Synthesis and characterization of a novel hydroxyl-terminated polydimethylsiloxane for application in the silicone-modified acrylic-grafted polyester resins

Monoallyl-end-capped polypropylene glycol (MPG) was successfully synthesized by the reaction of polypropylene glycol and allyl chloride. Also, hydrogen-terminated polydimethylsiloxane (H-PDMS) was prepared by the reaction of dichlorodimethylsilane and chlorodimethylsilane (CDMS). Then, MPG and H-PDMS were reacted to produce hydroxyl-terminated polydimethylsiloxane (OH-PDMS) as silicone which is used to prepare automotive pre-painted or coil-coated metals (PCM). This pre-coated metal PCM system was investigated to remove the wet-coating process, such as pre-treatment and spray coating for environmental regulations. However, automotive pre-coated metal must have high flexibility and stiffness to overcome the harsh conditions such as those encountered in the cutting, pressing, and stamping process. For these reasons, a series of silicone-modified acrylic-grafted polyester (SAGP) resins (e.g. SAGP-0–SAGP-10) were designed to satisfy both the hardness and the flexibility for an automotive PCM. The OH-PDMS (silicone) was characterized by Fourier transform-infrared (FT-IR), ¹H-NMR, and ¹³C-NMR spectroscopic techniques. The results showed that the targeted product was successfully carried out. The structural elucidation of the synthesized SAGP was carried out by FT-IR spectroscopic technique. Thermal properties of the resins were studied using thermogravimetric analysis and differential scanning calorimetry. The flexibility of the resins was measured by tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement.