353
A-B n -type copolymer; the latter type contains epichlorohydrin-rich domains that are
hydrophilic by nature with an amorphous structure. This was demonstrated using
NMR data (Crini et al. 1998b; Bertini et al. 1999) and later confirmed by the Spanish
group of Professor José Ramon Isasi at Navarra University (Romo et al. 2004, 2006,
2008; García-Zubiri et al. 2006; Vélaz et al. 2007).
At the time, in accordance with Szejtli’s results, our group also reported that it
was important to select the optimal synthesis conditions to obtain the desired product characteristics, such as the degree of swelling and cyclodextrin content (Shao
et al. 1996; Vecchi et al. 1998; Crini et al. 1998a). By varying the synthesis conditions, for example, the amounts of the different reagents, the molar ratio of cyclodextrin to epichlorohydrin, the NaOH concentration, the reaction temperature, and
the reaction time, it was possible to induce structural modifications in the hydrogel
networks in terms of surface area and porosity and also to obtain gels or beads with
different cyclodextrin contents (Crini et al. 1998a, b). We have reported that a high
polymerization temperature promoted a high degree of polymer swelling. The introduction of rigid structures into a material has been beneficial to create porosity and
has increased the surface area, as well as the co-presence of an organic solvent during synthesis. Later, similar conclusions were reported by Professor Isasi (Romo
et al. 2004, 2006, 2008; García-Zubiri et al. 2006; Vélaz et al. 2007), by the Turkish
group of Professor Mustafa Yilmaz at Selçuk University (Yilmaz Ozmen and Yilmaz
2007, 2008), and by the Canadian group of Professor Lee D. Wilson at the University
of Saskatchewan (Mohamed et al. 2010, 2012; Pratt et al. 2010; Wilson et al. 2010).
The cross-linking step has always been the subject of debate in the literature.
Two “schools of thought” have been established (Crini 2005a; Morin-Crini and
Crini 2013): one promoting a low cross-linking leading to hydrogel-type products
and the other promoting a high cross-linking leading to organic bead-type products.
However, as Professor Szejtli has pointed out, this distinction may result from different end uses. For wastewater treatment, gel-type systems are appropriate but not
for use in high-pressure chromatography, as the particles must have some mechanical resistance (Szejtli 1982, 1988).
8.2.2 NMR Characterization
The mechanism described in Fig. 8.5 was studied in detail by Professor Bernard
Sébille (Université de Paris XII, France) in 1997 for water-soluble epichlorohydrincross- linked cyclodextrin polymers (Renard et al. 1997). The same year, our group
demonstrated for the first time the structure of water-insoluble ECP polymers by
NMR spectroscopy. These results were presented at the IXth European Carbohydrate
Symposium at Utrecht (The Netherlands, 6–11 July 1997) and published 1 year later
in the journal Carbohydrate Research (Crini et al. 1998b). Using cross- polarization
magic angle spinning with dipolar decoupling (CPMAS) and high- resolution magic
angle spinning (HRMAS) spectra, we demonstrated that, in the materials, two kinds
of structures existed with different molecular mobility: cyclodextrin cross-linked by
8 Water-Insoluble Cyclodextrin-Epichlorohydrin Polymers
A-B n -type copolymer; the latter type contains epichlorohydrin-rich domains that are
hydrophilic by nature with an amorphous structure. This was demonstrated using
NMR data (Crini et al. 1998b; Bertini et al. 1999) and later confirmed by the Spanish
group of Professor José Ramon Isasi at Navarra University (Romo et al. 2004, 2006,
2008; García-Zubiri et al. 2006; Vélaz et al. 2007).
At the time, in accordance with Szejtli’s results, our group also reported that it
was important to select the optimal synthesis conditions to obtain the desired product characteristics, such as the degree of swelling and cyclodextrin content (Shao
et al. 1996; Vecchi et al. 1998; Crini et al. 1998a). By varying the synthesis conditions, for example, the amounts of the different reagents, the molar ratio of cyclodextrin to epichlorohydrin, the NaOH concentration, the reaction temperature, and
the reaction time, it was possible to induce structural modifications in the hydrogel
networks in terms of surface area and porosity and also to obtain gels or beads with
different cyclodextrin contents (Crini et al. 1998a, b). We have reported that a high
polymerization temperature promoted a high degree of polymer swelling. The introduction of rigid structures into a material has been beneficial to create porosity and
has increased the surface area, as well as the co-presence of an organic solvent during synthesis. Later, similar conclusions were reported by Professor Isasi (Romo
et al. 2004, 2006, 2008; García-Zubiri et al. 2006; Vélaz et al. 2007), by the Turkish
group of Professor Mustafa Yilmaz at Selçuk University (Yilmaz Ozmen and Yilmaz
2007, 2008), and by the Canadian group of Professor Lee D. Wilson at the University
of Saskatchewan (Mohamed et al. 2010, 2012; Pratt et al. 2010; Wilson et al. 2010).
The cross-linking step has always been the subject of debate in the literature.
Two “schools of thought” have been established (Crini 2005a; Morin-Crini and
Crini 2013): one promoting a low cross-linking leading to hydrogel-type products
and the other promoting a high cross-linking leading to organic bead-type products.
However, as Professor Szejtli has pointed out, this distinction may result from different end uses. For wastewater treatment, gel-type systems are appropriate but not
for use in high-pressure chromatography, as the particles must have some mechanical resistance (Szejtli 1982, 1988).
8.2.2 NMR Characterization
The mechanism described in Fig. 8.5 was studied in detail by Professor Bernard
Sébille (Université de Paris XII, France) in 1997 for water-soluble epichlorohydrincross- linked cyclodextrin polymers (Renard et al. 1997). The same year, our group
demonstrated for the first time the structure of water-insoluble ECP polymers by
NMR spectroscopy. These results were presented at the IXth European Carbohydrate
Symposium at Utrecht (The Netherlands, 6–11 July 1997) and published 1 year later
in the journal Carbohydrate Research (Crini et al. 1998b). Using cross- polarization
magic angle spinning with dipolar decoupling (CPMAS) and high- resolution magic
angle spinning (HRMAS) spectra, we demonstrated that, in the materials, two kinds
of structures existed with different molecular mobility: cyclodextrin cross-linked by
8 Water-Insoluble Cyclodextrin-Epichlorohydrin Polymers