Trimethoxysilane Coupling Agents: Hydrolysis Kinetics by FTNIR PLS Model, Synthesis and Characterization of Fluorinated Silicone Resin

To explore the hydrolysis rules of the methoxysilane coupling agents (MSCA), the Fourier transform near infrared (FTNIR) spectroscopy combined with the partial least squares (PLS) model were successfully applied to study the hydrolysis kinetics of the phenyltrimethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, (3, 3, 3-trifluoropropyl)trimethoxysilane and (1H, 1H, 2H, 2H-perfluorooctyl)trimethoxysilane in a HCl-catalyzed EtOH system. The fluorinated silicone resin was synthesized by the hydrolysis and copolycondensation reactions of the 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane and methyltrimethoxysilane. The results were listed as follows: (1) the fast scanning speed, no sampling characters of the FTNIR spectroscopy, and the data processing ability of the PLS, enabled the method to “catch” the fast changing [H 2 O] accurately in real time with the resolution of 23 s. (2) The hydrolysis reactions were second-order reactions, the measured results were in good agreement with the theoretical kinetic equations in the primeval stage. Both temperature and acidity could promote the hydrolysis reactions. The applicable pH of this method was 3 ~ 7. The rate constant of the PTMS was sensitive to the temperature. The phenyl was unfavorable while the vinyl was favorable to the hydrolysis reaction. (3) The fluorinated silicone resins could hardly be cured without catalysis when the n(PFOTMS)/(n(MTMS) + n(PFOTMS)) was higher than 75%. The steric hindrance of the bulky long-chain 1H, 1H, 2H, 2H-perfluorooctyl had nearly no affect on the hydrolysis reactions in the dilute solutions, but strongly hindered the curing processes in the sticky systems. The introduction of the F atoms brought a great rise of hydrophobicity and thermostability to the silicon resin.