Synthesis and properties of bio-based polyurethanes bearing hydroxy groups derived from alditols

Article abstract of DOI:10.1002/pola.24510

Four kinds of bio-based polyurethanes bearing hydroxy groups in the pendants were synthesized by the polyaddition of D-mannitol- and D,L-erythritol-derived diols (1,2:5,6-di-O-isopropylidene-D-mannitol and 1,2-O-isopropylidene-D,L-erythritol) with hexamethylene diisocyanate and methyl (S)-2,6-diisocyanatohexanoate and the subsequent deprotection of the isopropylidene groups. They were hydrolyzed much more quickly than the corresponding protected polyurethanes at 50 °C and pH 7.0, although their hydrolytic degradation rate was lower than that of polyurethanes with saccharic and glucuronic lactone groups, which had been reported in our previous articles. The introduction of D-mannitol units to the polyether-polyurethanes containing poly(oxytetramethylene) glycol units also enhanced their hydrolyzibility.

Full text of DOI:10.1002/pola.24510

Synthesis and Properties of Bio-Based Polyurethanes Bearing Hydroxy
Groups Derived from Alditols
KAZUHIKO HASHIMOTO, NAOYA HASHIMOTO, TAKEHIKO KAMAYA, JUNYA YOSHIOKA, HARUKI OKAWA
Department of Applied Chemistry, Faculty of Engineering, Kogakuin University, Nakano-cho, Hachioji,
Tokyo 192-0015, Japan
Received 30 September 2010; accepted 20 November 2010
DOI: 10.1002/pola.24510
Published online 3 January 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Four kinds of bio-based polyurethanes bearing
hydroxy groups in the pendants were synthesized by the poly-
addition of D-mannitol- and D,L-erythritol-derived diols (1,2:5,6-
di-O-isopropylidene-D-mannitol and 1,2-O-isopropylidene-D,L-
erythritol) with hexamethylene diisocyanate and methyl (S)-2,6-
diisocyanatohexanoate and the subsequent deprotection of the
isopropylidene groups. They were hydrolyzed much more
quickly than the corresponding protected polyurethanes at 50
lower than that of polyurethanes with saccharic and glucuronic
lactone groups, which had been reported in our previous
articles. The introduction of D-mannitol units to the polyether-
polyurethanes containing poly(oxytetramethylene) glycol units
also enhanced their hydrolyzibility. VC 2011 Wiley Periodicals,
Inc. J Polym Sci Part A: Polym Chem 49: 976–985, 2011
KEYWORDS: bio-based polymers; biopolymers; degradation; hy-
ꢀ
C and pH 7.0, although their hydrolytic degradation rate was
drolysis; polyurethanes; renewable resources
INTRODUCTION Modern human life has been supported by
enormous amounts of polymeric materials, and most of them
have been synthesized from fossil resources such as coal and
petroleum, which has been one of the reasons for environ-
mental pollution. Now polymer syntheses from renewable
and biomass resources are essential from the viewpoint of
enhance the hydrolysis of the urethane bonds in main
chains.
In addition, other polyurethanes bearing not only lactone
rings but also hydroxy groups in the repeating units have
been prepared through the polyaddition of L-gulonic acid-
derived diols (4 and 5) with diisocyanates, and the subse-
quent introduction of hydrophilic hydroxy groups into the
repeating units, and their hydroxy groups were also found to
enhance the hydrolyzability of lactone rings and as a result
to do that of carbamate groups in the polyurethanes
1
–10
carbon neutral.
Thus, various naturally occurring com-
pounds have been frequently adopted as starting blocks
mainly for biodegradable and/or biomedical polymeric mate-
rials. For example, several kinds of polyurethanes have been
1
1–13
14–16
synthesized from saccharides by Kurita,
and other investigators.
Bachmann,
At first, we have taken an in-
terest in saccharic and uronic lactones as starting materials
2
8
1
7–21
(Scheme 2).
Therefore, we are interested in the syntheses and properties
of the polyurethanes containing hydroxy groups but no lac-
2
2–24
and tried to synthesize new polyamides from them.
