Yoshiyuki Sugahara, Tsuyoshi Inoue and Kazuyuki Kuroda
Hydrolysis and initial polycondensation processes in the Si(OEt)4 (TEOS)–RSi(OEt)3 –EtOH–water–HCl systems (R=Me, Ph) [TEOS:RSi(OEt)3:EtOH:water:HCl=1:1:24:x:y (x=12, 2/3; y=2×10-3 , 4×10-3 , 8×10-2 )] have been investigated by using 29Si NMR spectroscopy. For comparison, the alkoxysilanes [TEOS, MeSi(OEt)3 (MTES), PhSi(OEt)3 (PTES)] were hydrolysed separately in a similar manner. In a water-rich TEOS–MTES system (water:Si=12:1), a silanol-terminated codimer [Me(HO)2SiOSi(OH)3 ] was detected as well as (HO)3SiOSi(OH)3 and Me(HO)2SiOSi(OH)2Me, suggesting that the hydrolysed monomers were condensed rather randomly. In contrast, in a water-rich TEOS–PTES system, hydrolysed monomers derived from TEOS and those from PTES were condensed independently; a silanol-terminated codimer [Ph(HO)2SiOSi(OH)3 ] did not form, and only (HO)3SiOSi(OH)3 and Ph(HO)2SiOSi(OH)2Ph were detected. These observations in the TEOS–PTES system suggest the presence of the association of the phenyl groups. In water-restricted systems (water:Si=1:3), monomers were only partially hydrolysed, and ethoxy-terminated codimers [R(EtO)2SiOSi(OEt)3 (R=Me, Ph)] formed in both the TEOS–MTES and the TEOS–PTES systems.