Synthesis and radical polymerisation of methacrylic monomers with crown ethers or their dipodal counterparts in the pendant structure

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.06.004

The synthesis and radical polymerisation of methacrylic monomers with benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, and their dipodal counterparts in the ester residue is described. The radical polymerisation of the monomers in solution was carried out at different temperatures, and the polymerisation kinetics curves were obtained by direct measurement of the instantaneous monomer concentrations by nuclear magnetic resonance spectroscopy (NMR). Thus, the polymerisation rate parameter (2fk_p/〈k _t〉^1/2), along with the polymer stereoregularity, were obtained in terms of the molar fractions of meso and racemo diads and of syndiotactic, isotactic and heterotactic triads. The interaction of the polymers with cations was studied using polymer networks as solid phases in the solid-liquid extraction of lanthanide cations from both organic and aqueous media.

Full text of DOI:10.1016/j.reactfunctpolym.2011.06.004

Reactive & Functional Polymers 71 (2011) 948–957
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and radical polymerisation of methacrylic monomers with crown
ethers or their dipodal counterparts in the pendant structure
⇑
Jimena Rey, Félix Clemente García, José Miguel García
Departamento de Química, Facultad de Ciencias, Universidad de Burgos, Plaza de Misael Bañuelos s/n, 09001 Burgos, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 April 2011
Received in revised form 15 June 2011
Accepted 19 June 2011
Available online 24 June 2011
The synthesis and radical polymerisation of methacrylic monomers with benzo-12-crown-4, benzo-15-
crown-5, benzo-18-crown-6, and their dipodal counterparts in the ester residue is described. The radical
polymerisation of the monomers in solution was carried out at different temperatures, and the polymer-
isation kinetics curves were obtained by direct measurement of the instantaneous monomer concentra-
tions by nuclear magnetic resonance spectroscopy (NMR). Thus, the polymerisation rate parameter
½
(2fkp/hkti ), along with the polymer stereoregularity, were obtained in terms of the molar fractions of
Keywords:
meso and racemo diads and of syndiotactic, isotactic and heterotactic triads. The interaction of the poly-
mers with cations was studied using polymer networks as solid phases in the solid–liquid extraction of
lanthanide cations from both organic and aqueous media.
Acrylic polymers
Polymethacrylates
Crown ethers
Podands
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
crosslinked membranes with gel behaviour [36]. In this work, we
expand our studies concerning polymers with crown ether and
Acrylic polymers belong to one of the most important families
of polymers, both from an industrial and from an academic point
of view. Regarding the latter, intermediates with the desired chem-
ical structure (having an alcohol or an amino group) are straight-
forward to prepare from an organic point of view, and they can
be easily transformed into (meth)acrylates or (meth)acrylamides.
These compounds can then be converted into polymers by conven-
tional or living solution radical polymerisation to render homo-
polymers or copolymers with random or segmented structures
[1–16].
Since the discovery of crown ethers [17,18], these compounds
have received significant attention because of their ability to estab-
lish weak, but important, interactions with charged species
through the formation of multi-highly directional ion–dipole inter-
actions between a cation and the ether groups of the crown moiety
[19,20]. These interactions were thought to resemble the impor-
tant interactions in nature, such as the molecular recognition of en-
zymes, antigen/antibody recognition, the double helix structure,
and membrane transport in cells, among others [21–26].
linear oxyethylene sequence, or podands, host motifs to polymeth-
acrylates with benzo-crown subunits (benzo-12-crown-4, benzo-
15-crown-5, and benzo-18-crown-6) in the ester residue. Their
dipodal open chain counterparts were also studied. Thus, we
describe below the synthesis of monomers, their polymerisation
and polymerisation kinetics, and interaction of the polymers with
cations through solid–liquid extraction of lanthanide cations from
aqueous and organic media. We have chosen the lanthanide ions to
test the ability of these polymers to interact with cations because
we have previously determined the interaction of these cations
with polymethacrylates containing a similar, but more flexible,
pendant aliphatic crown receptor motif [34,35].
2. Experimental section
2.1. Materials
All materials and solvents used for the synthesis of the mono-
mers were commercially available, and they were used as received
unless otherwise indicated. Ethyl 3,4-dihydroxybenzoate was pre-
pared by esterification of 3,4-dihydroxybenzoic acid with ethanol
We previously studied different polymers containing crown
ethers, along with potential applications related to their ability to
interact with cations, such as water and organic insoluble aromatic
polyamides [27–32], water soluble polymethacrylates [33–35], and
[27].
oxy)ethane, 1,11-dichloro-3,6,9-trioxaundecane, 1,14-dichloro-
3,6,9,12-tetraoxatetradecane], -chlorooligo(ethylene oxide)s, 1-
a-x-Dichlorooligo(ethylene oxide)s, [1,2-bis(2-chloroeth-
x
chloro-3,6-dioxaoctane, 1-chloro-3,6,9-trioxaundecane, and eth-
oxyethyl tosylate were synthesised and purified according to pre-
viously described procedures [37]. 4-Ethoxycarbonyl-benzo-12-
⇑
Corresponding author. Tel.: +34 947 25 80 85; fax: +34 947 25 88 31.
E-mail address: jmiguel@ubu.es (J.M. García).
URL: http://www2.ubu.es/quim/quimorg/polimeros/polimeros.htm (J.M. García).
1381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.06.004

J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
949
crown-4, 4-Ethoxycarbonyl-benzo-15-crown-5,4-Ethoxycarbonyl-
benzo-18-crown-6, ethyl 3,4-bis(2-ethoxyethoxy)benzoate, ethyl
3,4-bis-[2-(2-ethoxyehtoxy)ethoxy]benzoate, and ethyl 3,4-bis-
(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)benzoate were prepared
and characterised by the procedure of Calderon et al. [27–29].
2,20-Azobis(isobutyronitrile) (AIBN, Fluka, 98%) was recrystallised
from methanol and dried under high vacuum at room temperature
prior to use.