Then, we have reported the syntheses of bio-based polyur-
ethanes from D-glucose-derived diols such as D-glucaro-
29
tone rings in the repeating units. In this work, two alditol-
derived diols (1,2:5,6-di-O-isopropylidene-D-mannitol (6) and
1,4:6,3-dilactone (1), methyl D-glucofuranosidurono-6,3-lac-
1,2-O-isopropylidene-D,L-erythritol (7), respectively) prepared
tone (2), and 1,4:3,6-dianhydro-D-glucitol (3) (as shown in
Scheme 1), and from another aldose derivative, for example,
D-mannaro-1,4:6,3-dilactone, and found that the polyur-
ethanes containing dilactone or lactone rings prepared from
through the selective protection of hydroxy groups were
applied to the macromolecular syntheses of new linear poly-
urethanes having pendant hydroxy groups (11 and 12) by
their polyaddition with diisocyanates (8) and the subsequent
deprotection as shown in Scheme 3. The effects of hydroxy
groups on the hydrolyzability of the polyurethanes were
determined and compared with those of polyurethanes bear-
ing lactone groups reported in the previous articles.
1
and 2 were hydrolyzed in a neutral phosphate buffer solu-
tion to the corresponding saccharide derivatives, diamines,
ꢀ
and carbon dioxide at 27 C, whereas the polyurethanes con-
taining no lactone ring prepared from 3 were scarcely hydro-
2
5–27
lyzed in a similar condition.
The ring opening of lactone
groups in a phosphate buffer solution is inferred to increase
the hydrophilicity of polyurethane chains, which may also
New copolyurethanes (13 and 14) containing D-mannitol
diol (6) and poly(oxytetramethylene) glycol (15) units were
Correspondence to: K. Hashimoto (E-mail: hashimot@cc.kogakuin.ac.jp)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 976–985 (2011) V
2011 Wiley Periodicals, Inc.
C
976
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ARTICLE
SCHEME 1
also prepared to estimate the effects of the D-mannitol unit
on their hydrolyzability.
1,2:5,6-Di-O-isopropylidene-D-mannitol (MA, 6)
According to the method described by G.J.F. Chittenden,
3
0
D-mannitol (100 g) was stirred vigorously in 1,2-dimethoxy-
ethane (260 mL) containing tin (II) dichloride (104 mg).
Then 2,2-dimethoxypropane (160 mL) was added to the sus-
pension, and the mixture was refluxed with continuous stir-
ring until it became a clear solution. The solution was cooled
down, and a few drops of pyridine were added to the solu-
tion. After the solution was concentrated under reduced
pressure, the resulting crude crystals were dissolved in hot
di-n-butyl ether to filtrate off the insoluble part, and recrys-
tallized to give colorless crystals of 1,2:5,6-di-O-isopropyli-
EXPERIMENTAL
Reagents
N,N-Dimethylformamide (DMF) and dimethyl sulfoxide
(
Me SO) were dried over calcium hydride and distilled under
2
reduced pressure. Hexamethylene diisocyanate (HDI, 8a) was
purchased from Tokyo Kasei Lit. (Japan) and methyl (S)-2,6-
diisocyanatohexanoate (LDI, 8b) prepared from L-lysine was
provided from Kyowa Hakko Kogyo. (Japan). They were puri-
fied by the distillation under reduced pressure just before
use. meso-Erythritol and poly(oxytetramethylene) glycol
dene-D-mannitol (MA, 6), which were dried after washed
ꢀ
with petroleum ether: yield, 55 g (38%); mp, 120-121
C
(
PTMG; M ¼ 650 and 2000, 16) were supplied from Mitsu-
n
30
ꢀ
25
(
Lit., 122 C); [a]
D
, þ100.0 deg.
H NMR [270 MHz, DMSO-d , d, ppm]: 4,74 (d, 1H x 2,
ꢁOH), 4.0, 3.95, and 3.85 (m, 1Hþ1Hþ1H x 2, ꢁCH
bishi-kagaku Foods and Mitsui Chemicals. (Japan), respec-
tively. D-Mannitol, dibutyltin dilaurate and other reagents
were used without purification.
1
6
- and
2
SCHEME 2
BIO-BASED POLYURETHANES BEARING HYDROXY GROUPS, HASHIMOTO ET AL.
