Sugar-based hydrophilic polyurethanes and polyureas

Article abstract of DOI:10.1002/pola.24621

Novel linear homogeneous polyurethanes and polyureas with enhanced hydrophilic character have been successfully prepared from sugar-based monomers having their hydroxyl groups free or partially protected. By the reaction of primary hydroxyl groups of xyli

Full text of DOI:10.1002/pola.24621

Sugar-Based Hydrophilic Polyurethanes and Polyureas
´
´
BELEN BEGINES, FRANCISCA ZAMORA, ISAAC ROFFE, MANUEL MANCERA, JUAN A. GALBIS
Dpto. Quı´mica Orga´nica y Farmace´utica, Facultad de Farmacia, Universidad de Sevilla, 41012-Sevilla, Spain
Received 12 January 2011; accepted 1 February 2011
DOI: 10.1002/pola.24621
Published online 1 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Novel linear homogeneous polyurethanes and poly-
ureas with enhanced hydrophilic character have been success-
fully prepared from sugar-based monomers having their
hydroxyl groups free or partially protected. By the reaction of
primary hydroxyl groups of xylitol with dimethyl hexamethy-
lene dicarbamate (HMDC) or di-tert-butyl-4,40-diphenyl methyl
dicarbamate (MDC), two new linear semicrystalline polyur-
ethanes [PU(X-HMDC) and PU(X-MDC)] have been prepared.
Likewise, by the reaction of xylitol with the analogous diisocya-
nates hexamethylene diisocyanate (HMDI) or 4,40-methylene-
bis(phenyl isocyanate) (MDI), similar polyurethanes [PU(X-HMDI)
and PU(X-MDI)] were obtained. However, these latter poly-
urethanes present some degree of crosslinking because of the
higher reactivity of the diisocyanate comonomers. Linear hydro-
philic polyureas having free hydroxyl groups joined to the main
chain have also been prepared by the reaction of the same diiso-
cyanates (HMDI and MDI) with 1,6-diamino-1,6-dideoxy-D-manni-
tol and 1,6-diamino-1,6-dideoxy-3:4-O-isopropylidene-D-mannitol.
As far as we are aware, this kind of polyhydroxylated polyurea
has not been previously described in the literature. The new poly-
mers were characterized by standard methods (elemental analy-
ses, gel permeation chromatography, IR, and NMR). The
polyurethanes were hydrolytically degradable under physiologi-
cal conditions, in contrast with less-hydrophilic linear polyur-
ethanes previously described. The thermal properties of the novel
polymers were investigated by thermogravimetric analysis and
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differential scanning calorimetry.
2011 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 49: 1953–1961, 2011
KEYWORDS: hydrophilic polymers; polyurethanes; polyureas;
sugar-based monomers; thermal properties
INTRODUCTION Polyurethanes and polyureas are widely
used in many different fields, such as engineering, construc-
tion, and textiles, and for various applications, such as insu-
lating materials, elastomers, adhesives, fibers, and so on.1
However, homogeneous polyurethanes obtained from alkane-
diols and diisocyanates are chemically stable polymers with
a remarkable resistance to hydrolytic degradation.2 The
incorporation of sugar units into traditional condensation
polymers such as polyamides, polyesters, and polyurethanes
is considered an interesting method for the preparation of
new biodegradable and biocompatible materials for use in
biomedical applications.3,4
urethanes.15,16 Garcon et al.17 reported the synthesis of poly-
urethanes by the reaction of diisocyanates with glucopyrano-
sides. Donnelly et al.18,19 carried out the synthesis of
copolyurethanes based on the mixtures of commercial poly
(THFdiol)s with glucose. Go´mez and Varela20 recently
described D-galactose-based [n]-polyurethanes with the
hydroxyl groups protected as acetals and the corresponding
deprotected products. In our research group, we have used
O-protected L-threitol, L-arabinitol, and xylitol as monomers
for the preparation of a series of linear [m,n]-type poly-
urethanes by polycondensation in solution with 1,6-hexam-
ethylene diisocyanate (HMDI) or 4,40-methylene-bis(phenyl
isocyanate) (MDI).21–23 Fully O-benzylated polyurethanes
showed high resistance to hydrolytic degradation, whereas
the polyurethanes obtained by removing the O-protecting
groups, having free hydroxyl side groups, degraded signifi-
Despite their potential as biomaterials,5,6 the antecedents on
sugar-derived polyurethanes and polyureas are not very
numerous. The pioneering works of Kurita et al. described a
series of polyurethanes7,8 and poly(urea urethane)s9 by the
reaction of disaccharides and aminosugars, without prior
protection of the hydroxyl groups, with alkyl and aryl diiso-
cyanates. Thiem and coworkers10–14 described a series of
sugar-based polyurethanes and polyureas from the 1:4,3:6-
dianhydrohexitols with D-gluco, L-ido, and D-manno con-
figurations. Lactones based on glucaric and galactaric acid
react with diisocyanates by polyaddition to give poly-
23
ꢀ
cantly in saline buffer at pH 10 and 37 C.
In this article, we investigate the preparation of new linear
polyurethanes from sugar-based monomers with the
hydroxyl groups free or partially protected as cyclic acetals,
to enhance the hydrophilic character and hydrolytic degrad-
ability of the resultant polymers. We report on the synthesis
and characterization of new aliphatic and aromatic xylitol-
Correspondence to: J. A. Galbis (E-mail: jgalbis@us.es)
This article is dedicated to Professor Rafael Suau, in memoriam.
