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Polymer-based nanocomposites 161

Monomer
Initiator

“Grafting from” “Grafting through” “Grafting onto”
Fig. 5.8 Schematic illustration of the attachment of polymers to surfaces.
Reprinted with permission from Bousqueta A, Awadaa H, Hiornsb RC, Dagron-Lartigaua C,
Billon L. Conjugated-polymer grafting on inorganic and organic substrates: a new trend in
organic electronic materials. Prog Polym Sci 2014;39:1847–77. Copyright 2014 Elsevier Ltd.

diffusion of small organic compounds to the growing chain-ends, namely, monomer
molecules [264]. One more method called “grafting through” (Fig. 5.8) is based on the
anchoring of a polymerizable group [265]. During the propagation step after polymer
chain initiation, the growing chains interact with the functional groups attached on the
surface and then further propagate with free monomers. However, the surface density
and length of the polymer chains grafted are very difficult to control in this technique.

5.5 Role of anchoring groups

Determining the nature of the anchoring group attaching the polymer to the substrate
helps us understand a well-defined polymer monolayer. The ordered molecular assem-
blies exhibited by the adsorption of an active molecule resulted in self-assembled
monolayers (SAMs). Using the anchoring method makes SAMs inherently easy to
approach to industrial processes for, it is technologically attractive for surface engi-
neering and fabricating superlattices. The order in these two-dimensional SAM sys-
tems is maintained by a spontaneous chemical synthesis at the interface, as the system
approaches equilibrium. Depending on the nature of the substrate, various chemical
moieties can be exploited, namely, diazonium [266,267], sulfur [268], silicon [269],
and phosphorous-based anchoring functional groups (Fig. 5.9) [270].
These functional groups have been largely explored for surface-initiated polymer-
ization or “grafting onto” techniques in combination with controlled radical polymer-
ization techniques [271]. Nevertheless, now, they have been employed in organic
electronics to attach conjugated polymers to inert or electroactive surfaces. Various
approaches were used to attach polymers to a surface through an anchoring group
where the polymer carries the anchoring group, either as a side chain or an end group.
The end-chain approach causes surface-attached monolayers where the chains are ori-
ented perpendicularly to the surface. Contrarily, side-chain attachment usually
exhibits multiple anchorages and thus a flat conformation of chains [272].