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monomers in the oxygen-metal bond through electron rearrangement. Below we list
some selected examples of this method.
Başaran and Oral (2018) functionalized gelatin nanofibers by grafting poly(εcaprolactone) via ROP of the monomers using Sn(IV) isopropoxide as an initiator,
and with the amine groups of gelatin acting as co-initiators. Poly(ε-caprolactone)
and poly(L-lactic acid) have also been grafted from cellulose and micro-fibrillated
cellulose via ROP, using Sn(II) 2-ethylhexanoate as catalyst and benzyl alcohol as
co-initiator (Carlmark et al. 2012; Lönnberg et al. 2006; Lönnberg et al. 2008). This
method also produced good results in grafting wheat straw fibers (Kellersztein et al.
2016). It has also been shown that greater grafting efficiencies can be obtained if
cellulose is first modified to increase the density of available hydroxyl groups, by
agents such as xyloglucan derivatives or 2,2-bis(hydroxymethyl)propionic acid
(Lönnberg et al. 2006; Yeo and Hwang 2017). Epoxidized soybean oil, commonly
used as a plasticizer, has also been grafted from cellulose fibers in n-hexane using
tin chloride as a catalyst (Huang et al. 2017). Sisal fibers have also been modified by
grafting L-lactide in toluene using Sn(II) 2-ethylhexanoate as a catalyst (Ye et al.
2015; Jiang et al. 2016; Ye et al. 2017). The technique has also been employed for
the creation of hyperbranched polymers onto cellulose by grafting 3-methyl-3oxetanoethanol in methylene chloride using boron diethyl trifluoride etherate as an
initiator in a nitrogen atmosphere at 0 ° C (Yang et al. 2011).
3.2.3.3 Radical Polymerization
A dynamic equilibrium is established in the controlled/living radical polymerization, between the active and dormant states of the propagating radicals, which
extend their useful life to approx. 1 h, thus allowing greater control over polymerization of the added monomers (Matyjaszewski and Spanswick 2005; Braunecker
and Matyjaszewski 2007; Badri et al. 2012). Some common methods for achieving
equilibrium are described below (Braunecker and Matyjaszewski 2007; Barbey
et al. 2009; Zoppe et al. 2017), citing some selected examples of each:
3.2.3.3.1 Atom Transfer Radical Polymerization (ATRP)
This method is based on a reversible redox exchange of a halogen atom between a
transition metal complex and polymers capped with an alkyl halide end-group. The
transfer of the halogen atom to the metal complex produces a carbon-centered radical at the polymer chain end which activates the chain propagation, while the reverse
process converts the chain end into a dormant state. The metal complexes are commonly Cu compounds, and the alkyl halides are generally bromine compounds. The
advantages are that this method can be used with a variety of functional groups and
is relatively robust against impurities and residual oxygen, but a disadvantage is the
potential for residual amounts of transition metal in substrates, which can limit the
potential applications of these products.
A. P. Manian et al.
monomers in the oxygen-metal bond through electron rearrangement. Below we list
some selected examples of this method.
Başaran and Oral (2018) functionalized gelatin nanofibers by grafting poly(εcaprolactone) via ROP of the monomers using Sn(IV) isopropoxide as an initiator,
and with the amine groups of gelatin acting as co-initiators. Poly(ε-caprolactone)
and poly(L-lactic acid) have also been grafted from cellulose and micro-fibrillated
cellulose via ROP, using Sn(II) 2-ethylhexanoate as catalyst and benzyl alcohol as
co-initiator (Carlmark et al. 2012; Lönnberg et al. 2006; Lönnberg et al. 2008). This
method also produced good results in grafting wheat straw fibers (Kellersztein et al.
2016). It has also been shown that greater grafting efficiencies can be obtained if
cellulose is first modified to increase the density of available hydroxyl groups, by
agents such as xyloglucan derivatives or 2,2-bis(hydroxymethyl)propionic acid
(Lönnberg et al. 2006; Yeo and Hwang 2017). Epoxidized soybean oil, commonly
used as a plasticizer, has also been grafted from cellulose fibers in n-hexane using
tin chloride as a catalyst (Huang et al. 2017). Sisal fibers have also been modified by
grafting L-lactide in toluene using Sn(II) 2-ethylhexanoate as a catalyst (Ye et al.
2015; Jiang et al. 2016; Ye et al. 2017). The technique has also been employed for
the creation of hyperbranched polymers onto cellulose by grafting 3-methyl-3oxetanoethanol in methylene chloride using boron diethyl trifluoride etherate as an
initiator in a nitrogen atmosphere at 0 ° C (Yang et al. 2011).
3.2.3.3 Radical Polymerization
A dynamic equilibrium is established in the controlled/living radical polymerization, between the active and dormant states of the propagating radicals, which
extend their useful life to approx. 1 h, thus allowing greater control over polymerization of the added monomers (Matyjaszewski and Spanswick 2005; Braunecker
and Matyjaszewski 2007; Badri et al. 2012). Some common methods for achieving
equilibrium are described below (Braunecker and Matyjaszewski 2007; Barbey
et al. 2009; Zoppe et al. 2017), citing some selected examples of each:
3.2.3.3.1 Atom Transfer Radical Polymerization (ATRP)
This method is based on a reversible redox exchange of a halogen atom between a
transition metal complex and polymers capped with an alkyl halide end-group. The
transfer of the halogen atom to the metal complex produces a carbon-centered radical at the polymer chain end which activates the chain propagation, while the reverse
process converts the chain end into a dormant state. The metal complexes are commonly Cu compounds, and the alkyl halides are generally bromine compounds. The
advantages are that this method can be used with a variety of functional groups and
is relatively robust against impurities and residual oxygen, but a disadvantage is the
potential for residual amounts of transition metal in substrates, which can limit the
potential applications of these products.
A. P. Manian et al.