NCO Analysis: Continued

• Titrate with 1.0 N hydrochloric acid to a yellow end point, using 0.5 mL of bromophenol blue indicator.
• Run a blank
• Calculate %NCO
  • %NCO=(mL HCl blank-mL HCl sample)/sample wt

• Prepolymer should contain %NCO = 7.75

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