Effect of Metal Alkoxide Complexes on Condensation Reactions of Hydrolyzed Phenyltriethoxysilane

Metal alkoxide complexes, in which alkoxy groups were substituted with ethyl acetoacetate (EAcAc), were found to accelerate condensation reactions of hydrolyzed phenyltriethoxysilane (PTES) and affect the structure of phenylsiloxane networks. The ²⁹Si NMR study revealed that the acceleration effect increased in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc)_x < Ti(OC₂H₅)_4–x (EAcAc) _x . However, the GPC study revealed that the solution contained the high molecular weight species in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc) _x . In the case of Ti(OC₂H₅)_4–x (EAcAc) _x , the smaller size of phenylsiloxane networks with a low content of silanol groups was formed in the solution. In the case of Ta(OC₂H₅)_5–x (EAcAc) _x , the larger size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. In the case of Al(O-sec-C₄H₉)_3–x (EAcAc) _x , the small size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. During gelation, the catalytic effect of the metal alkoxide complexes on the development of phenylsiloxane networks was also found. However, the average molecular weight of the gels increased in the order Ta(OC₂H₅)_5–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x Al(O-sec-C₄H₉)_3–x (EAcAc) _x . The metal alkoxide complexes were hydrolyzed and finally incorporated into the phenylsiloxane networks of gels to form M—O—Si bonds, which were indicated by the results of FT-IR analysis.