Silane coupling agents structure

The adhesion promotion of an organic matrix to an inorganic substrate using a silane has been studied to model the structure of the created interphase [64-66]. The polymer/silane interphase is influenced by the solubility parameter of both the silane coupling agent and the polymer. More interdiffusion occurs when the solubility parameters of the polymer and the silane closely match together. It is believed that this model can be applied to silicone adhesive/solid substrate system. 

Various additives and fillers may be employed. Calcium carbonate, talc, carbon black, titanium dioxide, and wollastonite are commonly used as fillers. Plasticizers are often utilized also. Plasticizers may reduce viscosity and may help adhesion to certain substrates. Thixotropes such as fumed silica, structured clays, precipitated silica, PVC powder, etc. can be added. Adhesion promoters, such as silane coupling agents, may also be used in the formulation [69]. 

Table 5a Structures and Physical Properties of Silane Coupling Agents...

The structure of the silane coupling agent is expressed by the general formula -l-(RO)3—Si—R, where the RO... 

Figure 13.1 The general structure of a silane coupling agent includes a functional group or reactive group at the end of an organic spacer This alkyl chain is attached to the central silicon atom, which also has up to three hydrolysable groups attached to it.

Another highly effect chain extender is trimellitic anhydride (TMA) which gives rise to branching of the PET structure. Note that the multifunctional epoxies (see Table 14.2) react quickly with the terminal carboxylic acid groups of PET but can also react with the film former and the silane coupling agent on glass fibre reinforcements. 

Ishida, H., Chiang, C.H. and Koenig, J.L. (1982). The structure of aminofunctional silane coupling agents. Polymer 23, 251-262. 

Fig. 14. Effect of the chemical structure of silane coupling agents on their adsorption on the surface of a CaC03 filler, r=1.25pm (O) aminosilane (AMPTES), (A) aliphatic silane (SPIES)... 

Han [17] has shown that the effect of silane coupling agents on the viscosity of filled thermoplastics is not consistent. Melt viscosity may be decreased or increased depending on the chemical structure of the treatment and the nature of the polymer/filler combination under consideration. These observations probably reflect the effectiveness of the coupling agent in promoting bonding between filler and polymer, and hence the extent of polymer immobilization. 

Abstract—When K. L. Mittal asked me to provide a historical account of the applications of silane coupling agents in adhesion. I decided to write in the form of a personal account of my last 45 years in this line of study. No attempt is made to make the history comprehensive, or to recognize the host of other researchers who have contributed to our understanding of adhesion across an interface of dissimilar materials. It has been an immensely interesting area of study with many practical applications in composites and bonded structures. 

Several modifications of commercial silane coupling agents have been evaluated to search for improved bonding at the interface. These approaches attempt to use modifiers to counteract basic faults of the individual silanes. Some of these modifications include increased hydrophobic character, increased crosslinking of the siloxane structure, increased thermal stability, and ionomer bond formation to reduce shear degradation at the interface. 

Silane coupling agents have the structure R—Si—X3, where R represents an organofunctional group and X is generally alkoxy. They are generally applied from water solutions or from organic solvent-water mixtures. In the presence of water, hydrolysis occurs step-wise to form alkoxysilanols, and eventually silane triols. Condensation of the silanols to siloxanes also occurs. Reactions shown schematically below ... 

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