Inorganic reinforcing materials such as glass fiber, quartz powder, and mica play a "skeleton" role in composite materials, but their surface inertness often leads to poor bonding with the resin matrix. 3-Chloropropyltrimethoxysilane (CPTMS), as a reactive surface treatment agent, is gradually becoming an effective supplement to traditional silanes (such as KH-550).

In glass fiber sizing agent formulations, CPTMS can work synergistically with other film-forming agents. Its hydrolyzed siloxane portion is firmly adsorbed onto the glass fiber surface, while the chloropropyl group provides potential for subsequent reactions. Although the chlorine atom itself has low reactivity, during high-temperature curing, it can substitute with amine accelerators in the resin to form C–N bonds, achieving "delayed crosslinking" and helping to improve the interfacial shear strength of the final product.

In the treatment of mineral fillers (such as wollastonite and glass microspheres), the organic coating layer formed by CPTMS not only improves flowability but also reduces the interference of the filler on the resin curing system. It is particularly suitable for color-sensitive applications or applications where yellowing must be avoided (such as light-colored paints) because CPTMS does not contain easily oxidized amino groups and has superior thermal stability.