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 1953–1961 (2011) 2011 Wiley Periodicals, Inc.
SUGAR-BASED POLYURETHANES AND POLYUREAS, BEGINES ET AL.
1953

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Intrinsic Viscosity and Molecular Weights of
based polyurethanes by polymerization in solution or in
bulk, using diisocyanates or dicarbamates as comonomers. In
this way, a series of polyurethanes was prepared by poly-
addition reaction of xylitol with HMDI or MDI, and by poly-
condensation reaction of xylitol with dimethyl hexamethy-
lene dicarbamate (HMDC) or di-tert-butyl-4,40-diphenyl
methyl dicarbamate (MDC). We also describe the preparation
of sugar-based polyureas by polyaddition reaction of 1,6-dia-
mino-1,6-dideoxy-D-mannitol and 1,6-diamino-1,6-dideoxy-
3,4-O-isopropylidene-D-mannitol with HMDI and MDI.
Polyurethanes and Polyureas
ga (dL/g)
Mw
Mw/Mn
b
b
PU
PU(X-HMDI)
PU(X-MDI)c
PU(X-MDI)d
PU(X-MDI)e
PU(X-MDI)f
0.14
0.34
0.17
0.32
0.38
0.17
0.13
0.56
0.58
0.15
0.24
0.28
0.32
15,100
39,900
22,300
40,300
55,000
12,600
2,100
2.5
5.2
2.9
4.7
7.2
1.7
1.1
2.1
2.1
1.2
1.8
1.2
2.2
PU(X-HMDC)
PU(X-MDC)
PU(PD-HMDI)20a
EXPERIMENTAL
25,700
27,200
2,000
General Methods
PU(PD-MDI)20a c
,
All chemicals were used as purchased from Aldrich Chemical.
Solvents were dried and purified, when necessary, by appro-
priate standard procedures. HMDI ꢀ was vacuum distilled
before use, and MDI was stored at 4 C. HMDC was prepared
as previously described.24 All three compounds were
handled under inert atmosphere. Optical rotations were
measured at 20 6 5 ꢀC in a Perkin-Elmer 341 polarimeter.
Elemental analyses were determined in the Microanalyses
Laboratories of the CITIUS Service of the University of Seville
and in the Instituto de Investigaciones Quı´micas (CSIC) of
Seville. FTIR spectra were obtained with a Jasco FT/IR 4200
spectrometer equipped with ATR. NMR spectra were
recorded at 300 K on either a Bruker Advance AV-500 or a
Bruker AMX-300. Chemical shifts (d) are reported as parts
per million downfield from Me4Si. Mass spectra were
obtained using a Kratos MS80RFA instrument. Gel permea-
tion chromatography (GPC) analyses were performed using a
Waters apparatus equipped with a Waters 2414 refractive
PUR(IspM-HMDI)
PUR(IspM-MDI)
PUR(M-HMDI)
PUR(M-MDI)
a
11,400
5,000
55100
Intrinsic viscosity in dL/g determined in dichloroacetic acid at 25 ꢀC.
b
Determined by GPC analysis against polystyrene standards using
NMP as mobile phase.
c
Experiment made between ꢂ60 and ꢂ20 ꢀC.
d
Experiment made at ꢂ50 ꢀC for 30 min.
e
Experiment made at ꢂ50 ꢀC for 60 min.
f
Experiment made at ꢂ50 ꢀC for 300 min.
(1 mL) was added, and the mixture was stirred for 30 min.
The reaction mixture was added dropwise into cold tert-
butyl methyl ether where the polymer precipitated. The poly-
urethane was purified by dissolving the polymer in the mini-
mum volume of methanol and reprecipitation in acetone or
dichloromethane. The pure polymers (white solids or foams)
were dried under vacuum for 3 days and stored in a
desiccator.
R
index detector and two StyragelV HR columns (7.8 ꢁ 300
mm2) linked in series, thermostatted at 60 ꢀC, and using 1-
methyl-2-pyrrolidinone (NMP) as the mobile phase at a flow
rate of 0.5 mL/min. Molecular weights were estimated
against polystyrene standards. Intrinsic viscosity was deter-
mined in dichloroacetic acid (DCA) with an AMVn Automated
Microviscosimeter of Anton Paar. The thermal behavior of
the polymers was examined by differential scanning calorim-
etry (DSC), carried out under a nitrogen atmosphere using a
TA Instruments DSC Q200 calibrated with indium. DSC data
were obtained from samples of 2–4 mg at heating/cooling
rates of 10 ꢀC under a nitrogen flow of 20 mL/min. Glass
transition temperatures (Tg) were determined at a heating
rate of 20 ꢀC/min from rapidly melt-quenched samples.
Thermogravimetric analyses (TGA) were performed under a
nitrogen atmosphere (flow rate 100 mL/min) with aꢀuniver-
sal TA Instruments SDT Q600 at a heating rate of 10 C/min.
The different degree of crosslinking of polyurethane PU
(X-MDI) was studied by carrying out polymerization at
different temperatures and reaction times (Table 1).
