Charge the first two materials to a 1-l flask fitted with a thermometer, stirrer and inert gas inlet. Adjust the inert gas flow to 0.1 l per min and heat the batch to 260'C (500'F). Hold at temperature for an acid number of 1-2. Cool the contents of the flask to 200'C and add the phthalic anhydride. Reheat to 240'C and hold for an acid number of 3-5 and a viscosity of V-X at 50% N.V. in xylene. Cool and reduce with xylene.
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