L -arabinitol-based functional polyurethanes

Article abstract of DOI:10.1002/pola.24530

Three new polymerizable diols, based on mono-, di-, and tri-O-allyl-L-arabinitol derivatives, were prepared from L-arabinitol as versatile materials for the preparation of tailor-made polyurethanes with varied degrees of functionalization. Their allyl fun

Full text of DOI:10.1002/pola.24530

L-Arabinitol-Based Functional Polyurethanes
CRISTINA FERRIS, M. VIOLANTE DE PAZ, JUAN A. GALBIS
Dpto. Quı´mica Orga´nica y Farmace´utica, Facultad de Farmacia, Universidad de Sevilla, 41012 Sevilla, Spain
Received 26 November 2010; accepted 29 November 2010
DOI: 10.1002/pola.24530
Published online 3 January 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Three new polymerizable diols, based on mono-,
di-, and tri-O-allyl-L-arabinitol derivatives, were prepared from
L-arabinitol as versatile materials for the preparation of tailor-
made polyurethanes with varied degrees of functionalization.
Their allyl functional groups can take part in thiol-ene reac-
tions, to obtain greatly diverse materials. This ‘‘click’’ reaction
with 2-mercaptoethanol was firstly studied on the highly hin-
dered sugar precursor 2,3,4-tri-O-allyl-1,5-di-O-trityl-L-arabinitol,
coupling reaction took place in every allyl group, as confirmed
by standard techniques. The thermal stability of the novel poly-
urethanes was investigated by thermogravimetric analysis and
differential scanning calorimetry (DSC). This strategy provides
a simple and versatile platform for the design of new materials
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whose functionality can be easily modified. 2011 Wiley Peri-
odicals, Inc. J Polym Sci Part A: Polym Chem 49: 1147–1154,
2011
to apply it later to macromolecules.
A polyurethane with
multiple pendant allyl groups was synthesized by polyaddition
reaction of 2,3,4-tri-O-allyl-L-arabinitol with 1,6-hexamethylene
diisocyanate, and then functionalized by thiol-ene reaction. The
KEYWORDS: functionalization of polymers; differential scanning
calorimetry; polyurethanes; sugar-based monomers; thermog-
ravimetric analysis
INTRODUCTION The preparation and applications of polyur-
ethanes have been extensively studied for the last few deca-
des; these polymers have been mainly used as commodity
materials and/or in industrial applications.1 Similarly, the
use of polyurethanes in biomedicine is being widely investi-
gated due to their low toxicity, potential biodegradability,
biocompatibility, and versatile structures.2 Most of their
applications are as plasticizer-free thermoplastic elastomers
in the preparation of a wide range of medical devices,
including thin-walled flexible tubing, catheters, surgical
drains, intra-aortic balloon pumps, and so forth. Because of
their excellent biocompatibility and low thrombogenicity, bio-
degradable polyurethanes can be used as nonpermanent
devices.
ethylene glycol copolymer was also prepared as a drug car-
rier with tumor-targeting groups in its side chains.4 Simi-
larly, drug release systems based on poly(2-hydroxyethyl
methacrylate) and poly(2-hydroxypropyl methacrylate)
hydrogels were recently reported for use in ophthalmology.5
In addition, Harada et al. reported the synthesis of a polyeth-
ylene glycol and polyaspartic acid block-copolymer, which
can be used as drug carrier of the anticancer Docetaxel, co-
valently attached by ester bonds to the polymer chains.6
Poly(b-amino esters) with pendant hydroxyl groups were
proved to be good as gene delivery polymers as well.7
The modification of polymers after the successful achieve-
ment of a polymerization process is an important task in
macromolecular science. Click chemistry (CC) may serve as a
powerful strategy in its search. CC has emerged as a wide-
spread approach that uses only the most-practical and -reli-
able chemical transformations, with an explosive growth in
publications in recent years.8–10 Although fitting the require-
ments of a click reaction is a tall order, several processes did
so. Thus, the thiol-ene coupling reaction is a well-established
click reaction that combines a thiol moiety and an alkene/
alkyne group in a robust, efficient, and orthogonal method
for the functionalization of different compounds.11 Allyl
groups can be used in thiol-ene coupling reactions as the
‘‘ene’’ part with great success.12–14 Although allyl groups
have been widely used as curing agents in polymer chemis-
try,15–17 examples of linear soluble thermoplastic polymers
with allyl pendant groups are scant.18–20
The rational design of polymers tailored to exert distinct bio-
logical functions plays an important role in the development
of controlled drug delivery systems. Thus, the controlled
release of therapeutic molecules of both hydrophilic and
hydrophobic drugs is achieved by anchoring the active agent
to polymer structures by means of physical interactions or
by covalent linkages.
Various hydroxyl-containing polymers have been synthesized
for biomedical applications: for example, the anchorage of
hemoglobin to a derivatized poly(ethylene glycol-co-lactic
acid-co-polycaprolactone) was achieved by hydrogen-bond
interactions with the amine, hydroxyl, and carboxylic acid
moieties present in the polymer structure;3 a carbonate-poly-
Correspondence to: J. A. Galbis (E-mail: jgalbis@us.es)
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 1147–1154 (2011) 2011 Wiley Periodicals, Inc.
L-ARABINITOL-BASED FUNCTIONAL POLYURETHANES, FERRIS, DE PAZ, AND GALBIS
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
The aim of this work was the synthesis of mono-, di-, and
tri-O-allyl-L-arabinitol-based diol monomers useful for the
preparation of well-established and systematically varied
multifunctional polyurethanes with allyl pendant groups for
later derivatization via CC. We have applied this method to
the synthesis of a tri-O-allyl-L-arabinitol-based polyurethane
which was later derivatized with 2-mercaptoethanol to get a
highly hydroxylated material.