PU(X-HMDI)
It was prepared from xylitol (0.76 g, 5 mmol) in dry DMF
(15 mL), HMDI (0.83 mL, 5 mmol), and dibutyltin dilaurate
(2% w/w). The mixture was stirred at ꢂ20 ꢀC until the
ꢀ
external temperature was raised to 5 C, as described in the
general procedure. The title compound was obtained as
white foam (1.5 g, 93%).
IR: m (cmꢂ1) 3323 (NH), 1682 (C¼¼O, urethane), 1531 (NH
d);1H NMR (DMSO-d6, 500 MHz): d (ppm) 1.24 (bs, 4H, H-c),
1.38 (bs, 4H, H-b), 2.95 (m, 4H, H-a), 3.42 (m, 1H, H-3), 3.72
(m, 2H, H-2, H-4), 3.90–4.01 (m, 4H, H-1a, H-5a, H-1b, H-5b),
4.29–5.01 (m, 3 OH), 7.05 (bs, 2H, NH); 13C NMR (DMSO-d6,
125 MHz): d (ppm) 26.0 (C-c), 29.4 (C-b), 40.0 (C-a), 65.7
(C-1, C-5), 69.6 (C-3), 70,9 (C-2, C-4), 156.4, 156.7 (C¼¼O).
Anal. calcd for (C13H24N2O7)n: C, 48.74; H, 7.55; N, 8.74.
Found: C, 48.74; H, 7.59; N, 8.73.
Polyurethane Synthesis from Diisocyanates
Xylitol was charged in a round-bottomed flask saturated
with inert gas. The chosen dried-distilled solvent was added,
and the mixture was stirred to homogenization and cooled
to temperatures of between ꢂ60 and ꢂ20 ꢀC. To this solu-
tion, diisocyanate (HMDI or MDI) and dibutyltin dilaurate
(2% w/w) were added as catalyst. The mixture was stirred
under inert atmosphere until the external temperature
PU(X-MDI)
It was prepared from xylitol (0.76 g, 5 mmol) in dry DMF
(10 mL), MDI (1.25 g, 5 mmol), and dibutyltin dilaurate (2%
ꢀ
ꢀ
raised to ꢂ20 C (MDI) or 5 C (HMDI). Finally, tert-butanol
1954
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
w/w). The mixture was stirred at ꢂ60 ꢀC until the external
temperature reached ꢂ20 ꢀC, as described in the general
procedure. The title compound was obtained as white foam
(1.6 g, 80%).
PU(X-MDC)
It was prepared from xylitol (76 mg, 0.5 mmol) and MDC
(200 mg, 0.5 mmolꢀ) in dry DMF (1 mL). The reaction mixture
was heated to 100 C, and then dibutyltin dilaurate (2% w/w)
was added. The solution was stirred at the same temperature
for 6 h under argon atmosphere, and the resulting solution
was poured dropwise into tert-butyl methyl ether, where the
polymer precipitated as white solid (100 mg, 51%).
IR: m (cmꢂ1) 3296 (NH), 1698 (C¼¼O, urethane), 1526 (NH
d); 1H NMR (DMSO-d6 , 500 MHz): d (ppm) 3.44 (m, 1H, H-
3), 3.64 (m, 2H, H-2, H-4), 3.84 (m, 2H, PhACH2APh), 4.07
(m, 2H, H-1b, H-5b), 4.18 (m, 2H, H-1a, H-5a), 4.30–5.00 (m,
3 OH), 7.08–7.33 (m, 8H, Ph), 9.50 (m, 2H, NH); 13C NMR
(DMSO-d6, 125 MHz): d (ppm) 40.3 (PhACH2APh), 66.6 (C-
1, C-5), 70.7, 72.4 (C-2, C-3, C-4), 118.8, 129.2, 129.3, 129.4,
129.6 (Ph), 137.5, 137.6, 137.7, 137.8, 137.9, 138.1 (Ph
C4io), 154.1, 154.2, 154.4 (C¼¼O). Anal. calcd for
[(C5H10O5)1.0(C15H12N2O2)1.2]n: C, 61.00; H, 5.43; N, 7.42.
Found: C, 61.27; H, 5.61; N, 7.76.
IR: m (cmꢂ1) 3297 (NH), 1697 (C¼¼O urethane), 1509 (NH
d); 1H NMR (DMSO-d6, 500 MHz): d (ppm) 3.30–3.57 (m,
3H, H-2, H-3, H-4), 3.78 (m, 2H, PhACH2APh), 4.02 (m, 3
OH), 4.4 (m, 4H, H-1a, H-1b, H-5a, H-5b), 7.20 (m, 8H, Ph),
8.50 (bs, 1H, NH), 9.17 (bs, 1H, NH); 13C NMR (DMSO-d6,
125 MHz): d (ppm) 39.6 (PhACH2APh), 62.7 (C-1, C-2),
70.1, 72.5 (C-2, C-3, C-4), 118.3, 128.7, 128.8, 128.9 (Ph),
134.9, 135.2, 137.4, 137.6 (Ph C4io), 152.5, 152.8 (C¼¼O).
Anal. calcd for (C20H22N2O7)n: C, 59.69; H, 5.51; N, 6.96.
Found: C, 59.58; H, 5.74; N, 6.94.
