Trifunctional modifiers

Figure 2.26. Reformation of additional silanol groups during processing when trifunctional modifiers are used.

All monofunctional modifiers decrease the surface concentration of silanols by 50% (depending on the alkyl ligand) compared to original silica (7.6pmol/m ), while difunctional modifiers only slightly reduces the surface concentration of silanols by 12% and trifunctional modifiers apparently increases the amount of silanols. This reflects actual hydrolysis of nonreacted chlorine groups of the alkyl di- and trifunctional modifiers and their conversion into silanols. 

When a trifunctional modifier is used each surface silanole is substituted with two hydroxyls, as shown in the following reaction ... 

Weber, W. P. Paulasaari, J. Cai, G. Synthesis of Linear Copolysiloxanes with Regular Microstructures and Synthesis of Soluble Polysiloxanes with Trifunctional RSi03/2 (T) or Tetrafunctional Si04/2 (Q) Units. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 72-78. 

Macromonomers carrying mono-, bi- or trifunctional end groups are sometimes important constituents of a network. Through them, terminating, chain-extending, or crosslinking units are introduced to modify the network... 

Structure II polymers are relatively elastic when polymethylphenylsiloxanes are obtained by the hydrolytic cocondensation only of trifunctional monomers (e.g., methyl- and phenyltrichlorosilanes), there are polymers with low elasticity. Polydimethyl- and polymethylphenylsiloxanes can be modified with organic polymers (polyester, epoxy) or silicone substances, e.g. methyl(phenylaminomethyl)diethoxysilane. The modification of polydimethyl- and polymethylphenylsiloxanes improves some properties of these polymers and varnishes based on them in particular, it considerably increases adhesion and mechanical durability of varnish films. 

For reverse-phase chromatography purposes, silica sorbents are commonly modified by hydrophobic ligands by means of silanes. These systems are therefore particularly suitable for water intrusion experiments [7]. We studied the influence of the chain nature (perfluorated, alkyl), the chain length and the type of bonding chemistry (mono or trifunctional, chloro- or alkoxy- silanes) on the hydrophobic properties of silica gels. 

Depending on the surface modification reversed phase silicas can be grouped into (a) monomeric reversed phase silicas chemically modified with monofunctional silanes and (b) polymeric reversed phase silicas with a polymeric layer made by surface reaction with trifunctional silanes. 

---