In the plastics, rubber, and coatings industries, large amounts of inorganic fillers (such as silica, aluminum hydroxide, and talc) are often added to reduce costs or improve performance. However, untreated fillers are prone to agglomeration and are difficult to disperse, which weakens the mechanical properties of the material. 3-Chloropropyltrimethoxysilane (CPTMS) provides an efficient solution to this problem.

By surface-modifying fillers with CPTMS, its methoxy groups react with the hydroxyl groups on the filler surface to form covalent bonds, while the chloropropyl chains extend outward, giving the filler surface organic compatibility. This not only significantly improves the uniformity of filler dispersion in the resin matrix but also enhances interfacial bonding. For example, in flame-retardant cable materials, aluminum hydroxide fillers treated with CPTMS not only distribute more uniformly but also form a denser char layer during combustion, improving flame-retardant efficiency; simultaneously, the tensile strength and elongation at break of the material are significantly better than those of the untreated system.

Furthermore, CPTMS can also serve as a functionalization intermediate—its chlorine atoms can further react with polyamines to generate aminosilanes, which can be used to prepare more active coupling agents. This flexibility of "one-step modification and multiple-step expansion" makes it highly favored in the development of high-end composite materials.