Synthesis of Monomers
2,3,4-Tri-O-allyl-1,5-di-O-trityl-L-arabinitol (3)
To sodium hydride (60% w/w) (1.24 g, 31.1 mmol) washed
with dry pentane (40 mL ꢁ 3) under argon atmosphere, a
solution of the ditrityl compound 2 (6.00 g, 9.43 mmol) in
drꢀy tetrahydrofuran (THF) (50 mL) wasꢀadded dropwise at
0 C. The mixture was then stirred at 30 C for 1 h, allyl bro-
mide (2.7 mL, 31.1 mmol) was added, and the reaction pro-
ceeded overnight. Methanol (5 mL) was added dropwise,
and the mixture was stirred for 1 h. The reaction mixture
was evaporated to dryness, and the residue was dissolved in
a 1:1 mixture of CH2Cl2 and H2O (200 mL). The organic
phase was washed with water (50 mL), dried (anhydrous
MgSO4), and evaporated to dryness. The residue was purified
by column chromatography (1:9 tert-butylmethyl ether-hex-
ane) to give the title compound as a white solid (5.10 g,
72%). M.p. (methanol) 65–66 ꢀC. [a]D þ9.5ꢀ (c 1.0, CHCl3).
IR: m (cmꢂ1) 3058, 3022 (CAH arom.), 1645 (C¼¼C), 1071
EXPERIMENTAL
Common reagents and solvents were purchased from Aldrich
Chemical Co. and used as received. Solvents were dried
and purified, when necessary, by appropriate standard
procedures.
Optical rotations were measured in a Perkin-Elmer 341 po-
larimeter 20 6 0.5 ꢀC (1 dm cell). Elemental analyses were
determined in the Microanalysis Laboratories of the CITIUS
Service, in the University of Seville. IR spectra were recorded
on a JASCO FT/IR-410 spectrometer. NMR spectra were
recorded at 300 K on either a Bruker Advance AV-500 or a
Bruker AMX-500 spectrometer. Chemical shifts (d) are
reported as parts per million downfield from Me4Si. Mass
spectra were obtained using a Kratos MS80RFA instrument.
Gel permeation chromatography (GPC) analyses were per-
formed using a Waters apparatus equipped with a Waters
1
(CAOAC). H NMR (CDCl3, 500 MHz): d (ppm) 3.12 (dd, 1H,
H-5a, JH-5a,H-4 ¼ 4.4 Hz, JH-5a,H-5b ¼10.2 Hz), 3.23 (dd, 1H, H-
1a, JH-1a,H-2 ¼ 6.7 Hz, JH-1a,H-1b ¼9.5 Hz), 3.40 (dd, 1H, H-1b,
JH-1b,H-2 ¼5.4 Hz, J ¼ 9.5 Hz), 3.48 (dd, 1H, H-5b, JH-5b,H-4
¼
2.4 Hz, J ¼ 10.2 Hz), 3.65 (ddd, 1H, H-4, J ¼ 2.4 Hz, J ¼ 4.4
Hz, JH-3,H-4 ¼ 7.8 Hz), 3.76–3.80 (m, 2H, 2CH2CH¼¼), 3.82–
3.85 (m, 1H, H-2), 3.92 (dd, 1H, H-3, JH-2,H-3 ¼3.1 Hz, J ¼ 7.8
Hz), 3.95–4.01; 4.12–4.16; 4.23–4.27 (m, 4H, 2CH2CH¼¼),
4.81–4.86; 5.10–5.12; 5.20–5.23; 5.33–5.36 (m, 6H, 3CH2¼),
5.37–5.45; 5.85–5.92; 5.98–6.06 (m, 3H, 3CH¼¼), 7.23–7.51
(m, 30H, Ph). 13C NMR (CDCl3, 125 MHz): d (ppm) 62.3 (C-
5), 62.7 (C-1), 71.4, 72.3, 73.6 (3C, 3CH2CH¼¼), 77.6 (C-3),
77.9 (C-2/C-4), 86.4, 86.9 (2C, CPh3), 116.4, 116.6 (3C,
CH2¼), 126.8, 127.0, 127.7, 127.8, 128.7, 128.8, 144.0, 144.1
(Ph), 135.0, 135.1, 135.3 (3C, CH¼¼).
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2414 refractive-index detector and two Styragel HR col-
umns (7.8 ꢁ 300 mm2) linked in series, thermostatted at 60
ꢀC, using N-methylpyrrolidone as the mobile phase, at a flow
rate of 0.5 mL minꢂ1. Molecular weights were estimated
against polystyrene standards. The thermal behavior of the
polyurethanes was examined by differential scanning calo-
rimetry (DSC), using a Perkin-Elmer DSC-7 calorimeter cali-
brated with indium. DSC data were obtained froꢂm1 samples
of 4–6 mg at heating/cooling rates of 10 ꢀC min under a
nitrogen flow. The glass transition temꢂp1eratures were deter-
mined at a heating rate of 20 ꢀC min from rapidly melt-
quenched polymer samples. Thermogravimetric analyses
were performed under nitrogen atmosphere (flow rate 100
mL minꢂ1) with a Universal V4.3A TA instrument at a heat-
HRFABMS: Calculated molecular weight for C52H52O5Na (M
þ Na)þ 779.3705; experimental molecular weight: 779.3712.
Anal. Calcd. for (C52H52O5): C, 82.51, H, 6.92. Found: C,
82.55, H, 7.14.
3,4-Di-O-allyl-1,5-di-O-trityl-L-arabinitol (5)
This was obtained from 1,5-ditrityl-L-arabinitol 2 following
the procedure described previously for 3 at 20 ꢀC. The
amounts used were the following: compound 2 (3.80 g, 5.97
mmol), sodium hydride (60% w/w) (0.48 g, 20.1 mmol) and
allyl bromide (1.0 mL, 11.9 mmol) in THF (30 mL). The reac-
tion was worked up as mentioned above, and the residue
was purified by column chromatography (1:5 tert-butyl-
methyl ether-hexane) to give the title compound as a white
soliꢀd (2.6 g, 60% yield). M.p. (1:1, diethyl ether-hexane) 60–
61 C. [a]D þ 11.0ꢀ (c 1.0, CHCl3). IR m (cmꢂ1) 3286 (OAH),
3057, 3022 (CAH arom.), 1646 (C¼¼C), 1069 (CAOAC). 1H
ꢂ1
ꢀ
ing rate of 10 C min
.