977

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 3
ꢁ
CH- in five-membered rings), 3.4 (t, ꢁCH-OH), 1.3, 1.2 (s,
ampoule, and di-n-butyltin dilaurate (4.6 mg) was added to
1
3
3
Hþ3H x 2, ꢁCH ). C NMR [67.5 MHz, DMSO-d , d, ppm]:
the solution drop by drop with stirring at room temperature.
3
6
ꢀ
108 (quaternary carbon in isopropylidene groups), 78 (-CH-
Then the ampoule was kept in a bath controlled at 50 C for
in five-membered rings), 70 (-CH-OH), 66 (-CH - in five-
membered rings), 27 and 25 (-CH3).
24 h. After quenching with a small amount of methanol for
24 h, the reaction mixture was poured into 100–200 mL of
diethyl ether. The resulting powdery polymer was collected,
washed with deionized water repeatedly, and dried in vacuo.
Yield of polyurethane (MAH) (9a), 1.55 g (98%).
2
1,2-O-Isopropylidene-D,L-erythritol (ER, 7)
In a similar method as aforementioned in the case of 1,2:5,6-
di-O-isopropylidene-D-mannitol (6), 2,2-dimethoxypropane
Synthesis of Copolyurethanes from PTMG (15),
D-Mannitol Diol (6), and Diisocyanate (8)
(
(
120 mL) was added to a suspension of meso-erythritol
100 g) in 1,2-dimethoxyethane (240 mL) containing Tin(II)
Polyol (PTMG; Mn ¼ 650, 15) and D-mannitol-derived diol
dichloride (50 mg), and refluxed with stirring until it became
a clear solution. After termination with a few drops of pyri-
dine, the reaction mixture was concentrated, and the residue
was dissolved in ethyl acetate. After removal of the
unreacted erythritol, the filtrate was concentrated again, and
recrystallyzed from a mixed solvent of n-hexane with ethyl
acetate (7:3 vol) to obtain colorless crystals; yield, 30 g
(MA, 6) were dried with diphosphorus pentoxide in vacuo.
Then, in a dry box filled with dry nitrogen 15 (3.29 g) and
HDI (8a, 1.22 g) were strictly weighed and dissolved in DMF
in a glass tube, and di-n-butyltin dilaurate (9.2 mg) was
added to the solution at room temperature. After the am-
ꢀ
poule was sealed, it was kept at 80 C for 3 h. The ampoule
ꢀ ꢀ
31
was put in the dry box again, and 6 (0.57 g) in DMF solution
(
22%); mp, 71–72 C (Lit., 40-42 C).
was added into the ampoule. It was sealed again and kept at
1
H NMR [270 MHz, DMSO-d , d, ppm]: 4.8 (d, 1H, ꢁCH-OH),
ꢀ
6
5
0 C for 24 h. The polyaddition reaction was quenched with
4
.5 (d, 1H, ꢁCH -OH), 3.8-4.0 (m, 2Hþ1H, ꢁCH - and ꢁCH-
2
2
a small amount of methanol for 24 h, and the mixture was
poured into 100–200 mL of diethyl ether. The resulting poly-
mer was collected, washed with deionized water repeatedly,
and dried in vacuo. Yield of the polyether-polyurethane (13a,
in five-membered ring), 3.3-3.5 (m, 2Hþ1H, ꢁCH -OH and
2
1
3
ꢁ
CH-OH), 1.3 and 1.2 (s, 3Hþ3H, ꢁCH
3
). C NMR [67.5
MHz, DMSO-d , d, ppm]: 108 (quaternary carbon in isopropy-
6
lidene group), 76 (-CH- in five-membered ring), 72 (-CH-OH),
4.38 g (86%).
6
6 (-CH - in five-membered ring), 63 (-CH -OH), 27 and 25
2
2
Deprotection of Polyurethanes
(
-CH3).