2.2.1.4. 3,4-Bis(2-ethoxyethoxy)phenylmethanol. Rf: 0.40. (AcOEt).
Brown oil.
1H NMR (400 MHz, CDCl3): 6.88 (s; 1H; ArH); 6.82 (s; 2H;
2ꢀArH); 4.52 (s; 2H; HOCH2); 4.11–4.05 (m; 4H; 2ꢀOCH2);
3.80–3.73 (m; 4H; 2ꢀOCH2); 3.56 (c; J = 7.0 Hz; 4H; 2ꢀOCH2
CH3); 2.67 (s; 1H; HOCH2); 1.19 (2t; J = 7.0 Hz; 6H; 2ꢀOCH2
CH3).
13C NMR (100.6 MHz, CDCl3): 149.01; 148.24; 134.72; 120.02;
114.72; 114.57; 113.60; 68.98; 68.74; 66.82; 64.91; 64.80; 15.20.
EI-LRMS (m/z, rel. int.): 284 (61), 212 (10), 166 (28), 140 (12), 73
(100), 45 (92).
2.2. Synthesis of the monomers
The synthetic route followed to prepare the monomers is de-
picted in Schemes 1 and 2. To obtain the monomer (Scheme 2), it
was necessary to prepare different intermediates (Scheme 1),
which were synthesised according to the following procedures.
2.2.1.5. 3,4-Bis-[2-(2-ethoxyehtoxy)ethoxy]phenylmethanol. Rf: 0.20.
(AcOEt). Brown oil.
1H NMR (400 MHz, CDCl3): 6.94 (s; 1H; ArH); 6.85 (s; 2H;
2ꢀArH); 4.55 (s; 2H; HOCH2); 4.17–4.10 (m; 4H; 2ꢀOCH2); 3.87–
3.80 (m; 4H; 2ꢀOCH2); 3.74–3.66 (m; 4H; 2ꢀOCH2); 3.61–3.55
(m; 4H; 2ꢀOCH2); 3.51 (c; J = 7.0 Hz; 4H; 2ꢀOCH2CH3); 2.21 (s;
1H; HOCH2); 1.19 (2t; J = 7.0 Hz; 6H; 2ꢀOCH2CH3).
13C NMR (100.6 MHz, CDCl3): 148.99; 148.37; 134.64; 120.14;
114.66; 113.80; 70.94; 70.89; 70.00; 69.95; 69.94; 69;80; 69;00;
68.82; 66.73; 65.03; 65.01; 15.24; 15.22.
2.2.1. Intermediates
The hydroxymethylbenzene derivatives 9a–c and 10a–c were
synthesised by the same general method (Scheme 1). The synthesis
of 4-hydroxymethyl-(benzo-12-crown-4) (9a) is described as an
illustrative example.
2.2.1.1. 4-Hydroxymethyl-(benzo-12-crown-4) (9a). In a round bot-
tom flask fitted with a mechanical stirrer and a condenser under
nitrogen atmosphere, 150 mL of THF was cooled to 0 °C. Next,
3.8 g (0.1 mol) of LiAlH4 was dissolved under stirring. Then, a solu-
tion of 4-ethoxycarbonyl-benzo-12-crown-4 in 50 mL of THF was
added dropwise. Subsequently, the reaction mixture was heated
to reflux, and the disappearance of the ester was followed by
TLC. The solution was then cooled, poured cautiously into ice
water, and treated with a few drops of HCl. The water/THF solution
was then filtered through celite, and the THF was eliminated on a
rotary evaporator. The water solution was extracted with CH2Cl2
(3 ꢀ 30 mL), dried with magnesium sulphate, and vacuum concen-
trated to give a yellowish oil.
EI-LRMS (m/z, rel. int.): 372 (2), 166 (13), 117 (100), 89 (9), 73
(86), 45 (82).
2.2.1.6. 3,4-Bis-(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)phenylmetha-
nol. Rf: 0.16. (AcOEt). Brown oil.
1H NMR (400 MHz, CDCl3): 6.99 (s; 1H; ArH); 6.87 (s; 2H;
2ꢀArH); 4.58 (s; 2H; HOCH2); 4.21–4.11 (m; 4H; 2ꢀOCH2); 3.87–
3.81 (m; 4H; 2ꢀOCH2); 3.75–3.69 (m; 8H; 4ꢀOCH2); 3.68–3.61
(m; 4H; 2ꢀOCH2); 3.60–3.55 (m; 4H; 2ꢀOCH2); 3.51 (c;
J = 7.0 Hz; 4H; 2ꢀOCH2CH3); 1.84 (s; 1H; HOCH2); 1.19 (2t;
J = 7.0 Hz; 6H; 2ꢀOCH2CH3).
13C NMR (100.6 MHz, CDCl3): 149.13; 148.55; 134.64; 120.30;
114.79; 114.12; 70.92; 70.79; 69.94; 69.87; 69.03; 68.93; 66.78;
65.54; 15.27.
Rf: 0.11 (AcOEt).
1H NMR (400 MHz, CDCl3): 6.97 (d; J = 1.61 Hz; 1H; ArH); 6.92–
6.90 (m; 2H; 2ꢀArH); 4.57 (s; 2H; HOCH2); 4.16–4.11 (m; 4H;
2ꢀOCH2); 3.85–3.70 (m; 4H; 2ꢀOCH2); 3.77 (s; 4H; OCH2CH2O);
2.12 (s; 1H; OH).
EI-LRMS (m/z, rel. int.): 460 (1), 208 (11), 207 (53), 161 (23), 117
(46), 73 (100), 45 (63).
13C NMR (100.6 MHz, CDCl3): 150.54; 149.70; 135.95; 121.09;
118.11; 116.58; 71.92; 71.37; 71.13; 71.02; 69.86; 64.66.
EI-LRMS (m/z, rel. int.): 254 (100), 165 (41), 166 (40), 151 (52),
137 (84), 110 (25), 45 (27).
