Abstract: A detailed research on the chloromethylation process was carried out. The chloromethylation of a phenolphthalein polyetherketone resin(PEK-C) was performed in a homogeneous reaction system using 1,4-bis(chloromethoxyl) butane as the chloromethylation reagent and concentrated sulforic acid as the solvent and catalyst. This method is environmentally friendly because of the absence of cancerogenic toxicity of BCMB. Furthermore, this method is more economical because of the low cost of BCMB. The effects of various factors on the chloromethylations were examined. The chemical structure and composition of the chloromethyled phenolphthalein polyetherketone resin(CMPEK-C) were characterized by Fourier transform infrared spectroscopy(FT-IR) and nuclear magnetic resonance(¹H NMR). The experimental results show that the reaction mechanism consists of two kinds of reactions including electrophilic substitution on benzene ring and nucleophilic substitution accompanying by ether linkage fissiond. During the process in preparing CMPEK-C, along with the increase of chlorine content, Friedel-Crafts crosslinking reaction will occur. To prepare the chloromethylated PEK-C with high chlorine content and without obvious cross-linking, the suitable reaction conditions, such as reaction time, temperature influence and the used amount of 1,4-bis(chloromethoxy) butane(BCMB), need to be controlled. The reaction should be carried out at lower temperatures(about 10~30℃) because of the sensitivity of Friedel-Crafts reaction to temperature. Namely, there are two types of effects of reaction conditions on the chloromethylation of PEK-C, one is the influence on PEK-C chloromethylation degree, and the other is the influence on the remaining linearity for PEK-C. The CMPEK-C with 3.4 of chloromethylation degree and complete linearity was obtained under the optimized reaction conditions. The properties of CMPEK-C such as solubility in common organic solvents and thermal stability compared with PEK-C were also studied.