Polyurethane (9a, 501 mg) prepared from 6 and 8a was
added into a mixture of trifluoroacetic acid (50 mL) with
deionized water (25 mL), and the mixture was stirred vigo-
Polyaddition of the Alditol-Derived Diols
6, 7)) with Diisocyanates (8)
The D-mannitol-derived diol (MA, 6) was dried with diphos-
phorus pentoxide in a vacuum line for a week before use. In
a dry box filled with dry nitrogen, equimolar amounts of 6
(
ꢀ
rously at 10 C for 60 min. Then the solvent was distilled
out under reduced pressure, and the residue was reprecipi-
tated in ethyl acetate. The powder was centrifugated and
dried in vacuo. Yield of the polyurethane containing hydroxy
groups (11a), 400 mg (99%).
(
0.96 g, 3.68 mmol) and 8a (HDI, 0.62 g, 3.68 mmol) were
strictly weighed and dissolved in 3.2 mL of DMF in a glass
978
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
a
TABLE 1 Polyaddition of Alditol-Derived Diols (6 and 7) with Diisocyanates
Diisocyanate
g (mmol)
DMF
(mL)
Temp.
Time
(h)
Polymer
Yield (%)
b
Mw
ꢀ
b
ꢂ 10ꢁ3
Diol g (mmol)
( C)
M
n
Mn
2.1
1.6
1.9
5.3
1.8
2.4
2.0
1.9
1.9
1.9
1.6
1.9
1.6
6
6
6
6
6
6
6
7
7
7
7
7
7
3.10 (11.8)
8a
8a
8a
8b
8b
8b
8b
8a
8a
8a
8b
8b
8b
1.98 (11.8)
3.8
3.2
3.2
3.2
3.1
3.2
2.4
4.5
4.5
4.5
4.5
4.5
4.5
50
50
70
25
50
50
70
50
50
70
50
50
70
12
24
3
9a
87
98
83
93
86
94
82
90
85
91
91
89
94
7.0
12
0.96 (3.68)
2.28 (8.70)
1.00 (3.82)
2.79 (10.6)
1.03 (3.92)
2.23 (8.51)
2.12 (13.1)
2.12 (13.1)
2.13 (13.1)
2.22 (13.7)
2.22 (13.7)
2.21 (13.6)
0.62 (3.68)
1.46 (8.70)
0.64 (3.82)
2.26 (10.6)
0.83 (3.92)
1.81 (8.51)
2.20 (13.1)
2.20 (13.1)
2.21 (13.1)
2.90 (13.7)
2.91 (13.7)
2.90 (13.6)
9a
9a
6.1
2.7
24
12
24
3
9b
9b
11
14
6.5
9b
9b
12
24
3
10a
10a
10a
10b
10b
10b
12
16
17
13
18
21
12
24
3
a
Mole ratio of diol to diisocyanate, 1.00; catalyst, di-n-butyltin dilaurate, 1 mol %/monomer.
By GPC in DMSO (standard, poly(ethylene glycol)).
b
Hydrolyzability of Polyurethanes (9, 10, 11 or 12)
in a Phosphate Buffer
The degradation point was defined as a temperature at
which 10 wt % of the polymer was reduced. The matrix
assisted laser desorption ionization-time of flight (MALDI-
TOF) mass spectrum of oligourethane was measured with a
Perceptive Biosystem model Voyager Elite ST(DE) mass spec-
trometer using a-CHCA as a matrix.
In each test tube, 30 mg of the water-insoluble poly-
urethanes (9, 10, or 12) was dissolved in DMF or THF,
coated on the inside surface of the bottom, and the solvent
was subsequently evaporated with a rotary evaporator under
reduced pressure. Then, 8 mL of a phosphate buffer (pH 7)
ꢀ
was added to the tube, which was kept at 50 C for a desig-
RESULTS AND DISCUSSION
nated time. After the buffer solution was separated, the
residual film was washed with deionized water and dried
in vacuo. The recovered buffer solution was condensed, and
the residue was dialyzed in deionized water with a cellulose
tube (molecular weight cut off, 3500) and lyophilized for
recovery of the corresponding water-soluble polymer.