The polymerization reactions were performed in absence of
humidity, under inert atmosphere. All glassware was heated
overnight at 80 ꢀC before use, and after assembly was fur-
ther heated under vacuum to eliminate the surface moisture.
The diol monomer 2,3,4-tri-O-allyl-L-arabinitol (ArAll3, 4)
was dried under high vacuum for at least 3 days. 1,6-Hexam-
ethylene diisocyanate (HMDI) was stored at 4 ꢀC, and the
diol monomer at room temperature—both were handled
under inert atmosphere. N,N-Dimethylformamide (DMF) was
used as polymerization solvent and was further dried to
eliminate residual water. DMF was vacuum distilled and
stored over molecular sieve in a desiccator for not more
than a week before use. The other reactants and reagents for
the polymerizations were stored in a desiccator under inert
atmosphere until required.
NMR (CDCl3, 500 MHz): d (ppm) 3.01 (d, 1H, OH, JOH,H-2
6.2 Hz), 3.23 (dd, 1H, H-5a, JH-5a,H-4 ¼ 6.5 Hz, JH-5a,H-5b ¼ 9.4
Hz), 3.30–3.35 (m, 2H, H-1), 3.39 (dd, 1H, H-5b, JH-5b,H-4
5.6 Hz, J ¼ 9.4 Hz), 3.78–3.83 (m, 4H, H-3/H-4/1CH2CH¼¼),
3.99–4.04 (m, 1H, H-2), 3.87–3.91; 4.08–4.11 (m, 2H,
1CH2CH¼¼), 4.96–5.00; 5.11–5.22 (m, 4H, 2CH2¼), 5.51–5.59;
5.79–5.87 (m, 2H, 2CH¼¼), 7.23–7.53 (m, 30H, Ph). 13C NMR
¼
¼
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ARTICLE
(CDCl3, 125 MHz): d (ppm) 62.4 (C-5), 64.5 (C-1), 70.2 (C-
2), 72.1, 72.6 (2C, CH2CH¼¼), 77.5 (C-3), 77.7 (C-4), 86.8,
86.9 (2C, CPh3), 117.1, 117.6 (2C, CH2¼), 127.0, 127.1,
127.8, 127.9, 128.6, 128.7, 143.8, 143.9 (Ph), 134.8 (2C,
CH¼¼). MS (CI): m/z 739 (M þ Na)þ, 243 (Ph3C)þ, 91
(C7H7)þ.
CH¼¼), 7.24–7.51 (m, 30H, Ph). 13C NMR (CDCl3, 125 MHz): d
(ppm) 58.1 (CH3), 61.6, 62.4 (C-1/C-5), 72.4, 73.6 (2C,
CH2CH¼¼), 77.4, 77.6, 79.7 (C-2/C-3/C-4), 86.4, 86.9 (2C,
CPh3), 116.6, 116.8 (2C, CH2¼), 126.9, 127.0, 127.7, 127.8,
128.7, 128.8, 144.0, 144.1 (Ph), 134.9, 135.3 (2C, CH¼¼).
HRFABMS: Calculated molecular weight for C50H50O5Na (M
Anal. Calcd. for (C49H48O5): C, 82.09, H, 6.75. Found: C,
81.93, H, 6.52.
þ Na)þ 753.3572; experimental molecular weight: 753.3556.
4-O-Allyl-2,3-di-O-methyl-1,5-di-O-trityl-L-arabinitol (9)
This was obtained by methylation of compound 8 following
the procedure described previously for compound 6. The
amounts used were the following: allyl derivative 8 (0.80 g,
1.18 mmol), sodium hydride (60% w/w) (0.11 g, 2.60
mmol) and methyl iodide (0.15 mL, 2.38 mmol) in THF (20
mL). The reaction was worked up as mentioned above, and
the residue was purified by column chromatography (1:9
tert-butylmethyl ether-hexane) to give the title compoundꢀas
a white solid (1.75 g, 90% yield). M.p. (methanol) 58–59 C.
[a]D þ14.0ꢀ (c 1.0, CHCl3). IR: m (cmꢂ1) 3058, 3022 (CAH
arom.), 1596 (C¼¼C), 1073 (CAOAC). 1H NMR (CDCl3, 500
MHz): d (ppm) 3.08–3.10 (m, 4H, CH3/H-1a), 3.18 (dd, 1H,
H-5a, JH-5a,H-4 ¼ 7.4 Hz, JH-5a,H-5b ¼ 9.3 Hz), 3.41 (dd, 1H, H-
5b, JH-5b,H-4 ¼ 5.4 Hz, J ¼ 9.3 Hz), 3.43–3.45 (m, 1H, H-2),
3.46 (s, 3H, CH3), 3.49 (dd, 1H, H-1b, JH-1b,H-2 ¼ 2.2 Hz,
JH-1a,H-1b ¼ 10.2 Hz), 3.75 (dd, 1H, H-3, JH-3,H-4 ¼ 2.6 Hz,
JH-2,H-3 ¼ 8.2 Hz), 3.85 (ddd, 1H, H-4, J ¼ 2.6 Hz, J ¼ 5.4 Hz,
J ¼ 7.4 Hz), 3.96–4.00; 4.11–4.15 (m, 2H, CH2CH¼¼), 5.12–
5.25 (m, 2H, CH2¼), 5.85–5.93 (m, 1H, CH¼¼), 7.23–7.53 (m,
30H, Ph). 13C NMR (CDCl3, 125 MHz): d (ppm) 58.0, 60.7
(2C, CH3), 61.7 (C-1), 62.3 (C-5), 72.3 (CH2CH¼¼), 77.5 (C-4),
79.7 (C-3), 79.8 (C-2), 86.5, 86.9 (2C, CPh3), 116.7 (CH2¼),
126.9, 127.0, 127.7, 127.8, 128.7, 128.8, 144.1, 144.2 (Ph),
135.3 (2C, CH¼¼).
