engleski

Impact of amine structure on the outcome of γ- irradiation of PDMS-based gel networks

PDMS-based "gel networks" [1] with gel-like properties but without a liquid component were obtained by low temperature curing of diglycidyl ether terminated poly(dimethylsiloxane), PDMS-DGE with selected aliphatic amines. Three diamines 1, 3-diamino- 2- propanol (DAP), diethylenetriamine (DETA) and triethylenetetramine (TETA) and a triamine tris(2-aminoethyl)amine (TAEA) were reacted with PDMS-DGE at 50 oC. To assess their stability to ionizing radiation, obtained gel networks were irradiated in ambient conditions at 60Co γ-irradiation facility of LRCD, RBI. Gamma irradiation of PDMS can induce both crosslinking and degradation by chain scission. [2] Because non-irradiated gel networks contained unreacted epoxy groups [3] it was expected that radiation crosslinking will prevail over degradation. While the apparent firmness of gel networks irradiated up to 50 kGy was preserved, Soxhlet extraction in hexane revealed only a slight increase in gel content of most gel networks and even a slight decrease in case of TAEA cured gel network. The changes in thermal and dielectric properties were more pronounced and the radiation response was clearly influenced by the structure of used amine. The gel networks prepared using the amines that can either form hydrogen bonds like DAP or produce denser network like TAEA because of three primary amine groups were less influenced by irradiation. The conductivity of non-irradiated DAP cured gel network was the lowest and it increased very little on irradiation. On the other hand both electrical conductivity and the enthalpy of endothermic transition of DETA cured gel network increased significantly on irradiation and its conductivity was almost 2 orders of magnitude greater than that of corresponding non- irradiated one. In case of irradiated TETA cured gel network a slight reduction of the enthalpy of endothermic transition was observed and conductivity change was lower than for DETA cured one. Since Soxhlet extraction of irradiated TETA cured gel network showed a 10% higher gel content all this indicates that its initial curing was less complete than in case of DETA although the diamines have very similar structure. Even though contribution of DAP, DETA, TETA and TAEA segments to cured PDMS gel networks is relatively small their structure significantly influenced not only the properties on initial curing but also the outcome of irradiation even at a relatively low dose of 50 kGy.

PDMS ; aliphatic amines ; gamma-irradiation

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