2.2.2. Monomers
The methacrylate monomers 11a–c and 12a–c were synthes-
ised by the same general method (Scheme 2). The synthesis of
4-(methacryloxymethyl)-benzo-12-crown-4 is described as an
illustrative example. The reaction solvent was ethyl ether or
dichloromethane for the preparation of methacrylates with pen-
dant podand or crown ether substructures, respectively.
2.2.1.2. 4-Hydroxymethyl-(benzo-15-crown-5). M.p.: 43–45 °C.
1H NMR (400 MHz, CDCl3): 6.82 (d; J = 1.6 Hz; 1H; ArH); 6.80
(dd; J = 1.6 and 8 Hz; 1H; ArH); 6.74 (d; J = 8 Hz; 1H; ArH); 4.50
(s; 2H; HOCH2); 4.08–4.02 (m; 4H; 2ꢀOCH2); 3.90–3.81 (m; 4H;
2ꢀOCH2); 3.69 (s; 8H; 2ꢀOCH2CH2O); 2.95 (s; 1H; HOCH2).
13C NMR (100.6 MHz, CDCl3): 148,97; 148.22; 134.52; 119.68;
113.57; 112.63; 70.84; 70.34; 69.49; 68.89; 68.59; 64.76.
EI-LRMS (m/z, rel. int.): 298 (29), 166 (82), 165 (58), 151 (56),
149 (52), 137 (100), 45 (40).
2.2.2.1.
4-(Methacryloxymethyl)-benzo-12-crown-4. 4-Hydroxy-
methyl-(benzo-12-crown-4) (7.4 g, 23 mmol) and 7.7 g (46 mmol)
of Et3N were dissolved in 50 mL of dichloromethane in a 100 mL
round bottom flask fitted with a condenser under a nitrogen blan-
ket and magnetic stirring. The solution was then cooled to 0 °C, and
4.9 g (46 mmol) of methacryloyl chloride was added dropwise.
After the addition, the cooling was discontinued, and the system
was stirred for a further 24 h. Then, the mixture was extracted
repeatedly with water, the organic layer was dried with magne-
sium sulphate, and the solvent was removed under vacuum. To
achieve high purity, the product was purified by flash column chro-
matography using ethyl acetate/hexane (1:1) as the mobile phase
and silica gel (230–400 mesh) as the stationary phase, affording
a colourless solid.
2.2.1.3. 4-Hydroxymethyl-(benzo-18-crown-6). Rf: 0.03. (AcOEt).
White wax.
1H NMR (400 MHz, CDCl3): 6.82 (d; J = 2.0 Hz; 1H; ArH); 6.80
(dd; J = 2.0 and 10.4 Hz; 1H; ArH); 6.77 (d; J = 10.4 Hz; 1H; ArH);
4.50 (s; 2H; HOCH2); 4.08–4.03 (m; 4H; 2ꢀOCH2); 3.90–3.81 (m;
4H; 2ꢀOCH2); 3.72–3.68 (m; 4H; 2ꢀOCH2); 3.67–3.63 (m; 4H;
2ꢀOCH2); 3.62 (s; 4H; OCH2CH2O); 2.95 (s; 1H; HOCH2).
13C NMR (100.6 MHz, CDCl3): 148.76; 148.01; 134.50; 119.62;
113.57; 112.63; 70.67; 70.60; 70.57; 69.52; 68.92; 68.69; 64.70.
EI-LRMS (m/z, rel. int.): 342 (22), 166 (50), 165 (38), 164 (59),
163 (50), 150 (45), 149 (43), 137 (44), 45 (66), 43 (43), 28 (100).
M.p.: 69–71 °C.
1H NMR (400 MHz, CDCl3): 6.97 (d; J = 1.8 Hz; 1H; ArH); 6.94
(dd; J = 1.8 and 8 Hz; 1H; ArH); 6.91 (d; J = 8 Hz; 1H; ArH); 6.15–
6.06 (m; 1H; @CHH); 5.56–5.51 (m; 1H; @CHH); 5.06 (s; 2H;

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J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
CO2H
CO2Et
EtOH
H2SO4 (cat)
OH
OH
OH
OH
1
2 (98 %)
TsCl, NaOH
THF:H2O
HO
HO
OH
OH
TsO
OTs
Cl
O
O
2
2
4a (95 %)
3a
Cl
SOCl2, DMF (cat)
Hx
O
O
n
n
4b (94 %), 4c (89 %)
n = 3 (3b), 4 (3c)
TsCl, NaOH
THF:H2O
HO
TsO
O
O
5a
6a (85 %)
HO
Cl
SOCl2, DMF (cat)
Hx
O
O
n
n
6b (94 %), 6c (89 %)
n = 2 (5b), 3 (5c)
CO2Et
CH2OH
CO2Et
K2CO3
X
DMF
LiAlH4
THF
+
X
O
n
O
O
OH
4a (n=2, X=OTs),
4b (n=3, X=Cl),
4c (n=4, X=Cl)
O
O
n
n
OH
O
O
2
O
O
7a (33 %), 7b (65 %), 7c (60 %)
9a (70 %), 9b (72 %), 9c (77 %)
CH2OH
CO2Et
CO2Et
X
K2CO3
DMF
LiAlH4
THF
+
O
O
O
n
O
O
O
n
n
OH
O
O
6a (n=1, X=OTs),
6b (n=2, X=Cl),
6c (n=3, X=Cl)
OH
2
O
n
n
8a (88 %), 8b (95 %), 8c (95 %)
10a (68 %), 10b (75 %), 10c (83 %)
Scheme 1. Sequence for the synthesis of monomer intermediates.
OCH2Ar); 4.20–4,10 (m; 4H; 2ꢀOCH2); 3.85–3.80 (m; 4H;
2ꢀOCH2); 3.75 (s; 4H; OCH2CH2O); 1.93 (dd; J = 0.9 and 1.5 Hz;
3H; CH3).
EI-LRMS (m/z, rel. int.): 322 (65), 149 (100), 137 (40), 69 (52), 45
(30), 43 (23), 41 (38).