4-O-Allyl-1,5-di-O-trityl-L-arabinitol (8)
This was obtained from 1,5-ditrityl-L-arabinitol 2 following
the procedure described previously for 3 at 20 ꢀC. The
amounts used were the following: compound 2 (2.50 g, 3.93
mmol), sodium hydride (60% w/w) (0.17 g, 4.32 mmol) and
allyl bromide (0.34 mL, 3.97 mmol) in THF (20 mL). The
reaction was worked up as mentioned above, and the resi-
due was purified by column chromatography (1:5 tert-butyl-
methyl ether-hexane) to give the title compound as a white
solid (1.39 g, 52% yield). M.p. (1:1, diethyl ether-hexane)
70–71 ꢀC. [a]D þ4.0ꢀ (c 1.0, CHCl3). IR: m (cmꢂ1) 3565
(OAH), 3057, 3022 (CAH arom.), 1596 (C¼¼C), 1068
(CAOAC). 1H NMR (CDCl3, 500 MHz): d (ppm) 2.46 (d, 1H,
OH, J ¼ 7.5 Hz), 2.62 (d, 1H, OH, J ¼ 6.1), 3.27–3.39 (m, 4H,
H-1/H-5), 3.69–3.81 (m, 3H, H-2/H-3/H-4), 3.90–3.94; 4.13–
4.17 (m, 2H, CH2CH¼¼), 5.11–5.20 (m, 2H, CH2¼), 5.80–5.87
(m, 1H, CH¼¼), 7.16–7.45 (m, 30H, Ph). 13C NMR (CDCl3, 125
MHz): d (ppm) 63.9, 64.9 (C-1/C-5), 71.0, 72.1, 76.7 (C-2/C-
3/C-4), 72.0 (CH2CH¼¼), 86.8, 87.1 (2C, CPh3), 117.2 (CH2¼),
127.0, 127.1, 127.8, 127.9, 128.6, 128.7, 143.8, 143.9 (Ph),
134.7 (CH¼¼). MS (CI): m/z 699 (M þ Na)þ, 243 (Ph3C)þ, 91
(C7H7)þ.
Anal. Calcd. for (C46H44O5): C, 81.63, H, 6.55. Found: C,
81.48, H, 6.58.
HRFABMS: Calculated molecular weight for C48H48O5Na (M
3,4-Di-O-allyl-2-O-methyl-1,5-di-O-trityl-L-arabinitol (6)
To sodium hydride (60% w/w) (0.07 g, 1.7 mmol) washed
with dry pentane (20 mL ꢁ 3) under argon atmosphere, a
solution of 5 (0.80 g,ꢀ 1.10 mmol) in dry THF (15 mL) was
added dropwise at 0 C. The mixture was then heated at 30
ꢀC for 1 h, methyl iodide (80 lL, 1.21 mmol) was added, and
stirring was continued overnight. Methanol (1 mL) was
added dropwise, and the suspension was stirred for 1 h. The
reaction mixture was evaporated to dryness, and the residue
was then dissolved in a 1:1 mixture of CH2Cl2 and H2O (80
mL). The organic phase was washed with water (10 mL),
dried (anhydrous MgSO4), and evaporated to dryness. The
residue was purified by column chromatography (1:14 tert-
butylmethyl ether-hexane) to give the title compound as a
white solid (0.75 g, 94%). M.p. (methanol) 58–59 ꢀC. [a]D
þ13.5ꢀ (c 1.0, CHCl3). IR: m (cmꢂ1) 3057, 3031 (CAH arom.),
1595 (C¼¼C), 1070 (CAOAC). 1H NMR (CDCl3, 500 MHz): d
(ppm) 3.10 (dd, 1H, H-5a, JH-5a,H-4 ¼3.8 Hz, JH-5a,H-5b ¼ 10.0
Hz), 3.18 (dd, 1H, H-1a, JH-1a,H-2 ¼ 7.0 Hz, JH-1a,H-1b ¼9.4 Hz),
3.40 (dd, 1H, H-1b, JH-1b,H-2 ¼5.2 Hz, J ¼ 9.4 Hz), 3.47 (s, 3H,
CH3), 3.47–3.53 (m, 2H, H-5b/H-4), 3.74–3.76 (m, 2H,
1CH2CH¼¼), 3.89–3.91 (m, 2H, H-2/H-3), 4.00–4.03; 4.14–
4.17 (m, 2H, 1CH2CH¼¼), 4.77–4.83 (m, 2H, CH2¼), 5.12-5.26
(m, 2H, CH2¼), 5.34–5.39 (m, 1H, CH¼¼), 5.88–5.93 (m, 1H,
þ Na)þ 727.3399; experimental molecular weight: 727.3378.
2,3,4-Tri-O-allyl-L-arabinitol (ArAll3, 4)
Silica gel (3 g), activated by perchloric acid,21 was added to
a solution of 3 (2.00 g, 2.64 mmol) in methanol (50 mL),
and the reaction mixture was stirred at 25 ꢀC for 5 h. Silica
was filtered off, and the resulting solution was concentrated
to dryness. The residue was purified by column chromatog-
raphy (1:5 tert-butylmethyl ether-hexane) to give the title
compound as a colorless oil (0.60 g, 84%). [a]D ꢂ1.0ꢀ (c 1.0,
CHCl3). IR: m (cmꢂ1) 3420 (OAH), 3078 (CAH vinyl), 1646
1
(C¼¼C), 1063 (CAOAC). H NMR (CDCl3, 500 MHz): d (ppm)
2.34 (dd, 1H, OH, J ¼ 5.6 Hz, J ¼ 7.2 Hz), 2.37 (dd, 1H, OH, J
¼ 4.9 Hz, J ¼ 7.4 Hz), 3.63–3.67 (m, 2H, H-2/H-4), 3.72 (dd,
1H, H-3, J ¼ 4.6 Hz, J ¼ 5.7 Hz), 3.76–3.89 (m, 4H, H-1/H-5),
4.08–4.26 (m, 6H, 3CH2CH¼¼), 5.20–5.24; 5.29–5.31; 5.33–
5.34 (m, 6H, 3CH2¼), 5.91–6.00 (m, 3H, 3CH¼¼). 13C NMR
(CDCl3, 125 MHz): d (ppm) 60.7, 61.5 (C-1/C-5), 71.0, 71.8,
73.5 (3C, CH2CH¼¼), 79.0, 79.1, 79.2 (C-2/C-3/C-4), 117.3,
117.4, 117.5 (3C, CH2¼), 134.2, 134.6, 134.8 (3C, CH¼¼). MS
(CI): m/z 273 (M þ 1)þ, 57 (OAll)þ.