Polyurethane Synthesis from Diurethanes
MDC Diurethane
A mixture of 4,40-methylendianiline (1.6 g, 8 mmol) in aceto-
nitrile (10 mL), di-tert-butyldicarbonate (Boc)2O (4.62 mL,
20 mmol), and triethylamine (2.78 mL, 20 mmol) was stirred
at room temperature for 1 h. The resulting white solid was
purified by washing with tert-butyl methyl ether (2,6 g,
Hydrolytic Degradation Assays of Polyurethanes
Four polymer disks (160 6 10 lm thick) were made from
each polymer studied for each assay. The disks were pre-
pared by the application of 10 ton/cm2 pressure on pow-
dered (20 6 5 mg) for 5 min at 25 ꢀC. Samples were incu-
bated in buffer phosphate pH 7.02; the vials were sealed,
and heated at 37 6 0.5 ꢀC or 70 6 0.5 ꢀC for an exact
period of time. Once the soak times had finished, the result-
ing samples were filtered, and washed with double-distilled
water. The filtrate and the wash water were vacuum concen-
trated at room temperature. Finally, the residue obtained in
the evaporation of the filtrates and the retrieved disks were
dried at high vacuum and room temperature for several
days. The monitoring of the degradation was done by weigh-
ing the residual polymer disks and the residues resulting
from the evaporation of the mother liquor and by GPC stud-
ies, which determined the changes in the Mn, Mw, and poly-
dispersity values depending on the incubation times.
ꢀ
81%). M.p. 300 C (desc.).
1
IR: m (cmꢂ1) 3321 (NH), 1694 (C¼¼O), 1526 (NH d); H NMR
(DMSO-d6, 300 MHz): d (ppm) 1.46 [s, 18H, C(CH3)], 3.78
(bs, 2H, PhACH2APh), 7.20 (m, 8H, Ph), 8.52 (bs, NH), 9.21
(bs, NH); 13C NMR (DMSO-d6, 75 MHz): d (ppm) 28.1
[C(CH3)], 39.8 (PhACH2APh), 78.8 [C(CH3)], 118.3, 128.7,
128.8 (Ph), 134.9, 135.1, 137.6 (Ph C4io), 152.5, 152,7
(C¼¼O). HRMS (CI) (m/z): calcd for C23H30N2O4: 398.2206;
found: 398.2198.
PU(X-HMDC)
A mixture of xylitol (0.15 g, 1 mmol) and HMDC24 (0.29 g, 1
mmol) was introduced into a two-necked round-bottomed
flask equipped with a magnetic stirrer, an argon inlet, and a
vacuum distillation outlet. The flask was purged with argon
to remove all traces of moisture and residual air. The mix-
ture was heated to 100 ꢀC, and tetrabutyl titanate catalyst
(TBT; 1–2 mol %) was added. The reaction mixture was
stirred vigorously under argon flow at 170 ꢀC for 5 h and
then for a further period of 2 h at the same temperature
under vacuum (0.5–1 mmHg). The resulting colored solid
mass was dissolved in acetic acid, and the polymer was pre-
cipitated with hexane, collected by filtration, and thoroughly
washed with the same solvent. The solid polyurethane was
dried under vacuum (0.25 g, 80%).
Polyurea Synthesis
In a typical procedure, 1,6-diamino-1,6-dideoxy-3:4-O-isopro-
pylidene-D-mannitol25 or 1,6-diamino-D-mannitol26 was
charged in a round-bottomed flask saturated with inert gas;
dimethyl sulfoxide (DMSO) or N,N-dimethyl acetamide
(DMAc) was added while stirring, and the mixture was
stirred to homogenization at room temperature. The diiso-
cyanate HMDI or MDI was added, and the mixture was
stirred for 1 h at room temperature under inert atmosphere.
Finally, methyl amine was added, and the mixture was
stirred for 30 min. The reaction mixture was added drop-
wise into cold tert-butyl methyl ether to precipitate the poly-
mer. Purification of the polyurea was carried out by dissolv-
ing the polymer in the minimum volume of methanol or
dichloromethane and precipitation into tert-butyl methyl
ether. The pure polymers (white solids) were dried under
vacuum and stored in a desiccator until needed.
IR: m (cmꢂ1) 3335 (NH), 1685 (C¼¼O, urethane), 1526 (NH
1
d); H NMR (DMSO-d6, 500 MHz): d (ppm) 1.19 (m, 4H, H-c),
1.33 (m, 4H, H-b), 2.91 (m, 4H, H-a), 3.33 (m, 1H, H-3), 3.42
(m, 2H, H-2, H-4), 3.45–3.54 (m, 4H, H-1a, H-5a, H-1b, H-5b),
4.50 (bs, 3 OH), 7.05 (bs ,2H, NH); 13C NMR (DMSO-d6, 125
MHz): d (ppm) 26.9 (C-c), 29.8 (C-b), 40.3 (C-a), 63.2 (C-1,
C-5), 70.6 (C-3), 73.0 (C-2, C-4), 157.1 (C¼¼O). Anal. calcd for
[(C13H24N2O7)1.0(H2O)1.5]n: C, 44.95; H, 7.83; N, 8.06. Found:
C, 45.11; H, 7.77; N, 7.71.
PUR(IsopM-HMDI)
It was prepared from 1,6-diamino-1,6-dideoxy-3:4-O-isopro-
pylidene-D-mannitol25 (55 mg, 0.25 mmol) in DMAc (0.3
SUGAR-BASED POLYURETHANES AND POLYUREAS, BEGINES ET AL.
