The acetal homopolymer is conventionally obtained by the polymerization of formaldehyde, following end capping using acetic anhydride. Asahi Chemical developed a new process to obtain an end-capped polymer during polymerization of highly purified formaldehyde using acetic anhydride as the chain-transfer agent. The use of highly purified formaldehyde and end capping during polymerization using acetic anhydride as a chain-transfer agent or an end-capping agent will provide a simple process for manufacturing the acetal homopolymer. The polymerization mechanism was confirmed by infrared spectroscopy analysis and proton nuclear magnetic resonance (NMR) analysis of the obtained polymer.