Anal. Calcd. for (C14H24O5): C, 61.74, H, 8.88. Found: C,
61.58, H, 8.50.
L-ARABINITOL-BASED FUNCTIONAL POLYURETHANES, FERRIS, DE PAZ, AND GALBIS
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
3,4-di-O-allyl-2-O-methyl-L-arabinitol (ArAll2, 7)
in a desiccator (0.27 g, 91% yield). Mw 13000; Mn 8700; Mw/
Mn 1.5. IR: m (cmꢂ1) 3325 (N–H), 3078 (C–H vinyl), 1695
(C¼¼O urethane), 1529 (N–H, N–C¼¼O, urethane), 1245
(CAN). 1H NMR (CDCl3, 500 MHz): d (ppm) 1.33 (bs, 4H,
CH2-h), 1.49 (bs, 4H, CH2-g), 3.15 (bs, 4H, CH2-f), 3.57–3.83
(m, 3H, H-2/H-3/H-4), 3.96–4.52 (m, 10H, 3CH2CH¼¼/H-1/H-
5), 4.98 (bs, 2H, 2NH), 5.12–5.30 (m, 6H, 3CH2¼), 5.84–5.94
(m, 3H, 3CH¼¼). 13C NMR (CDCl3, 125 MHz): d (ppm) 26.3
(CH2-h), 29.8 (CH2-g), 40.9 (CH2-f), 62.6, 63.6 (C-1/C-5), 71.0,
72.4, 73.9 (3C, CH2CH¼¼) 76.2, 78.4 (C-2/C-3/C-4), 117.1,
117.2, 117.3 (3C, CH2¼), 134.5, 134.6, 134.9 (3C, CH¼¼),
156.2, 156.4 (C¼¼O). Anal. Calcd. for (C22H36N2O7): C, 59.28,
H, 8.24, N, 6.36. Found: C, 59.27, H, 8.16, N, 6.26.
This was obtained from 6 following the procedure described
above for 4. The amounts used were the following: ditrityl
derivative 6 (0.50 g, 0.68 mmol), and activated silica (0.75 g)
in methanol (10 mL). The reaction was worked up as men-
tioned above, and the residue was purified by column chro-
matography (2:1 dichloromethane-tert-butylmethyl ether) to
give the title compound as an oil (0.15 g, 90% yield). [a]D
ꢂ3.5ꢀ (c 1.0, CHCl3). IR: m (cmꢂ1) 3414 (OAH), 1645 (C¼¼C),
1073 (CAOAC). 1H NMR (CDCl3, 500 MHz): d (ppm) 2.41
(bs, 1H, OH), 2.46 (bs, 1H, OH), 3.41–3.48; 3.55–3.62 (m, 5H,
CH3/H-2/H-4), 3.64–3.68 (m, 1H, H-3), 3.69–3.87 (m, 4H, H-
1/H-5), 4.02–4.22 (m, 4H, 2CH2CH¼¼), 5.14–5.20; 5.24–5.31
(m, 4H, 2CH2¼), 5.87–5.97 (m, 2H, 2CH¼¼). 13C NMR (CDCl3,
125 MHz): d (ppm) 57.5 (CH3), 59.9, 61.5 (C-1/C-5), 71.9,
73.5 (2C, 2CH2CH¼¼), 78.6, 78.7, 80.9 (C-2/C-3/C-4), 117.4,
117.5 (2C, CH2¼), 134.6, 134.7 (2C, CH¼¼).
2,3,4-Tri-O-[3-(2-hydroxyethylthio)propyl]-1,5-
di-O-trityl-L-arabinitol (11)
2,3,4-Tri-O-allyl-1,5-di-O-trityl-L-arabinitol (3, 0.20 g, 0.26
mmol) was dissolved in DMF (2 mL). The solution was
degassed, and 2-mercaptoethanol (1.1 mL, 15.6 mmol) and
2,20-azobisisobutyronitrile (AIBN) as radical initiator (0.13 g;
0.78 mmol) were added under argon atmosphere. The solu-
HRFABMS: Calculated molecular weight for C12H22O5Na (M
þ Na)þ 269.1365; experimental molecular weight: 269.1362.
