I have synthesized a polyurethane elastomer inspired to the composition of Estane 58888TM (pTHF 1000g/mol, MDI, BDO - 46% HS). I synthesized my PU via two-step method with 51% HS content, and then, by solution casting, I obtained films of about 100 um.
The discrepancy is the fact that while films made with EstaneTM have electrical resistance of 1012 Ohm, my films have resistances that range between 106-108 Ohm.
Since I want the resistance as high as possible, can someone suggest me what are the possible causes of this behaviour?
Are you sure that other properties of your synthesized samples is similar to the Estane? At first, you can compare physical properties of your samples with the commercial sample, then contact with me. If there is difference ,your synthesis process may be is one of obstacles.
I propose reduction in HS content as 30-35 % at first and evaluate any increasing or deceasing in resistance of your PUs. Then according to the obtained results I will help you. Good luck.
Dear Mrs. Gity,
thank you for the reply and the suggestion. I will inform you on the measurement result of the material with the reduced HS content.
Thinking about the synthesis process, is possible that reaction time of the steps affect the electrical properties of the final product? I pre-polymerize 4h or more, and chain extend for 1-2 minutes, both under mechanical stirring and nitrogen blanket. Is the chain extensions time too short?
Best regards.
Fabio
There maybe two reasons: the first is that the stoichiometry is not exactly 100 so that you have some free OH groups decreasing the resistance by several orders of magnitude (this maybe result from incorrect determination of OH and NCO values and water content not incorporated in the calculation). The second reason may trace impurities such as heavy metals in your raw materials; this you have to rule out by trace analysis and, in case there are, by ion chromatography.
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