obtained had polydispersities between 1.2 and 1.4 with the end groups for the
majority of polymer chains being initiator/H and only a small quantity of initiator/Br observed. In Sect. 5.2, a few examples demonstrating the advantage of
having functional group on the initiator are discussed.
5.2 Initiation of Polymers from Surfaces
One of the main advantages of external initiation of a polymerization is the ability
to attach different functional groups on the initiator unit that can add an additional
functionality to the polymer chain and interact with the external environment
without disrupting the solid-state packing or the properties of the polymer.
The Kiriy group used the external initiation technique for the synthesis of polymer
brushes by initiating the polymerization of 2-bromo-5-chloromagnesio-3hexylthiophene using the macroinitiator PS-Ni(PPh 3 ) 2 -Br, obtained by oxidative
addition reaction between bromo-substituted polystyrene and Ni(PPh 3 ) 4 . They
immobilized the polystyrene on a glass substrate and initiated the polymerization,
thereby obtaining polymer brushes of 40–70 nm thickness [154, 173]. The brushes
exhibited the properties (solvatochromism and thermochromism) of highly
regioregular P3HT. Kiriy and coworkers further extended this technique by grafting
P3HT chains onto the block copolymer poly(4-vinylpyridine)-b-poly(4-iodostyrene)
[174] and transformed the non-conductive surface of P4VP-b-PS(I) to a
semiconductive surface. A low grafting density of one P3HT unit for every seven
polystyrene units was observed. The grafted films displayed a smooth surface
morphology. The grafted copolymer P4VP-b-PS(I)-graft-P3HT was also grown on
silica particles (micron scale) (Fig. 8). Attempts to detach the grafted copolymer off
the silica particles for the analysis of the P3HT chains were unsuccessful. Senkovsky
et al. also grew P3HT chains on organosilicon nanoparticles [164]. Detachment of
P3HT chains was successful by dissolution of the nanoparticles in HF. Analysis of the
detached P3HT chains showed that the polymers had M n of 43,000 g/mol. The group
managed to grow densely grafted P3HT (with tethering density of 0.28 chains/nm
2
),
which increased the colloidal stability of the nanoparticles.
Sontag et al. explored the growth of polythiophene on gold surfaces by
functionalizing the surface with a 6-(5-bromothiophen-2-yl)hexane-1-thiol
[175]. The more reactive Ni(cod)(PPh 3 ) 2 complex was used for the oxidative
addition with the bromo-end of the thiophene on the functionalized gold surface.
The reactive Grignard species ClMg-Th-I was used for the growth of the polymer
chain. Smooth polythiophene films of thickness ~14 nm could be grown and the
sigma bonding of the films with the surface was confirmed by cyclic voltammetry
(CV) and polarization-mode infrared reflection absorption spectroscopy (IRAS).
The Locklin group further extended the surface initiation technique to indium tin
oxide (ITO) and silica surfaces [148, 178–180]. Phosphonic acid derivatives were
used for interaction with the ITO surface and for the formation of monolayers.
Initiators were formed on these monolayers through the oxidative addition reaction
22
P. Sista and C.K. Luscombe
majority of polymer chains being initiator/H and only a small quantity of initiator/Br observed. In Sect. 5.2, a few examples demonstrating the advantage of
having functional group on the initiator are discussed.
5.2 Initiation of Polymers from Surfaces
One of the main advantages of external initiation of a polymerization is the ability
to attach different functional groups on the initiator unit that can add an additional
functionality to the polymer chain and interact with the external environment
without disrupting the solid-state packing or the properties of the polymer.
The Kiriy group used the external initiation technique for the synthesis of polymer
brushes by initiating the polymerization of 2-bromo-5-chloromagnesio-3hexylthiophene using the macroinitiator PS-Ni(PPh 3 ) 2 -Br, obtained by oxidative
addition reaction between bromo-substituted polystyrene and Ni(PPh 3 ) 4 . They
immobilized the polystyrene on a glass substrate and initiated the polymerization,
thereby obtaining polymer brushes of 40–70 nm thickness [154, 173]. The brushes
exhibited the properties (solvatochromism and thermochromism) of highly
regioregular P3HT. Kiriy and coworkers further extended this technique by grafting
P3HT chains onto the block copolymer poly(4-vinylpyridine)-b-poly(4-iodostyrene)
[174] and transformed the non-conductive surface of P4VP-b-PS(I) to a
semiconductive surface. A low grafting density of one P3HT unit for every seven
polystyrene units was observed. The grafted films displayed a smooth surface
morphology. The grafted copolymer P4VP-b-PS(I)-graft-P3HT was also grown on
silica particles (micron scale) (Fig. 8). Attempts to detach the grafted copolymer off
the silica particles for the analysis of the P3HT chains were unsuccessful. Senkovsky
et al. also grew P3HT chains on organosilicon nanoparticles [164]. Detachment of
P3HT chains was successful by dissolution of the nanoparticles in HF. Analysis of the
detached P3HT chains showed that the polymers had M n of 43,000 g/mol. The group
managed to grow densely grafted P3HT (with tethering density of 0.28 chains/nm
2
),
which increased the colloidal stability of the nanoparticles.
Sontag et al. explored the growth of polythiophene on gold surfaces by
functionalizing the surface with a 6-(5-bromothiophen-2-yl)hexane-1-thiol
[175]. The more reactive Ni(cod)(PPh 3 ) 2 complex was used for the oxidative
addition with the bromo-end of the thiophene on the functionalized gold surface.
The reactive Grignard species ClMg-Th-I was used for the growth of the polymer
chain. Smooth polythiophene films of thickness ~14 nm could be grown and the
sigma bonding of the films with the surface was confirmed by cyclic voltammetry
(CV) and polarization-mode infrared reflection absorption spectroscopy (IRAS).
The Locklin group further extended the surface initiation technique to indium tin
oxide (ITO) and silica surfaces [148, 178–180]. Phosphonic acid derivatives were
used for interaction with the ITO surface and for the formation of monolayers.
Initiators were formed on these monolayers through the oxidative addition reaction
22
P. Sista and C.K. Luscombe