13C NMR (100,6 MHz, CDCl3): 167.26; 150.57; 150.51; 136.22;
130.56; 125.57; 122.81; 118.24; 117.87; 71.80; 71.72; 71.12;
69.87; 66.15; 18.41.
2.2.2.2. 4-(Methacryloxymethyl)-benzo-15-crown-5. M.p.: 72–74 °C.
1H NMR (400 MHz, CDCl3): 6.92–6.84 (m; 2H; ArH); 6.80 (d;
J = 8 Hz; 1H; ArH); 6.11–6.07 (m; 1H; @CHH); 5.56–5.50 (m; 1H;

J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
951
crown ether monomers
O
CH2OH
O
O
O
Cl
O
O
Et3N, CH2Cl2
n
O
O
n
O
O
O
n = 1 (9a), 2 (9b), 3 (9c)
n
1
2
3
monomer code 11a (68 %) 11b (70 %) 11c (63 %)
podand monomers
O
CH2OH
O
O
O
Cl
O
n
Et3N, Et2O
O
O
O
n
O
O
n
O
n
n = 1 (10a), 2 (10b), 3 (10c)
n
1
2
3
monomer code 12a (60 %) 12b (85 %) 12c (65 %)
Scheme 2. Sequence for the synthesis of the monomers.
@CHH); 5.06 (s; 2H; OCH2Ar); 4.18–4.01 (m; 4H; 2ꢀOCH2); 3.96–
3.81 (m; 4H; 2ꢀOCH2); 3.72 (s; 8H; 2ꢀOCH2CH2O); 1.91 (dd;
J = 0.9 and 1.5 Hz; 3H; CH3).
2ꢀOCH2); 3.59 (2c; J = 7.0 Hz; 4H; OCH2CH3); 1.94 (dd; J = 0.9
and 1.7 Hz; 3H; CH3); 1.21 (2t; J = 7.0 Hz; 6H; 2ꢀOCH2CH3).
13C NMR (100.6 MHz, CDCl3): 167.34; 149.10; 149.02; 136.33;
129.40; 125.80; 121.93; 121.79; 115.17; 11.58; 114.47; 69.01;
68.88; 66.89; 66.40; 18.44; 15.29.
13C NMR (100.6 MHz, CDCl3): 167.27; 149.11; 149.04; 1336.24;
129.07; 125.77; 121.57; 114.30; 113.66; 71.09; 70.45; 69.55;
69.40; 69.02; 66.39; 18.39.
EI-LRMS (m/z, rel. int.): 352 (59), 149 (18), 73 (91), 69 (24), 45
(100), 41 (10).
EI-LRMS (m/z, rel. int.): 366 (95), 367 (18), 189 (23), 165 (20),
164 (23), 149 (100), 148 (21), 137 (37), 69 (22).
2.2.2.5. 3,4-Bis-[2-(2-ethoxyehtoxy)ethoxy] benzylmethacrylate. Rf:
0.47 (AcOEt). Colourless oil.
2.2.2.3. 4-(Methacryloxymethyl)-benzo-18-crown-6. Rf: 0.09. (AcOEt).
Brown oil.
1H NMR (400 MHz, CDCl3): 6.94–6.87 (m; 1H; ArH); 6.85 (d;
J = 8.2 Hz; 1H; ArH); 6.12–6.06 (m; 1H; @CHH); 5.57–5.49 (m;
1H; @CHH); 5.06 (s; 2H; OCH2Ar); 4.18–4.11 (m; 4H; 2ꢀOCH2);
3.88–3.79 (m; 4H; 2ꢀOCH2); 3.73–3.66 (m; 4H; 2ꢀOCH2); 3.61–
3.54 (m; 4H; 2ꢀOCH2); 3.49 (2c; J = 7.0 Hz; 4H; OCH2CH3); 1.92
(dd; J = 1.0 and 1.5 Hz; 3H; CH3); 1.18 (t; J = 7.0 Hz; 6H;
2ꢀOCH2CH3).
1H NMR (400 MHz, CDCl3): 6.92–6.85 (m; 2H; ArH); 6.80 (d;
J = 8.5 Hz; 1H; ArH); 6.13–6.04 (m; 1H; @CHH); 5.58–5.47 (m;
1H; @CHH); 5.05 (s; 2H; OCH2Ar); 4.16–4.06 (m; 4H; 2ꢀOCH2);
3.92–3.83 (m; 4H; 2ꢀOCH2); 3.75–3.70 (m; 4H; 2ꢀOCH2); 3.69–
3.65 (m; 4H; 2ꢀOCH2); 3.62 (s; 4H; OCH2); 1.90 (dd; J = 0.9 and
1.5 Hz; 3H; CH3).
13C NMR (100.6 MHz, CDCl3): 167.24; 148.94; 148.86; 136.52;
129.31; 125.75; 121.70; 114.94; 114.40; 70.92; 69.91; 69.72;
68.92; 68.89; 66.67; 66.33; 18.38; 15.19.
13C NMR (100.6 MHz, CDCl3): 167.44; 149.12; 149.05; 136.42;
129.25; 125.95; 121.73; 114.53; 113.92; 71.03; 70.89; 69.77;
69.27; 66.55; 18.58.
EI-LRMS (m/z, rel. int.): 410 (16), 189 (18), 164 (21), 165 (22),
148 (20), 137 (19), 69 (45), 45 (46), 43 (34), 41 (24), 28 (31).
EI-LRMS (m/z, rel. int.): 440 (11), 149 (19), 117 (98), 73 (89), 69
(27), 59 (10), 45 (100).
2.2.2.6. 3,4-Bis-(2-(2-(2-ethoxyethoxy)ethoxy)ethoxy)benzyl methac-
rylate. Rf: 0.28 (AcOEt). Colourless oil.
2.2.2.4.
3,4-Bis(2-ethoxyethoxy)benzyl
methacrylate. Rf:
0.50
(AcOEt). Colourless oil.