1955

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of polyurethanes.
mL) and HMDI (40 lL, 0.25 mmol), as described in the
general procedure. The title compound was obtained as
white solid. Yield (quant.); [a]D þ9 (c, 0.5, DCA).
NMR (DMSO-d6, 125 MHz): d (ppm) 26.0 (C-c), 29.9 (C-b),
39.1 (C-a), 43.3 (C-1, C-6), 69.6 (C-3, C-4), 70.0 (C-2, C-5),
158.6, 159.1 (C¼¼O). Anal. calcd for (C14H28N4O6)n: C, 48.26;
H, 8.10; N, 16.08. Found: C, 48.22; H, 8.23; N, 16.11.
IR: m (cmꢂ1) 3325 (NH, OH), 1618 (C¼¼O), 1569 (NH d,
urea); 1H NMR (DMSO-d6, 300 MHz): d (ppm) 1.23 (bs, 4H,
H-c), 1.30 (s, 6H, CH3), 1.31 (bs, 4H, H-b), 2.94 (m, 4H, H-a),
2.82–3.79 (m, 8H, H-1a, H-1b, H-6a, H-6b, H-2, H-3, H-4, H-
5), 5.77 (m, 2H, OH), 7.86 (bs, 4H, NH); 13C NMR (DMSO-d6,
75 MHz): d (ppm) 26.1 (C-c), 27.3 [C(CH3)2], 30.0 (C-b),
39.1 (C-a), 42.9 (C-1, C-6), 71.3 (C-3, C-4), 79.8 (C-2, C-5),
108.3 [C(CH3)2], 157.8, 158.4 (C¼¼O). Anal. calcd for
(C17H32N4O6)n: C, 52.56; H, 8.30; N, 14.42. Found: C, 52.51;
H, 8.08; N, 14.56.
PUR(M-MDI)
It was prepared from 1,6-diamino-1,6-dideoxy-D-mannitol26
(40 mg, 0.22 mmol) in DMSO (1 mL) and MDI (56 mg, 0.22
mmol), as described in the general procedure. The title com-
pound was obtained as white solid. Yield (quant.); [a]D ꢂ4
(c, 0.5, DCA).
IR: m (cmꢂ1) 3312 (NH, OH), 1646 (C¼¼O), 1595 (NH d,
urea); 1H NMR (DMSO-d6, 500 MHz): d (ppm) 3.04 (m, 4H,
H-1a, H-1b, H-6a, H-6b), 3.47 (m, 4H, H-2, H-3, H-4, H-5),
3.72 (s, 2H, PhACH2APh), 4.27 (d, 2H, J ¼ 8.2 Hz, OH), 4.84
(d, 2H, J ¼ 8.2 Hz, OH), 6.08 (bs, 2H, NHACH2), 7.01 (d, 4H,
J ¼ 8.1 Hz, Ph), 7.25 (d, 4H, J ¼ 8.1 Hz, Ph), 8.59 (bs, 2H,
NHAPh); 13C NMR (DMSO-d6, 125 MHz): d (ppm) 40.4
(PhACH2APh), 43.2 (C-1, C-6), 69.6 (C-3, C-4), 70.2 (C-2, C-
5), 117.7, 117.9, 118.3, 128.8 (Ph), 134.2, 135.5 (Ph C4io),
155.8 (C¼¼O). Anal. calcd for (C21H26N4O6)n: C, 58.59; H,
6.09; N, 13.02. Found: C, 58.59; H, 6.30; N, 13.24.
PUR(IsopM-MDI)
It was prepared from 1,6-diamino-1,6-dideoxy-3:4-O-iso-
propylidene-D-mannitol25 (55 mg, 0.25 mmol) in DMAc
(0.5 mL) and MDI (62.5 mg, 0.25 mmol), as described in the
general procedure. The title compound was obtained as
white solid. Yield (quant.); [a]D þ9 (c, 0.5, DCA).
IR: m (cmꢂ1) 3310 (NH, OH), 1647 (C¼¼O), 1596 (NH d,
urea); 1H NMR (DMSO-d6, 500 MHz): d (ppm) 1.32 (s, 6H,
CH3), 2.87 (m, 4H, H-1a, H-1b, H-6a, H-6b), 3.31 (m, 2H, OH),
3.77 (m, 2H, H-2, H-5), 3.78 (bs, 2H, PhACH2APh), 3.93 (m,
2H, H-3, H-4), 6.25 (bs, 2H, NHACH2), 7.12 (d, 4H, J ¼ 8.1
Hz, Ph), 7.28 (d, 4H, J ¼ 8.1 Hz, Ph), 8.85 (bs, 2H, NHAPh);
RESULTS AND DISCUSSION
Synthesis and Characterization of Polyurethanes
13C NMR (DMSO-d6, 125 MHz):
d (ppm) 27.3 (CH3),
Polyurethanes were firstly prepared by polyaddition reaction
of xylitol with HMDI or MDI, in DMF solution, at low temper-
atures, using dibutyltin dilaurate as catalyst (Scheme 1). The
reaction proceeded in one step, and isolation and purifica-
tion of the polymers were carried out by solution-precipita-
tion cycles and subsequent drying under vacuum. High yields
were attained (80–93%), with the samples appearing as
white foams or solids. Some characteristics of the obtained
polymers are collected in Table 1. The polymerizations were
carried out at low temperatures in order that the diisocya-
nates reacted only with the primary hydroxyl groups of the
xylitol, avoiding crosslinking reactions. In spite of this, a cer-
tain degree of crosslinking was observed in the obtained
polymers [PU(X-HMDI) and PU(X-MDI)], as inferred from the
analysis of the 1H and 13C NMR spectra and the results of
the elemental analyses. With the aim of preparing a batch of
samples of PU(X-MDI) having differing degrees of crosslink-
ing, polymerizations were carried out at ꢂ50 ꢀC and
39.7 (PhACH2APh), 42.6 (C-1, C-6), 68.8 (C-3, C-4), 79.5 (C-
2, C-5), 109.3 [C(CH3)2], 117.7, 118.2, 128.9 (Ph), 134.8,
137.8 (Ph C4io), 152.7 (C¼¼O). Anal. calcd for (C24H30N4O6)n:
C, 61.26; H, 6.43; N, 11.91. Found: C, 61.23; H, 6.11; N,
11.63.
