Effect of Metal Alkoxide Complexes on Condensation Reactions of Hydrolyzed Phenyltriethoxysilane

Abstract

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.