4-O-Allyl-2,3-di-O-methyl-L-arabinitol (ArAll1, 10)
ꢀ
tion was stirred at 80 C for 24 h. The reaction mixture was
This was obtained from 9 following the procedure described
previously for 4. The amounts used were the following: ditri-
tyl derivative 9 (0.50 g, 0.71 mmol), activated silica (0.75 g),
and methanol (15 mL). The reaction was worked up afore-
mentioned, and the residue was purified by column chroma-
tography (tert-butylmethyl ether) to give the title compound
as an oil (0.15 g, 96% yield). [a]D ꢂ0.5ꢀ (c 1.0, CHCl3). IR: m
(cmꢂ1) 3397 (OAH), 1646 (C¼¼C), 1075 (CAOAC). 1H NMR
(CDCl3, 500 MHz): d (ppm) 2.33 (t, 1H, OH, J ¼ 5.7 Hz), 2.39
(t, 1H, OH, J ¼ 5.2 Hz), 3.44–3.46; 3.51–3.54 (m, 2H, H-2/H-
3), 3.47 (s, 3H, CH3), 3.55 (s, 3H, CH3), 3.61–3.66 (m, 1H, H-
4), 3.73–3.93 (m, 4H, H-1/H-5), 4.12–4.16; 4.21–4.25 (m, 2H,
CH2CH¼¼), 5.21–5.22; 5.23–5.24; 5.30–5.31; 5.34–5.35 (m,
2H, CH2¼), 5.93–6.02 (m, 1H, CH¼¼). 13C NMR (CDCl3, 125
MHz): d (ppm) 57.5, 60.6 (2C, CH3), 59.8, 61.5 (C-1/C-5),
71.9 (CH2CH¼¼), 79.0 (C-4), 80.7, 81.2 (C-2/C-3), 117.4
(CH2¼), 134.8 (CH¼¼).
then poured into cold water (30 mL) and extracted with
dichloromethane (3 x 50 mL). Sodium chloride was occasion-
ally added—when needed—to break the emulsion. The com-
bined organic layers were dried (anhydrous sodium sulfate)
and evaporated to dryness to give a slightly colored residue.
Purification was achieved by column chromatography (1:2
tert-butylmethyl ether-hexane) to give the title compound as
an uncolored oil (0.23 g, 89 % yield). [a]D þ1.0ꢀ (c 1.0,
CHCl3). IR: m (cmꢂ1) 3395 (OAH), 3056 (CAC arom.), 1066
1
(CAOAC). H NMR (CDCl3, 500 MHz): d (ppm) 1.39–1.45 (m,
2H, 1CH2-d), 1.83 (m, 2H, 1CH2-d), 1.90–2.00 (m, 2H, 1CH2-
d), 2.17–2.20 (m, 2H, 1CH2-c), 2.38 (bs, 2H, 2OH), 2.43 (bs,
1H, OH), 2.55–2.62; 2.67–2.70 (m, 8H, 2CH2-b/2CH2-c), 2.76 (t,
2H, CH2-b, JCH2-b,CH2-a ¼ 6.0 Hz), 3.09 (dd, 1H, H-5a, JH5a-H-4
¼ 4.9 Hz, JH5a-H5b ¼ 10.2 Hz), 3.22–3.79 (m, 18H, 3CH2-a/
3CH2-e/H-1/H-2/H-3/H-4/H-5b), 7.24-7.51 (m, 30H, Ph). 13C
NMR (CDCl3, 125 MHz): d (ppm) 28.2, 28.6, 28.7 (3C, CH2-c),
30.3, 30.4, 30.5 (3C, CH2-d), 35.0, 35.2, 35.3 (3C, CH2-b), 60.4,
60.5, 60.6, 69.0, 69.5, 71.0 (6C, 3CH2-a/3CH2-e), 62.5, 62.6 (C-
1/C-5), 78.8, 78.7, 78.6 (C-2/C-3/C-4), 86.6, 87.0 (2C, Ph3C),
127.0, 127.1, 127.7, 127.8, 128.7, 128.8, 144.0, 144.1 (Ph).
HRFABMS: Calculated molecular weight for C10H20O5: (M)þ
221.1389; experimental molecular weight: 221.1386.
Polymerization and Thiol-Ene Coupling Reactions
Polyurethane PU(ArAll3-HMDI) (12)
The diol monomer ArAll3 (4) (0.18 g, 0.67 mmol) was
loaded in a round-bottom flask with an argon/vacuum inlet.
The system was treated with three cycles of vacuum-argon
before the addition, via cannula, of dried DMF (5 mL). The
mixture was stirred to homogenization, and the diisocyanate
(HMDI, 0.11 mL, 0.67 mmol) was added under argon atmos-
phere, followed by the catalyst (dibutyltin dilaurate, one
drop). The polymerization solution was stirred at 60 ꢀC for
5 h under argon atmosphere. Triethylene glycol (0.2 mL) was
added, the mixture was stirred for 30 min, and the solution
was added dropwise into cold diethyl ether (250 mL), where
the polymer PU(ArAll3-HMDI) precipitated. The polyurethane
was purified by redissolution in a small volume of chloroform
(2 mL) and reprecipitation in diethyl ether. The pure polymer
(white solid) was dried under vacuum for 2 days and stored
HRFABMS: Calculated molecular weight for C58H70O8NaS3 (M þ
Na)þ 1013.4131; experimental molecular weight: 1013.4118.
Polyurethane PU[Ar(S-OH)3-HMDI] (13)
This was obtained from PU(ArAll3-HMDI) (12) following the
procedure described previously for 11. The amounts used
were the following: PU(ArAll3-HMDI) (0.05 g, 0.11 mmol),
DMF (1 mL), and AIBN (0.11 g; 0.66 mmol). The reaction
was worked up by precipitation over diethyl ether to give
the title polyurethane as a slightly colored syrup (0.07 g,
91% yield). Mw 14900; Mn 8100; Mw/Mn 1.8. IR: m (cmꢂ1
)
3319 (OAH, NAH urethane), 1695 (C¼¼O urethane), 1536
(NAH, NAC¼¼O, urethane), 1253 (CAN). 1H NMR (DMSO-d6,
500 MHz): d (ppm) 1.25 (bs, 4H, CH2-h), 1.40 (bs, 4H, CH2-
g), 1.72 (bs, 6H, CH2-d) 2.56 (bs, 12H, CH2-b/CH2-c), 2.97
1150
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
monomers 4, 7, and 10, which may be useful in the prepara-
tion of great numbers of chemically diverse polyurethanes
by means of subsequent thiol-ene coupling reactions. The
synthesis of the diol monomer 2,3,4-tri-O-allyl-L-arabinitol
(4) was accomplished following the synthetic Scheme 1. 3,4-
Di-O-allyl-2-O-methyl-L-arabinitol (ArAll2, 7) and 4-O-allyl-
2,3-di-O-methyl-L-arabinitol (ArAll1, 10) were prepared
according to Scheme 2. The structures of synthesized com-
pounds and polymers have been elucidated on the basis of
FTIR spectra, MS data, as well as 1D- and 2D-NMR experi-
ments [(1)H, (13)C, COSY, NOESY, DEPT, and HSQC)].
