Acetoxyterminated

Acetoxyterminated refers to polymers or oligomers that have acetoxy groups at their chain ends. The acetoxy group is an ester functional group with the structure –O–C(O)–CH3, and end-capping a chain with this group is common in certain silicone materials and related resins. The term is most often encountered in moisture-curing siloxane systems but can apply to other backbones that carry terminal acetoxy groups.

In acetoxy-terminated silicones, the end groups are typically Si–O–C(O)–CH3. Upon exposure to moisture, each acetoxy end hydrolyzes to a silanol (Si–OH) and acetic acid (CH3CO2H). The resulting silanols then condense with other silanols to form siloxane linkages, leading to crosslinking and hardening of the material. This moisture-curing mechanism distinguishes acetoxy-terminated systems from methoxy- or ethoxy-terminated analogues, which release different alcohols during cure.

Applications for acetoxyterminated materials are common in moisture-curing RTV silicone sealants and adhesives used in construction, glazing, and electronics encapsulation. They offer convenient room-temperature cure in humid environments and can provide flexible, durable seals. However, the acetic acid byproduct can impart a vinegar-like odor and, in some cases, cause corrosion or compatibility issues with certain substrates. Proper ventilation and material compatibility considerations are important.

Production involves end-capping hydroxyl- or silanol-terminated polymers with acetyl groups, typically by reacting with acetylating agents such as acetic anhydride or acetyl chloride under appropriate conditions to install the Si–O–C(O)–CH3 termini.