Polyaddition of Alditol-Derived Diols (6 and 7)
with Diisocyanates (8)
Generally speaking, the polyaddition of diols with diisocya-
nates at higher temperature is preferable to give high molec-
ular weight molecular weight polyurethanes quantitatively,
because of its higher apparent rate, but some side reaction is
apt to increase due to high reactivity of diisocyanates. Poly-
addition of 1,2:5,6-di-O-isopropylidene-D-mannitol (MA, 6) or
1,2-O-isopropylidene-D,L-erythritol) (ER, 7) with hexamethy-
lene diisocyanate (HDI, 8a) or methyl (S)-2,6-diisocyanato-
Since the polyurethane having hydroxy groups (11) was
soluble in water, 50 mg of the polyurethane was added in 10
ꢀ
mL of a phosphate buffer (pH, 7.0) and kept at 50 C. At
constant time intervals, 1 mL of the solution was taken out,
condensed, and the residue was dried under reduced
pressure.
ꢀ
hexanoate (LDI, 8b) was tried at 25 C, and mainly at 50
ꢀ
and 70 C. After the termination with methanol, the corre-
sponding colorless powdery polymers (9a, 9b, 10a, and
10b), which were also abbreviated as polyurethanes MAH,
MAL, ERH, and ERL, respectively, based on their starting
materials, were almost quantitatively as shown in Table 1.
Measurements
H NMR, C NMR, and their two-dimensional spectra were
taken with a JEOL EX-270 Fourier transform high-resolution
nuclear magnetic resonance spectrometer. Tetramethylsilane
1
13
ꢀ
Even on the polyaddition at 25 C, the polymer yield in the
(
TMS) was used as an internal standard in DMSO-d . The av-
6
case of 9b was almost quantitative, but the average molecu-
erage molecular weight of the polyurethanes was estimated
with a TOSOH Model HLC-8120 high-performance liquid
chromatogram apparatus using DMSO or THF as an eluent at
ꢀ
lar weight was lower than those at 50 and 70 C, in contrast
with that in the cases of the polyaddition of saccharic lac-
2
5,26,28
tone diols with diisocyanates reported in our works.
The apparent rate on the polyaddition of mannitol diol (MA,
) with diisocyanates may be lower than that in the cases of
0
.1 mL/min or 0.3 mL/min, respectively (column, TOSOH
TSK-gel GMHXL, f7.8 ꢂ 600 mm or Super HM-M, f 6.0 ꢂ
00 mm). Poly(ethylene glycol)s and polystyrenes with dif-
6
3
saccharic lactones.
ferent molecular weight were provided as standards, respec-
tively. Thermal stability was recorded on a Rigaku Model
Table 1 shows also that the average molecular weight of the
erythritol-derived polyurethanes (10) was higher than that
of the mannitol-derived ones (9) obtained on the
ꢀ
TG8120 thermogravimetric analyzer from 30 to 600 C at 10
ꢀ
C/min of heating rate under an atmosphere of dry nitrogen.
BIO-BASED POLYURETHANES BEARING HYDROXY GROUPS, HASHIMOTO ET AL.
979

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Properties of Polyurethanes (9 and 10) Prepared from
Alditol-Derived Diols (6 and 7) with Diisocyanates (8)
The degradation temperature (Td10) defined as the tempera-
ture, at which 10 wt % of the polymers was reduced, was
determined and summarized also in Table 2. The values of
Td10s for the mannitol-derived polyurethanes (9) were
Polyurethanes
ꢀ
higher than 230 C, but lower than those for the erythritol-
9a
9b
10a
10b
derived ones (10), regardless of diisocyanates provided for
the polyaddition. At any rate the values of Td10 for the aldi-
tol-derived polyurethanes containing no lactone rings were
much higher than those for the saccharic dilactone-derived
a
Solubility
Water
I
I
I
I
Me
2
SO
S
I
S
S
S
I
S
S
S
S
S
S
I
S
S
s
I
2
5
polyurethanes reported in our articles.
DMF
Methanol
Ethanol
I
Conversion to the Hydroxy-Bearing
Polyurethanes (11 and 12)
Table 3 shows the results on the deprotection of polyur-
I
Acetone
I
S
S
I
s
S
I
Tetrahydrofuran
Ethyl acetate
Chloroform
Diethyl ether
n-Hexane
I
ethanes (9 and 10) in a mixed solvent of trifluoroacetic acid
ꢀ
I
and deionized water (2:1 v/v) at 10 an 4 C for 60 and
30 min, which gave new polyurethanes (11 and 12) con-
I
S
I
S
I
S
I
taining four and two hydroxy groups in each repeating units,
respectively.
