)-polydimethylsiloxane copolymers con-... 

Yorkgitis and coworkers [214] have chemically modified epoxy resins with functionally terminated poly (dimethyl siloxane), poly(dimethyl-co-methyltrifluo-ropropyl siloxane), and poly (dimethyl-co-diphenyl siloxane) oligomers and have analyzed the morphology, solid-state properties, and friction and wear properties of the system. They have found that the miscibility of siloxane modifiers in epoxy resins can be enhanced by increasing the percentage of methyltrifluoropropyl siloxane or diphenyl siloxane relative to dimethyl siloxane. 

Most tests were run for 14 kc of disk rotation. However, some materials did not initiate a wear track within the 14 kc, and the tests were extended, in some cases to over 30 kc. Even these extended tests were usually terminated before the wear track initiated. The modifier which produced the longest initiation times was the 20% TFP siloxane co-oligomer when present at 10 and 15 wt.-% in the epoxy. 

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