Poly(2,6-dimethyl-1,4-phenylene oxide) with exactly one functional endgroup was synthesized by oxidative polymerization, halogen substitution polymerization, and by phase transfer catalysis. Reaction with 4-vinylbenzoyl chloride resulted in a quantitative conversion to a macromonomer as shown by GPC and endgroup analysis. The macromonomer is a glassy material with a Tg from 150 to 190°C depending on the molecular weight.