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.
ASJC Scopus subject areas
- Materials Chemistry