For the preparation of ArAll3 (4), a general protection–
deprotection strategy was followed. Thus, primary hydroxyl
groups of L-arabinitol (1) were blocked as trityl derivatives
by reaction with trityl chloride in pyridine, at 25 ꢀC, to give
1,5-di-O-trityl-L-arabinitol (2).22 The per-allylation of com-
pound 2 was accomplished using sodium hydride and allyl
bromide in dry THF, to generate 2,3,4-tri-O-allyl-1,5-di-O-tri-
tyl-L-arabinitol 3. A good control of the reaction temperature
(30 ꢀC) was needed to achieve high yields. Significant
amounts of partially substituted compounds 3,4-di-O-allyl-
1,5-di-O-trityl-L-arabinitol (5) and 4-O-allyl-1,5-di-O-trityl-L-
arabinitol (8) were formed when the reaction proceeded at
20 ꢀC or below. Trityl groups were then removed in com-
pound 3 by means of acid-mediated lyses, to give the triallyl
diol ArAll3 (4) in good yields (84%).
SCHEME 1 Synthesis of 2,3,4-tri-O-allyl-L-arabinitol 4. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
(bs, 4H, CH2-f), 3.38–3.84 (m, 15H, H-2/H-3/H-4/CH2-a/CH2-
e), 3.84–4.00; 4.01–4.21; 4.22–4.41 (m, 4H, H-1/H-5), 4.74
(bs, 3H, 3OH), 7.10 (bs, 2H, NH). 13C NMR (DMSO-d6, 125
MHz): d (ppm) 28.7 (CH2-h), 31.1 (C-c/C-b), 32.3 (CH2-g),
33.0 (C-d) 43.1 (CH2-f), 63.6 (C-a/C-e), 65.9 (C-1/C-5), 71.9,
72.6, 73.4 (C-2/C-3/C-4), 157.2 (C¼¼O). Anal. Calcd. for
(C28H54N2S3O10): C, 49.83, H, 8.06, N, 4.15, S, 14.25. Found:
C, 50.02, H, 7.84, N, 4.07, S, 14.10.
In the preparation of tailor-made polyurethanes with varied
degrees of functionalization, the use of monoallyl, diallyl, or
triallyl diol monomers accurately controls the amount of re-
active pendant groups incorporated into the polymer back-
bone. Therefore, the synthesis of diallyl and monoallyl by-
products (5 and 8, respectively) in good yields was under-
taken next. After treatment of 2 with sodium hydride, the
reaction temperature was kept below 20 ꢀC to enhance the
RESULTS AND DISCUSSION
Synthesis and Characterization of Monomers
In this study, the commercially available L-arabinitol (1) was
the starting material for the synthesis of functional allyl diol
SCHEME 2 Synthesis of diallyl and monoallyl diol monomers (7 and 10). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
L-ARABINITOL-BASED FUNCTIONAL POLYURETHANES, FERRIS, DE PAZ, AND GALBIS
1151

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 1 1H NMRs of compound 11 (top spectrum) synthesized from compound 3 (bottom trace).
chemoselectivity of allyl bromide toward the free hydroxyl
groups; thus, first the hydroxyl group at carbon 4 was substi-
tuted (rendering the monoallyl compound 8), followed by the
hydroxyl group at carbon 3 (to give the diallyl product 5).
tial and temporal control of the click reaction resulted in
well-defined, highly uniform polymer structures.
So we have investigated the derivatization of a novel polyur-
ethane via thiol-ene chemistry. 2-Mercaptoethanol was the
thiol of choice in the present study because of its simple and
convenient chemical structure. The reaction was firstly stud-
ied on sugar precursors. Therefore, 2,3,4-tri-O-allyl-1,5-di-O-
trityl-L-arabinitol (3) was used to resemble the great steric
hindrance that can be expected in the polymer backbone. An
excess of 2-mercaptoethanol was used to ensure a complete
addition to every allyl group. The reaction was conducted in
DMF, and oxygen was removed via argon bubbling. The trial
was thermally initiated by AIBN, leading to compound 11 in
high yields. In spite of the significant steric hindrance
exerted by the two trityl groups in the tri-O-allyl derivative
(3), total functional group conversion was achieved. Figure 1
displays the reaction scheme and the 1H-NMR spectra of
both the starting material 3 and the final compound 11. Of
note in the upper spectrum is the complete disappearance of
signals from the vinyl protons (4.7–6.2 ppm) and the appear-
ance of the peaks corresponding to the AOH groups (3H,
2.43 ppm) and to the a, b, c, and d methylene groups present
in the final compound.
The diallyl functionalization of ditrityl 2 to give compound 5
was confirmed by complete NMR characterization using
COSY, HSQC, DEPT, and NOESY experiments, and its structure
was unequivocally resolved. Thus, compound 5 bears a free
hydroxyl group on carbon 2, and an allyl ether moiety on
each of carbons 3 and 4. Homonuclear 2D-COSY experiments
revealed that the unsubstituted AOH group (d, 1H, 3.01
ppm) was coupled with a signal at 3.99–4.04 ppm (m, 1H,
H-2), which in turn can be correlated with an Ha-Hb system
at 3.30–3.35 ppm (m, 2H, H-1a and H-1b). The assignation
of H-2 was carried out by NOESY experiments. As the planar,
zigzag arrangement must be the preponderant conformation
in solution for the carbohydrate skeleton of 5,23–25 the spa-
tial correlation of H-2 with H-3 confirms this assignation.