PUR(M-HMDI)
It was prepared from 1,6-diamino-1,6-dideoxy-D-mannitol26
(45 mg, 0.25 mmol) in DMSO (0.5 mL) and HMDI (40 lL,
0.25 mmol), as described in the general procedure. The title
compound was obtained as white solid. Yield (quant.). [a]D
ꢂ13 (c, 0.5, DCA).
IR: m (cmꢂ1) 3315 (NH, OH), 1624 (C¼¼O), 1569 (NH d,
urea); 1H NMR (DMSO-d6, 500 MHz): d (ppm) 1.22 (bs, 4H,
H-c), 1.32 (bs, 4H, H-b), 2.80–3.05 (m, 4H, H-1a, H-1b, H-6a,
H-6b), 2.94 (m, 4H, H-a), 3.41 (m, 4H, H-2, H-3, H-4, H-5),
4.31 (m, 2H, OH), 4.84 (m, 2H, OH), 5.90 (m, 4H, NH); 13C
1956
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ARTICLE
TABLE 2 Thermal Properties of Polyurethanes and Polyureas
DSCa
TGAb
PU
Tg (ꢀC)
Tm (ꢀC)
DHm (J/g)
oTd (ꢀC)
maxTd (ꢀC)
DW (%)
PU(X-HMDI)
PU(X-MDI)c
PU(X-MDI)d
PU(X-MDI)e
PU(X-MDI)f
25
140
110
117
130
ꢂ8
211
241
238
241
233
214
230
310
288
222
262
236
242
236/332/449
247/299/349
271/310/348
259/298/355
265/355
53/34/6
40/20/21
45/27/12
55/19/13
71/22
PU(X-HMDC)
PU(X-MDC)
PU(PD-HMDI)21
PU(PD-MDI)21,23
PUR(IspM-HMDI)
PUR(IspM-MDI)
PUR(M-HMDI)
PUR(M-MDI)
a
112g
93
105
117
64
247/311/441
232/290/483
360/378/470
333/362
53/29/5
13/80/2
58/24/7
20h
ꢂ17
10
151
170
83
91
29
22
208
84
232/302/390
294/313
23/44/20
29/41
78
71
83
253/337
48/33
79
114
272/341
52/32
Glass transition temperature (Tg), melting temperature (Tm), and enthalpy (DHm) measured by DSC.
Onset decomposition temperature corresponding to 10% of weight loss (oTd), maximum rate decomposi-
b
tion temperatures (maxTd) and weight lost at the respective decomposition step [DW (%)] determined by
TGA.
c
Experiment made between ꢂ60 and ꢂ20 ꢀC.
d
Experiment made at ꢂ50 ꢀC for 30 min.
e
Experiment made at ꢂ50 ꢀC for 60 min.
f
Experiment made at ꢂ50 ꢀC for 300 min.
g
Second heating cycle.
h
Remaining weight after decomposition.
different reaction times. As expected, the degree of crosslink-
ing increased with reaction time (Table 1).
Because of the presence of the NH and OH groups in the
backbone of the polymer chain, these materials have a high
tendency to bond protic solvents. For this reason, despite
the long drying periods used, some samples contained a
residual amount of humidity.
These polyurethanes were also synthesized by polycondensa-
tion reactions from diurethane comonomers to minimize
crosslinking reactions, as the urethane group is less reactive
than the isocyanate group. The polyurethane PU(X-HMDC)
was prepared by the reaction of xylitol and HMDC by poly-
merization in bulk, using TBT (0.6 mmol per mol of mono-
mer) as catalyst. This reaction was carried out in two steps.
Polyurethane PU(X-MDC) was prepared from MDC and xylitol
in DMF solution and dibutyltin dilaurate (2% w/w) as cata-
lyst, because MDC melts at a temperature higher than
300 ꢀC, with decomposition. These polymers were obtained
in 80 and 51% yields, respectively. Some polymerization
data and polymer characteristics are collected in Table 1.
Nonhydroxylated polyurethanes PU(PD-HMDI)21 and PU(PD-
MDI)21,23 prepared from 1,5-pentanediol (PD) were used as
references (Tables 1 and 2).