1H NMR (400 MHz, CDCl3): 6.95–6.89 (m; 1H; ArH); 6.88 (d;
J = 8.3 Hz; 1H; ArH); 6.14–6.09 (m; 1H; @CHH); 5.59–5.53 (m;
1H; @CHH); 5.08 (s; 2H; OCH2Ar); 4.21–4.11 (m; 4H; 2ꢀOCH2);
3.89–3.81 (m; 4H; 2ꢀOCH2); 3.77–3.70 (m; 4H; 2ꢀOCH2); 3.69–
3.61 (m; 8H; 4ꢀOCH2); 3.61–3.55 (m; 4H; 2ꢀOCH2); 3.51 (c;
1H NMR (400 MHz, CDCl3): 6.95 (d; J = 1.8 Hz; 1H; ArH); 6.92
(dd; J = 1.8 and 8.2 Hz; 1H; ArH); 6.88 (d; J = 8.2 Hz; 1H; ArH);
6.15–6.08 (m; 1H; @CHH); 5.58–5.52 (m; 1H; @CHH); 5.08 (s;
2H; OCH2Ar); 4.18–4.11 (m; 4H; 2ꢀOCH2); 3.82–3.75 (m; 4H;

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J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
J = 7.0 Hz; 4H; OCH2CH3); 1.94 (dd; J = 1.0 and 1.5 Hz; 3H; CH3);
1.19 (t; J = 7.0 Hz; 6H; 2ꢀOCH2CH3).
tetramethylsilane (TMS) as the internal standard. A Varian GEMINI
200 NMR spectrometer with the temperature controlled at
0.05 °C was used to control the changes in monomer concentra-
tion during the polymerisation reactions. These experiments used
deuterated benzene as solvent and TMS as the internal standard.
The polymerisation kinetics experiments in solution were car-
ried out as follows: the monomers were dissolved in 5 mL of deu-
terated benzene to a concentration of 1 M and adding AIBN to a
concentration of 0.1 M. Then, 0.75 mL of this solution was intro-
duced into a 5 mm NMR tube after elimination of oxygen by bub-
bling nitrogen into the solution. The reaction was then carried out
between 50 and 70 °C. The kinetics of polymerisation was followed
by measuring changes in the monomer concentrations by NMR
spectroscopy. The area changes in the resonance signals corre-
sponding to the methylene protons of the double bond of the
methacrylic residue that appeared at 5.6 and 6.1 ppm were used
to determine the variation of monomer concentration. As an illus-
trative example, Fig. 1 shows the 1H NMR spectra corresponding to
the polymerisation of monomer 11c.
13C NMR (100.6 MHz, CDCl3): 167.49; 149.10; 149.05; 136.46;
129.51; 125.98; 121.91; 115.11; 114.60; 71.04; 70.88; 70.72;
70.02; 69.90; 69.04; 66.85; 66.54; 18.59; 15.37.
EI-LRMS (m/z, rel. int.): 528 (1), 161 (17), 73 (96), 69 (19), 59
(10), 45 (100).
2.3. Synthesis of the polymers
The linear polymethacrylates were prepared by conventional
radical polymerisation of the corresponding monomers in solution.
A 0.3 M or 0.7 M benzene solution of the monomers with crown
ether (11a–c) or podand (12a–c) moieties, respectively, were pre-
pared in a jacketed reactor. The solutions were deoxygenated by
nitrogen bubbling, AIBN was added to achieve a concentration of
0.003 M, and then the reaction was heated to 60 °C under a nitro-
gen blanket. The polymerisation was quenched when the conver-
sion was approximately 50%, followed gravimetrically with
aliquots taken periodically to avoid anomalous effects. The
quenching and isolation of the polymers was accomplished by low-
ering the temperature and precipitating in a mixture of ethyl ace-
tate/hexane (1:1) or pure hexane for polymers containing crown
ether or podands, respectively, in the pendant structure. The poly-
mer structures and codes are depicted in Scheme 3.
The crosslinked polymethacrylates, used in the solid–liquid
extraction experiments were prepared by means of bulk polymer-
isation of the corresponding monomers using 1% AIBN (by weight,
dissolved in acetonitrile) and 1 mol% crosslinker (ethylene glycol
dimethacrylate). Thus, the nominal crosslinking ration (NCR), i.e.,
the ratio between number of moles of the monomer to the cross-
linking agent, was 100. Acetonitrile was used as a solvent promoter
in a few cases. The solutions were thoroughly deoxygenated by
nitrogen bubbling, with the concomitant elimination of most of
the acetonitrile. Then, the solution was heated to 60 °C under a
nitrogen atmosphere for 5 h. Finally, the system was washed in
acetone, giving rise to an insoluble white powder.
The solid–liquid extraction of each target cation (La3+, Ce3+, Pr3+
,
Nd3+, Sm3+, Eu3+, Gd3+, and Tb3+ as their perchlorate salts was car-
ried out as follows: 10 mg of the proper crosslinked polymer was
shaken with 1 mL of a water or acetonitrile solution of the proper
cation series for a week at 25 °C (liquid phase). The molar ratio of
the overall cations in each cation series to crown subunits (poly-
meric structural units) was 1:1, and all of the cations of a series
were at the same concentration. After filtration, the concentration
of the cations in the aqueous phase was determined by inductively
coupled plasma mass spectrometry (ICP-MS, Agilent 7500i), and
direct information on the selectivity of polyamides toward metal
ions was obtained.
Low-resolution electron impact (LR-EI) mass spectra were ob-
tained at 70 eV on an Agilent 6890N mass spectrometer.
Gel Permeation Chromatography (GPC) analyses were carried
out by using PSS-GRAM columns of nominal pore size 30, 100
and 3000 Å. N,N-Dimethylformamide (DMF)/0.01 M LiBr was used
as solvent and the measurements were done at 70 °C with flow rate
of 1.0 mL/min, and using a RI detector. The columns were cali-
brated with narrow distribution standards of poly(methyl
methacrylate).