Free secondary hydroxyl groups in compounds 5 and 8
needed to be blocked to avoid crosslinking reactions in poly-
mer synthesis. Their protection as methyl ether gave com-
pounds 6 and 9 in excellent yields (>90%), followed by
acid-mediated detritylation to render the diol monomers 3,4-
di-O-allyl-2-O-methyl-L-arabinitol (ArAll2, 7) and 4-O-allyl-
2,3-di-O-methyl-L-arabinitol (ArAll1, 10).
As far as we are aware, this method has not previously been
used in polyurethane chemistry. Consequently, its develop-
ment may be a new approach to well-defined reactive poly-
urethanes useful for a variety of biomedical and nanotechno-
logical applications.
Thiol-ene Reaction
The thiol-ene reaction shows all the desirable features of a
click reaction, that is, it is highly efficient, simple to execute
with no side products, and proceeds rapidly to high yields.11
This reaction was implemented in various synthetic methods,
including surface and polymer modification; its unique spa-
Synthesis and Characterization of Polymers
The thiol-ene method was applied to the synthesis of a novel
linear polyurethane. This method can be used for the
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ARTICLE
The precursor polymer PU(ArAll3-HMDI) (12) was prepared
by reaction of 2,3,4-tri-O-allyl-L-arabinitol (ArAll3, 4) with
HMDI (Scheme 3). Theꢀ polymerization took place under ar-
gon atmosphere at 60 C in DMF for 5 h to ensure the total
consumption of diol monomer. The recovered multiallyl poly-
urethane 12 was isolated by precipitation in diethyl ether
with excellent yields (>90%), and subsequently subjected to
the click reaction, where the thiol used was 2-mercaptoetha-
nol. The reaction conditions were similar to those described
for the preparation of compound 11, and the reaction was
allowed to proceed for 24 h, with complete coupling of thiol
fragments to every allyl moiety, giving the novel poly-
hydroxylated polymer PU[(Ar(S-OH)3-HMDI] (13).
Both new polymers were fully characterized by FTIR, NMR,
and GPC, and their thermal properties were also studied.
Molecular weights, polydispersities, and thermal properties
of polyurethanes are shown in Table 1. Although the thiol-
ene reaction carried out on PU(ArAll3-HMDI) (12) did not
increase the average length of polymer chains, it was
expected to increase the hydrodynamic volume; hence,
PU[(Ar(S-OH)3-HMDI] 13 exhibited an augmented weight av-
erage molecular weight (Mw) and polydispersity (Mw/Mn)
calculated by GPC compared with polyurethane 12.
The thermal analysis of the new polyurethanes showed that
they were stable to thermal degradation up to 200 ꢀC (Fig.
2); the presence of {3-[(2-hydroxyethyl)thio]propyl} frag-
ments in 13 had a marked effect on the degradation profile
compared with allyloxy pendant groups in 12, that is, those
groups shifted the decomposition onset temperature from
280 to 239 ꢀC, with an associated 10% weight loss (T0d),
leading to materials of lower thermal resistance. Moreover,
the degradation profile of polyurethane 13 displays other
major differences with that of polymer 12: first, the main
degradation peak (275 ꢀC, 43% weight loss) comes out at
lower temperature than in polymer 12 (318, 78% weight
loss); second, the degradation step at 455 ꢀC—probably
associated with the allyloxy groups in polymer 12—was not
observed.
SCHEME 3 Polymerization reaction of compound 4 with HMDI
and subsequent thiol-ene coupling reaction with 2-mercapto-
ethanol. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com.]
preparation of polyurethanes with enhanced properties,
namely higher hydrophilicity, increased wettability, improved
biodegradation behavior, and the preparation of highly func-
tionalized polymers such as polyanionic and polycationic
materials, and so forth through the combination of different
thiols and multi-ene polymers.
Thermal transitions associated to melting were not observed
in the DSC studies of polymers 12 and 13. This behavior
reveals that the materials are mainly amoꢀrphous. Both poly-
ꢀ
mers showed low Tg values (16 C and 9 C, respectively) in
TABLE 1 Molecular Weights and Thermal Properties of Synthesized Polyurethanes
GPC DSC TGA
Mw/Mn
DW (%)f
a
a
b
c
d
e
Polymer
Mw
Tm
Tg
Td0
Td
PU(ArAll3-HMDI)
13,000
14,900
1.5
1.8
–
–
16
9
280
239
318/455
275/300
78/18
46/37
PU[Ar(S-OH)3-HMDI]
a
Determined by GPC analysis against polystyrene standards using NMP as mobile phase.
First heating (10 ꢀC/min).
b
c
d
e
f
Second heating (20 ꢀC/min) after quenching from melting to ꢂ40 ꢀC.
Onset of decomposition (ꢀC).
Decomposition temperatures (ꢀC) measured at the peaks of the derivative curves; major peaks in bold.
Weight loss at the end of the decomposition step.
L-ARABINITOL-BASED FUNCTIONAL POLYURETHANES, FERRIS, DE PAZ, AND GALBIS
1153

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
REFERENCES AND NOTES
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tives obtained from 1,5-di-O-trityl-L-arabinitol (2) confirmed
that first the hydroxyl group on C-4 was substituted [render-
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hydroxyl group on C-3 [to give 3,4-di-O-allyl-1,5-di-O-trityl-L-
arabinitol (5)] and, finally, by the hydroxyl group on C-2
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di-O-trityl-L-arabinitol (3) and 2-mercaptoethanol was firstly
used as testing assay, and conversion of every allyl group
was achieved. This method was later applied to the synthesis
of a novel linear polyhydroxylated polyurethane. The precur-
sor polymer PU(ArAll3-HMDI) (12) was subjected to the
click reaction with complete coupling of thiol fragments to
every allyl group. Both polyurethanes are amorphous and
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ꢀ
thermally stable up to 239 C.
This method may be a new approach to well-defined reactive
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We thank the MICINN (Ministerio de Ciencia e Innovacio´n,
Grant MAT2009-14053-C02-02) and the Junta de Andalucı´a
(Grant P07-FQM-02648) of Spain for financial support.
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