The molecular weights were determined by GPC using NMP
as the mobile phase. The polyurethanes obtained from the
diurethanes presented lower values of Mw and polydisper-
sities than those obtained from diisocyanates but, apparently,
they did not undergo any crosslinking reactions.
Thermal Properties
The thermal stability of the PUs was evaluated by thermog-
ravimetry under inert atmosphere. Decomposition takes
place through a process of several stages, leading to final
residues of about 10% of the initial weight. Detailed temper-
ature and weight-loss data for all the studied compounds are
given in Table 2. The insertion of the sugar unit in the PU
chain produces a slight reduction in thermal stability when
compared with their unsubstituted homologs [PU(PD-HMDI)
and PU(PD-MDI)]; nevertheless, all the polymers remain
unaltered up to temperatures above 210 ꢀC and have maxi-
Chemical structures of the polyurethanes were validated by
FTIR and NMR spectroscopy; these data are fully detailed in
the experimental section. Characteristic IR absorption bands
of the urethane group and of the sugar moieties were
observed at the predicted positions and with their expected
intensities. 1H and 13C NMR spectra were in full agreement
with the expected chemical structures. The spectra recorded
from PU(X-HMDC), with the assignment of the signals, are
shown in Figures 1 and 2 for illustration.
ꢀ
mum decomposition rates at temperatures above 230 C. For
the aromatic polyurethanes (MDI derivatives), the onset of
decomposition is at higher temperatures than for the
aliphatic ones (HMDI derivatives), as observed previously in
other alditol-based polyurethanes.21
SUGAR-BASED POLYURETHANES AND POLYUREAS, BEGINES ET AL.
1957

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 1 1H NMR spectrum of
PU(X-HMDC).
Thermal transitions associated to melting were not observed
in the DSC studies of polymers PU(X-HMDI) and PU(X-MDI),
obtained from their respective diisocyanates. This behavior
reveals that the materials are mainly amorphous. The poly-
mers showed high Tg values (Table 2), especially the aro-
matic ones, obtained from MDI. However, the polyurethanes
obtained from the diurethanes PU(X-HMDC) and PU(X-MDC)
are semicrystalline materials of high crystallinity, showing
well-defined melting transitions with high melting enthalpies,
as is also shown by the reference nonhydroxylated poly-
urethanes derived from 1,5-pentanediol [PU(PD-HMDI)
and PU(PD-MDI)]. The different behavior of the two series of
polyurethanes confirms that those obtained from the diiso-
cyanates could present some degree of crosslinking, respon-
sible for their resistance to melting and for their higher Tg
values.
Hydrolytic Degradability
The hydrolytic degradation of these polyurethanes was eval-
uated and compared with that displayed by nonhydroxylated
polyurethanes such as the unsubstituted [PU(PD-HMDI)] and
other sugar-based polyurethanes with the hydroxyl groups
protected as benzyl-ethers.23 Polyurethanes PU(X-HMDI) and
PU(X-MDI) were incubated in parallel in aqueous buffer
FIGURE 2 13C NMR spectrum of
PU(X-HMDC). [Color figure can be
viewed in the online issue, which
is available at wileyonlinelibrary.
com.]
1958
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
TABLE 3 Hydrolytic Degradation Data of Polyurethanesa
PU(X-HMDI)b PU(X-MDI)b PU(X-MDI)c
Mw/Mn Mw Mw/Mn Mw Mw/Mn
tures. The molecular weights of the polymers were estimated
by GPC, which afforded weight-average values ranging
between 2000 and 55,000 and polydispersities between
1.2 and 2.2.
Time
(days) Mw
Thermal Properties
The DSC studies showed that the polyureas present a semi-
crystalline behavior. The thermograms were characterized by
0
15,100 2.5
39,900 5.2
30,400 4.0
28,800 4.0
24,300 4.0
17,600 3.6
39,900 5.2
39,000 5.2
26,900 5.0
19,500 3.8
9,400 3.2
3
3600 1.3
3500 1.3
2300 1.2
1900 1.3
10
20
40
a
ꢀ
a very wide endotherm centered at about 70–80 C and high
melting enthalpies. Only in the case of the PUR(IspM-HMDI)
could a Tg be detected in the second heating cycle. The ther-
mal stability of the PURs was evaluated by TGA studies.
All the polymers were stable up to temperatures of about
220 ꢀC, markedly higher than their melting temperatures
(Table 2).
In buffer solution at pH 7.02.
At 37 ꢀC.
b
c
At 70 ꢀC.
solution (pH 7.02) under different temperatures, and the
degradation was followed by sample weighing and GPC anal-
ysis. Under physiological conditions (pH 7.02 and 37 ꢀC),
PU(X-HMDI) disks presented a weight loss of between
50 and 65%. The retrieved disks remained undegraded,
whereas the soluble fraction underwent a 75% reduction in
Mw during the first 3 days of incubation. The degradation
was total at pH 7.02 and 70 ꢀC during the same period of
time. The PU(X-MDI) disks did not show any significant loss
of weight during incubation under the same conditions.
However, the remaining disks underwent a loss in Mw of 56
or 98% at pH 7.02 and 37 or 70 ꢀC, respectively (Table 3).