2.4. Measurements
The thermal properties of the polymers were determined
calorimetrically (DSC) with a Perkin-Elmer Pyris I calorimeter at
a heating rate of 10 °C minꢁ1 by measuring the glass transition
The NMR spectra of polymers were recorded on a Varian
INOVA 400 spectrometer operating at 399.92 MHz (1H) and
100.57 MHz (13C) using deuterated chloroform as solvent and
Scheme 3. Polymer structures and codes.

J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
953
a
g,h,i,k,l,m
p,j
b
O
X
O
c
e
f
d
g
t=0 s
O
j
i
O
O
3
h
t=242 s
t=410 s
t=740 s
t=1100 s
t=1520 s
t=2120 s
t=4382 s
O
k
l
3
m
p
d,e,f
a
7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2
c
b
δ, ppm
Fig. 1. 1H NMR spectra corresponding to the polymerisation kinetics experiment on
monomer 11c to give the polymethacrylate 13c (solvent: deuterated benzene;
temperature: 60 °C).
8
7
6
5
4
3
2
1
0
δ, ppm
l,m,p,r,s,t
a
c
temperature (Tg) at the onset of the separation of endotherms from
the baseline.
b
O
d
X
O
e
f
g
i
3. Results and discussion
l
q
O
h
j
O
k
p
3
m
q,v
e
O
3.1. Polymer synthesis and characterisation
r
s
O
The preparation of the monomers was carried out following
conventional organic chemistry methodology, as depicted in
Schemes 1 and 2. The preparation of the benzo-crown ethers and
their dipodal counterparts was achieved by cyclisation reactions
using the conventional Williamson ether synthesis from the
1,2-benzenediol derivative and the corresponding organohalide
giving rise to products with high yield and purity (7b–c and 8b–
c), except for the lower crown or dipodal compounds of the two
series. Regarding this point, the substitution of the organohalide
by the tosylate increased the yield of 7a from 20% to 33%. This yield
corresponded to the isolated product and was ꢂ30% higher than
the reported previously for other benzo-12-crown-4 derivatives
[38,39]. This improved yield could be achieved using high dilution,
but not templates. The preparation of 7a gave rise to a by-product
3
t
v
k,j
g,h,i,f
c
b
a
d
200 180 160 140 120 100 80
60
40
20
0
δ, ppm
Fig. 2. 1H and 13C NMR spectra (400 and 100.6 MHz, CDCl3) of polymer 14c.
ing classical, and previously described, assignment in other meth-
acrylic polymers [41–43], the resonance signals were attributed to
different tactic triads and pentads (in the case of the carbonylic
carbon, Fig. 4) from which the molar fractions of different configu-
rations were calculated. An average molar fraction of syndiotactic
dyads of 0.81 0.03 was obtained. Comparison with the values
for triad and pentad units indicated Bernoullian stereochemical
control [44]. This result was similar to that found for a wide set
of polymethacrylates obtained by radical polymerisation, indicat-
ing the predominance of syndiotactic over isotactic sequences
[45,46].
diester,
bis(4-ethoxycarbonyl-1,2-diphenylene)-24-crown-8,
which was eliminated by means of column chromatography. Inter-
estingly, the diester by-product was not detected in benzo-crown
ethers with higher oxyethylene sequences (7b–c). The subsequent
reduction of the esters (7a–c and 8a–c) to the alcohols (9b–c and
10b–c), and from there to the methacrylates (11a–c and 12b–c),
was easily accomplished with good yield. The methacrylates were
column purified to ensure high purity products.
Conventional radical solution polymerisation of the monomers
gave rise to polymers. The conversion was maintained around
50%, followed gravimetrically during polymerisation, to avoid
anomalous reactions usually observed at higher yields. The poly-
mer structures were confirmed by NMR, as depicted in Figs. 2
and 3 for polymers 14c and 13b, as illustrative examples. The aver-
age number molecular weight and molecular weight distribution
were Mn = 2.8 ꢀ 104, 2.1 ꢀ 104, 2.4 ꢀ 104, 3.2 ꢀ 104, 2.0 ꢀ 104,
3.3 ꢀ 104 g/mol, and Mw/Mn = 1.72, 1.81, 1.86, 1.91, 1.78, 1.89 for
polymers 13a, 13b, 13c, 14a, 14b, 14c, respectively. These results
are in accordance with those obtained by other researchers for
vinyl polymers with bulky side groups [40].
The values of Tgs of the linear polymers ranged between ꢁ90
and 55 °C, as depicted in Fig. 5 for all of the polymers. Interestingly,
the transition showed a huge dependence on the flexibility of the
pendant structure. Thus, the differences between series 14a–c
and 13a–c ranged from 57 to 79 °C because of the conformational
restrictions imposed by the alicycle in the former. In each series,
the increasing mobility of the oxyethylene sequences gave rise to
a decreased transition temperature. These data related well with
previously reported polymethacrylates containing
a lateral
methyl-12-crown-4 and its open chain counterpart, [poly(tetraeth-
yleneglycol monoethyl ether) methacrylate], with Tgs values of 35
and ꢁ48 °C, respectively [33–47]. Regarding the Tgs of the cross-
linked materials, they could not be detected by DSC. Nevertheless,
the crosslinking of polymer chains impairs the generalized chain
movement increasing this transition. For example, a polymer net-
work with a related structure, comprised of poly[2-(2-aminoeth-
oxyethanol) methacrylamide], and, NCR, had a glass transition
20 °C higher than the corresponding linear polymer.
The polymer microstructure was determined by 13C and 1H
NMR. The molar fractions of the diads and triads were determined
by measuring the relative peak areas corresponding to the signals
of CO, C, a-CH3, and CH2, as shown for polymer 13b in Fig. 4. Three
resonance signals appeared for each carbon, except the C@O that
had greater sensitivity to the stereochemical configuration. Follow-

954
J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
termination rate constants, respectively). In the equation, [M0] and
a
g,h,i,j
[M] are the initial and instantaneous concentrations of monomer,
respectively, [I0] is the initial concentration of initiator, and f is
the efficiency of the initiator. Eq. (1) is therefore a suitable equa-
O
b
X
O
c
½
½
tion to describe the polymerisation whenever (2f) kp/hkti re-
d
e
mains throughout the reaction.
g
f
O
h
!
