30
3.2.3.3.3 Reversible Addition-Fragmentation Chain Transfer
Polymerization (RAFT)
This method relies on the use of chain transfer agents (e.g. dithioesters, dithiocarbamates, etc.), which react with the propagating chain-end to form adducts, which
return to the original reactants or fragment to produce a free radical, and thus maintain the equilibrium between the active and dormant states of the propagating radicals. The advantage of this method is its wide applicability, since conventional free
radical polymerization can be turned into a controlled process with the addition of
a suitable chain transfer agent.
Poly(methacrylic acid) was grafted by Söylemez et al. (2018) onto polyethylene/
polypropylene fabrics under gamma radiation, using cumyl dibenzoate as the RAFT
agent. Lan et al. (2017) also used a similar method to graft poly(glycidyl methacrylate) using 4-cyano-4-[(phenylcarbonothioyl)thio]pentanoic acid as RAFT agent,
while poly(glycidyl methacrylate) was grafted onto carbon fibers using
2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as the RAFT agent
from the monomers dissolved in dimethyl formamide after pretreating the fibers to
affix the RAFT agent onto fibers with a silane. In line with this, Xiong et al. (2017)
grafted poly(acrylamide) onto carbon fibers using 2-(ethoxycarbonyl)prop-2-yl
dithiobenzoate as a RAFT agent, after a pretreatment to affix the RAFT agent onto
the fibers with a silane.
Silk fibers modified with the coupling agent 3-(trimethoxysilyl) propyl methacrylate were grafted by Buga et al. (2015) from methyl methacrylate and tributylsilyl
methacrylate using 2-cyanoprop-2-yl dithiobenzoate as a RAFT agent. Yang et al.
(2013) grafted silk fibers with N,N-dimethylacrylamide using macromolecular
RAFT agents synthesized from acrylic acid, styrene, n-butyl acrylate and 2-(((dodecylsulfanyl) carbonothioyl) sulfanyl) propanoicacid to allow tuning of the radical
reactivity by control of the macromolecular composition.
The literature also reports that ramie fibers have been first modified with
2- bromisobutyryl bromide and carbon disulfide to produce 2-dithiobenzoyl isobutyrate moieties and then grafted with methyl acrylate, methyl methacrylate, styrene
and p-chlorostyrene using 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as a RAFT
agent (Chen et al. 2009; Yi et al. 2010). A similar procedure for grafting from
trifluoroethyl methacrylate onto ramie fibers in supercritical carbon dioxide was
carried out by Liu et al. (2010).
3.2.4 Polymer Deposition
Polymer deposition is another method for surface modifications of fibrous polymers
with other polymers, and also includes ‘grafting-to’ approaches. Günay et al.
(2017b, b) found that a conjugation with cyclic polypeptides increases the deposition of polymeric treatment agents based on poly(hydroxypropyl methacrylamide),
poly(styrene-co-acrylic acid) and polyurethane, onto cellulose fibers and proteins,
A. P. Manian et al.
3.2.3.3.3 Reversible Addition-Fragmentation Chain Transfer
Polymerization (RAFT)
This method relies on the use of chain transfer agents (e.g. dithioesters, dithiocarbamates, etc.), which react with the propagating chain-end to form adducts, which
return to the original reactants or fragment to produce a free radical, and thus maintain the equilibrium between the active and dormant states of the propagating radicals. The advantage of this method is its wide applicability, since conventional free
radical polymerization can be turned into a controlled process with the addition of
a suitable chain transfer agent.
Poly(methacrylic acid) was grafted by Söylemez et al. (2018) onto polyethylene/
polypropylene fabrics under gamma radiation, using cumyl dibenzoate as the RAFT
agent. Lan et al. (2017) also used a similar method to graft poly(glycidyl methacrylate) using 4-cyano-4-[(phenylcarbonothioyl)thio]pentanoic acid as RAFT agent,
while poly(glycidyl methacrylate) was grafted onto carbon fibers using
2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as the RAFT agent
from the monomers dissolved in dimethyl formamide after pretreating the fibers to
affix the RAFT agent onto fibers with a silane. In line with this, Xiong et al. (2017)
grafted poly(acrylamide) onto carbon fibers using 2-(ethoxycarbonyl)prop-2-yl
dithiobenzoate as a RAFT agent, after a pretreatment to affix the RAFT agent onto
the fibers with a silane.
Silk fibers modified with the coupling agent 3-(trimethoxysilyl) propyl methacrylate were grafted by Buga et al. (2015) from methyl methacrylate and tributylsilyl
methacrylate using 2-cyanoprop-2-yl dithiobenzoate as a RAFT agent. Yang et al.
(2013) grafted silk fibers with N,N-dimethylacrylamide using macromolecular
RAFT agents synthesized from acrylic acid, styrene, n-butyl acrylate and 2-(((dodecylsulfanyl) carbonothioyl) sulfanyl) propanoicacid to allow tuning of the radical
reactivity by control of the macromolecular composition.
The literature also reports that ramie fibers have been first modified with
2- bromisobutyryl bromide and carbon disulfide to produce 2-dithiobenzoyl isobutyrate moieties and then grafted with methyl acrylate, methyl methacrylate, styrene
and p-chlorostyrene using 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as a RAFT
agent (Chen et al. 2009; Yi et al. 2010). A similar procedure for grafting from
trifluoroethyl methacrylate onto ramie fibers in supercritical carbon dioxide was
carried out by Liu et al. (2010).
3.2.4 Polymer Deposition
Polymer deposition is another method for surface modifications of fibrous polymers
with other polymers, and also includes ‘grafting-to’ approaches. Günay et al.
(2017b, b) found that a conjugation with cyclic polypeptides increases the deposition of polymeric treatment agents based on poly(hydroxypropyl methacrylamide),
poly(styrene-co-acrylic acid) and polyurethane, onto cellulose fibers and proteins,
A. P. Manian et al.