This behavior can be explained by the insolubility of the
degradation products in the incubation media. The degrada-
tion of both polyurethanes is characterized by a rapid
decrease in molecular weight during the first period of incu-
bation, followed by a second period in which degradation
proceeds at a lower rate (Fig. 3). The degradability exhibited
by these polyurethanes contrasts with that of the model non-
hydroxylated polyurethanes, in which no degradation was
perceived under the same conditions, and with the high
resistance to hydrodegradability displayed by O-benzylated
sugar-based polyurethanes23 and unsubstituted homogene-
ous polyurethanes.2
CONCLUSIONS
A batch of novel linear homogeneous polyurethanes and
polyureas with enhanced hydrophilic character has been suc-
cessfully prepared from sugar-based monomers having their
hydroxyl groups free or partially protected. By the reaction
of the primary hydroxyl groups of xylitol with HMDC
or MDC, two new linear semicrystalline polyurethanes
[PU(X-HMDC) and PU(X-MDC)] have been prepared. By the
reaction of xylitol with the analogous diisocyanates HMDI or
MDI, similar polyurethanes [PU(X-HMDI) and PU(X-MDI)]
were obtained. These new polymers were stiffer, showing
higher Tg values and no melting endotherm, probably due to
Synthesis and Characterization of Polyureas
Polyureas were prepared by reaction of 1,6-diamino-1,6-
dideoxy-3:4-O-isopropylidene-D-mannitol25 or 1,6-diamino-
1,6-dideoxy-D-mannitol26 with the diisocyanates HMDI and
MDI by polycondensation in DMSO or DMAc solution at
room temperature (Scheme 2). The reaction proceeded in
one step, and the polyureas were isolated and purified by
solution-precipitation cycles and subsequent drying under
vacuum. The yields obtained were quantitative, and the
products were obtained as white solids. Some polymerization
data and polymer characteristics are collected in Table 1.
The chemical structures of the polyureas were determined
by elemental analyses and FTIR and NMR spectroscopies;
these data are fully detailed in the experimental section.
Characteristic IR absorption bands of the urea groups and
the sugar moieties were observed at the predicted positions
and with the expected intensities. 1H and 13C NMR spectra
were in full concordance with the expected chemical struc-
FIGURE 3 Changes in Mw of the indicated polyurethanes ver-
sus incubation time under physiological conditions (pH 7.02
and 37 ꢀC). [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
SUGAR-BASED POLYURETHANES AND POLYUREAS, BEGINES ET AL.
1959

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 2 Synthesis of polyureas.
3 Galbis, J. A.; Garc´ıa-Mart´ın, M. G. In Monomers, Oligomers,
Polymers and Composites from Renewable Resources; Gandini,
A.; Belgacem, M. N., Eds.; Elsevier: Oxford, 2008; Chapter 5,
pp 89–114.
some degree of crosslinking because of the higher reactivity
of the diisocyanate comonomers.
Linear hydrophilic polyureas having free hydroxyl groups
joined to the main chain have also been prepared by the
reaction of the same diisocyanates (HMDI and MDI) with
1,6-diamino-1,6-dideoxy-D-mannitol and 1,6-diamino-1,6-
dideoxy-3:4-O-isopropylidene-D-mannitol. As far as we are
aware, this kind of polyurea has not previously been
described in the bibliography.
4 Galbis, J. A.; Garc´ıa-Mart´ın, M. G. In Carbohydrates in Sus-
tainable Development II; Rauter, A. P.; Queneau, Y.; Vogel, P.,
Eds.; Springer: Heidelberg, 2010; Vol. 295, Chapter 6, pp 147–
176.
5 Rattner, B. D. In Comprehensive Polymer Science; Allen, G.;
Bevington, J. Eds.; Pergamon Press: Oxford, 1989; Vol. 7.
All tꢀhese polymers are stable up to temperatures above
210 C, with maximum decomposition rates at temperatures
above 230 ꢀC. Some of them are semicrystalline materials
showing melting endotherms with high melting enthalpies.
Both polyurethanes are hydrolytically degradable under
physiological conditions, in contrast to other linear sugar-
based polyurethanes having O-protected hydroxyl groups
and to linear unsubstituted polyurethanes obtained from
alkanediols.
6 Tirrell, J. G.; Fournier, M. J.; Mason, T. L.; Tirrell, D. A. Chem
Eng News 1994, 72, 40–51.
7 Kurita, K.; Hirakawa, N.; Morinaga, H.; Iwakura, Y. Makromol
Chem 1979, 180, 2769–2773.
8 Kurita, K.; Hirakawa, N.; Iwakura, Y. Makromol Chem 1980, 181,
1861–1870.
9 Kurita, K.; Hirakawa, N.; Iwakura, Y. Makromol Chem 1977,
178, 2939–2941.
The authors thank the MICINN (Ministerio de Ciencia e Innova-
cio´n, Grant MAT2009-14053-C02-02) and the Junta de Andalu-
cı´a (Grant P07-FQM-02648) of Spain for financial support.
10 Thiem, J.; Lueders, H. Starch/Staerke 1984, 36, 170–176.
11 Thiem, J.; Lueders, H. Makromol Chem 1986, 187, 2775– 2785.
12 Bachmann, F.; Reimer, J.; Ruppenstein, M.; Thiem, J.
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SUGAR-BASED POLYURETHANES AND POLYUREAS, BEGINES ET AL.
1961