ꢂ
ꢀ
ꢁꢃ
1=2
O
O
½M0ꢃ
½Mꢃ
2f½I0ꢃ
ꢁkdt
i
In
¼ 2kp
1 ꢁ exp
ð1Þ
O
ktkd
2
O
j
The variation of the monomer concentration throughout the
d,e,f
polymerisation reaction is depicted in Fig. 6 for monomer 11c at
temperatures ranging from 50 to 70 °C. The lines correspond to
the fitting of the data using Eq. (1).
From these data, the relationship to low conversions can be ex-
tracted when the concentration of the radical initiator was consid-
ered constant. Eq. (1) could then be transformed into the following
equation:
a
c
b
8
7
6
5
4
3
2
1
0
δ, ppm
a
c
l,m,p,q
e
d
O
b
!
X
1=2
O
½M0ꢃ
½Mꢃ
2f½I0ꢃkd
e
In
¼ kp
t
ð2Þ
kt
f
g
i
l
Thus, the least square adjustment of the time vs. ln([M0]/[M])
data gave rise to a straight line with a slope corresponding to
h
j
O
k
m
O
O
½
½
½
p
(2f) [I0] kp/hkti , as depicted in Fig. 7 for the polymerisation of
monomer 12a. From the slopes at time zero and the averaged val-
ues of kd for AIBN reported in the literature, [48–51] the values of
O
O
q
k,j
g,h,i,f
½
½
the rate parameter (2f) kp/hkti at different temperatures were
determined (Table 1). At high conversions, the so-called gel or Nor-
rish-Tromsdorff effect was not observed, a phenomenon previously
described in the polymerisation of methacrylates having short ali-
phatic oxyethylene sequences [45,46].
c
d
a
b
200 180 160 140 120 100 80
60
40
20
0
δ, ppm
½
½
The values of (2f) kp/hkti for all of the monomers were very
high, exceeding those corresponding to the methacrylate with
the aliphatic crown ether residue by almost twofold [52] and their
open chain methacrylates homologues by almost threefold [45,53].
Furthermore, the polymerisation rates for the monomers with less
bulky side groups (12a and 11a) resembled those observed in the
polymerisation of functional hydrophilic monomers such as 2-
hydroxyethylmethacrylate (HEMA) [33] and 2,3-dihydroxypropyl-
methacrylate [54]. Meanwhile, this parameter was much higher in
the monomers with bulkier groups (12b–c, 11b–c). Fig. 8 shows
the relationship of the monomer conversion at a given polymerisa-
tion time vs. side group bulkiness (i.e., the dependence of the rate
Fig. 3. 1H and 13C NMR spectra (400 and 100.6 MHz, CDCl3) of polymer 13b.
3.2. Kinetics of polymerisation
The data for radical polymerisation kinetics followed by 1H
NMR were analysed using Eq. (1), which is straightforwardly
derived from the classical radical polymerisation scheme by
assuming equal initiation and termination rates (i.e., the so-called
stationary state, where kd, is the rate constant for initiator decom-
position and kp and hkti are the overall averages of propagation and
rr
rr
rr
mr+rm
mr+rm
mr+rm
mm
mm
mm
179
178
177
176
175
46
45
44
56
54
52
rr
50
rr
mr+rm
mr+rm
mm
mm
22
20
18
16
14
1.2
0.8
0.4
Fig. 4. Molar fractions of tactic triads and diads in polymethacrylate 13b determined by NMR.

J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
955
Table 1
13b
13c
13a
Kinetic rate parameter for the polymerisation of the methacrylates in 1 M benzene
solution using an initiator concentration (AIBN) of 0.1 M. The last column lists the
values of kd used for the calculations.
60
40
½
½
½
a
(2f) kp/hkti (L molꢁ½ sꢁ½
)
20
T
(°C)
12a
12b
12c
11a
11b
11c
Referenceb kd ꢀ 106
0
(sꢁ1
)
-20
-40
-60
-80
-100
50
55
60
65
70
0.537 0.734 1.093
–
0.627 0.966 0.427
2.2
4.5
9.1
18.6
36.5
T
0.564 0.777 1.118 0.451 0.646 1.029 0.444
0.581 0.811 1.154 0.471 0.675 1.098 0.456
0.605 0.871 1.178 0.488 0.695 1.155 0.464
0.631 0.923 1.226 0.507 0.713 1.226 0.480
a
f is usually considered to be 0.6 for most systems.
Poly(hydroxymethyl-12-crown-4) methacrylate.
b
14b
14a
14c
Polymethacrylate
Fig. 5. Tgs of the polymethacrylates with crown ether moieties (j) and with
podand subgroups (d).
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
0
500
1000
1500
t, s
2000
2500
Fig. 8. Variation in monomer concentration with polymerisation time (12a (N), 12b
(d), 12c (j); 60 °C, [M0] = 1 mol Lꢁ1, [I0] = 0.1 mol Lꢁ1).
0
1000
2000
3000
4000
Fig. 6. Changes in the monomer concentration in the radical polymerisation of 11c
at 70 °C (H), 65 °C (ꢀ), 60 °C (N), 55 °C (d), 50 °C (j), [M0] = 1 mol Lꢁ1
, and
[I0] = 0.1 mol Lꢁ1). The lines correspond to the fitting of the data using Eq. (1).
1.2
12c
1.1
11c
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
1.0
0.9
12b
0.8
0.7
11b
12a
0.6
<
k
0.5
0.4
11a
12
2f
8
10
14
16
18
20
22
24
26
Side chain atoms
½
½
Fig. 9. Rate parameter (2f) kp/hkti vs. number of side chain atoms at a polymer-
isation temperature of 55 °C for monomers with alicyclic (d) and acyclic (j)
structures.
0
200 400 600 800 1000 1200 1400 1600
t, s
Fig. 7. Monomer concentration vs. time in the polymerisation of 12a at different
temperatures [70 °C (H), 65 °C (ꢀ), 60 °C (N), 55 °C (d), 50 °C (j)]. Polymerisation
conditions: [M0] = 1 mol Lꢁ1, [I0] = 0.1 mol Lꢁ1). The straight lines correspond to the
fitting of the data using a least square adjustment.
3.3. Solid–liquid extraction of cations from organic and aqueous media
The solid–liquid extraction technique is based on the extraction
of a chemical from solution with a solid phase. The extraction
effectiveness is based on physical interactions of the target chem-
ical in solution with the solid phase through the solid–liquid inter-
phase. Polymer networks take advantage of their solvent swelling
ability, sometimes giving rise to gels, easily allowing the solvated
target chemicals to reach the chemical subgroups within the poly-
mer structure. Interactions then take place by means of diffusion,
parameter on the number of oxyethylene sequences in crown and
dipodal containing monomers). This incremental change in the
polymerisation rate with increasing molecular weight of the meth-
acrylic monomers is usually found in radical polymerisation [55],
with steric effects playing a major role in this change, probably be-
cause of the decrease in hkti [56]. In our system, this behaviour can
be graphically observed in Fig. 9.

956
J. Rey et al. / Reactive & Functional Polymers 71 (2011) 948–957
Table 2
Solid–liquid extraction percentage (%E) of lanthanide cations in acetonitrile and aqueous solution (between brackets) using crosslinked methacrylates.a
Polymer
La3+
Ce3+
Pr3+
Nd3+
Sm3+
Eu3+
Gd3+
Tb3+
12(–)
24 (–)
15 (8)
12 (5)
18 (13)
35 (20)
13a
13b
13c
14a
14b
14c
8 (–)
6 (–)
7 (–)
5 (–)
7 (–)
9 (–)
9 (–)
23 (–)
17 (9)
12 (5)
19 (15)
37 (24)
21 (–)
62 (11)
13 (7)
18 (14)
44 (23)
19 (–)
49 (12)
12 (7)
18 (18)
40 (28)
18 (–)
39 (12 )
13 (6 )
17 (19 )
41 (30 )
20 (–)
31 (11)
12 (7)
18 (19)
39 (30)
21 (–)
21 (12)
12 (6)
18 (20)
35 (33)
23 (–)
19 (11)
13 (6)
18 (19)
35 (30)
a
Negligible extraction percentages are denoted with two consecutive hyphens (–). The error that represent the 95% confidence interval of the mean corresponding to
measurements of lanthanide concentration in solid–liquid extraction experiments was previously estimated to be lower than 19% – Ref. [31].
The extraction data also illustrate difficulty in interpretation of the
H
N
100
80
60
40
20
0
results, as polymers with crown motifs have good extraction per-
centages and selectivities in organic media, but polymers with
podand host motifs have better results in water. In this regard,
podands are likely not restricted to a fixed cavity size, as are
crowns, and conformational changes can adapt the shape and size
of the podand arms to the cation guest.
The rationalisation of the interaction of crown ether species
with cations, both in aqueous and organic media, is cumbersome
and cannot be easily carried out, as pointed out by Calderon
et al. [31]. In principle, the better the fit of the cation radii to the
crown ether cavity, the higher stability constant of the complex,
and the higher expected extraction percentage. On the other hand,
the polymethacrylates having pendant crown ethers have a comb-
like structure that could give rise, upon interaction with cations, to
sandwich structures with the participation of two or three vicinal
crown moieties (e.g., zip structures and pseudo-cryptands), modi-
fying the expected extraction selectivity due to the generation of
cavities of different sizes and shapes.
O
O
]
X
N
H
[
O
NH
O
O
3
O
O
O
O
X
O
13c
O
3
O
O
La(III) Ce(III) Pr(III) Nd(III) Sm(III) Eu(III) Gd(III) Tb(III)
Lanthanide ions
Fig. 10. Solid–liquid extraction of lanthanide ions in acetonitrile solution using
solid-phase polymers (13c and a polyamide with a benzo-18-crown-6 pendant
structure-data and error bars representing the 95% confidence interval of the mean
were taken from Ref. [31]).
4. Conclusion
with the difference in concentration being part of the driving force
of the process.
The synthesis and characterisation of methacrylic polymers
having pendant crown ethers or their dipodal, open chain counter-
parts is reported, along with the study of their polymerisation
kinetics and thermal properties in terms of structure–property
relationships. The potential applications of these materials have
been exemplified in the extraction of cations from aqueous and or-
ganic media using crosslinked polymers as solid phases in solid–li-
quid extraction experiments.
As previously mentioned, crown ethers are key structures in
supramolecular chemistry as species that have a cavity specially
suited for the complexation of cations whose cation radii fit well
into the diameter of this cavity. Nevertheless, in aqueous media
the strong solvation of charged species hinders the interaction of
an organic supramolecular entity in this environment. This fact is
more important in neutral host molecules, such as crown ethers.
Thus, as noted previously, the very low stability constants (Ks) of
crown ether polymers exist in aqueous solution for charged spe-
cies, such as lanthanide cations. For instance, the interaction of
Tb3+ and Eu3+ with a methacrylate with pendant aliphatic 12-
crown-4 moieties gave rise to a Ks = 22 and 1.9 Mꢁ1, respectively.
These interactions caused a loss of one to two water coordination
molecules, out of the possible 9. The interaction in the solid state
is much higher, as it also is in the gel state, as demonstrated using
water-swelled membranes that lost 5 water coordination mole-
cules for Tb3+ (a water-swelled, crosslinked membrane prepared
with a methacrylate with a pendant aliphatic residue of 15-
crown-5, indicating the replacement of a coordination molecule
of water for each oxygen of the crown moiety) [35,36]. In a similar
fashion, these interactions in organic solvents are much stronger
than in water.
Acknowledgments
We gratefully acknowledge financial support provided by the
Spanish Ministerio de Ciencia e Innovación – Feder (MAT2008-
00946) and by the Junta de Castilla y León (BU001A10-2).
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