I
I
I
I
I
1
Thermal property
The H NMR spectroscopic analysis of the recovered polymer
ꢀ
b
(11a) shows that signals due to the isopropylidene groups
in the original polymer (9a) disappeared completely
and newly appeared signals assignable to hydroxy protons
(Fig. 1).
Degradation temperature ( C)
234
244
256
253
a
ꢀ
g/100 mL; S, soluble at room temperature; s, soluble at 40 C; I,
1
insoluble.
b
Defined as the temperature at which 10 wt % of the polyurethane was
lost.
As shown in Table 4, the solubility of the polyurethanes
having hydroxy groups in the repeating units (11 and 12)
were generally lower than that of the corresponding original
polyurethanes (9 and 10) respectively, mainly in nonpolar
solvents. It is noteworthy that polyurethanes 11 with four
hydroxy groups in the repeating units were dissolved in
water, but polyurethanes 12 with two hydroxy groups in the
units were not.
corresponding conditions. The apparent polyaddition rate in
the former case should be higher than in the latter case. In
addition, some side reaction may also be inevitable at 70 C
in the latter case. Such results may be caused by the struc-
tural difference between the mannitol-derived monomer (6)
and the erythritol diol (7), that is, the former has two pieces
of bulky isopropylidene groups and secondary hydroxy
groups but the latter has a reactive primary hydroxy group
and only one piece of isopropylidene group.
ꢀ
Hydrolyzability of Alditol-Derived Polyurethanes
(9, 10, 11, 12)
Taking into account that the bio-based polyurethanes con-
taining saccharic dilactone or lactone rings prepared from 1
and 2 were hydrolyzed in a neutral buffer solution at 27
All resulting polymers (9 and 10) were soluble in DMSO, but in-
soluble in water, ethyl acetate, ethyl ether, and n-hexane at
room temperature (see Table 2). The mannitol-derived polymers
ꢀ
25,26
C
but the polyurethanes containing no lactone rings
(
9a) prepared from HDI (8a) were insoluble in DMF, methanol,
from 1,4:3,6-dianhydro-D-glucitol (3) were scarcely hydro-
2
6
ethanol, acetone, THF, and chloroform, although the erythritol-
derived polymers (10a) were soluble in them. On the other
hands the solubility of polymer 9b prepared from lysine diiso-
cyanate (8b) was apt to be higher than that from HDI (8a).
lyzed in a similar condition, the alditol-derived polyur-
ethanes (9, 10, 11, 12) obtained in this work were also pre-
sumed not to be hydrolyzed in a neutral condition at room
temperature. Therefore the hydrolytic test for the
a
TABLE 3 Deprotection of Polyurethanes (9 and 10) Prepared from Alditol-Derived Diols (6 and 7) and Diisocyanates (8)
Polyurethane
Recovered
Polymer Yield
(%)
CF
3
COOH/
O (mL)
Temp.
Time
(min)
M
n
ꢂ 10ꢁ
3
mg
H
2
( C)
ꢀ
M
n
ꢂ10ꢁ3 b
9
9
1
1
a
8.3
10.8
8.3
501
505
75
10
10
4
60
60
30
30
11a
99
99
5.9
10.5
7.3
b
75
150
150
11b
12a
12b
0a
0b
1010
1030
95
c
8.8
4
61
15.3
a
c
A mixture of trifluoroacetic acid with water (volume ratio 2:1).
By GPC in DMSO (standard, polyethyleneglycol).
Incompletely recovered.
b
980
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ARTICLE
TABLE 4 Properties of Hydroxy-Bearing Polyurethanes (11 and
1
2)
Polyurethanes
1
1a
11b
12a
12b
a
Solubility
Water
s
S
S
S
S
I
I
I
DMSO
DMF
S
S
S
I
S
S
S
I
S
S
S
I
Methanol
Ethanol
Acetone
I
I
I
I
Tetrahydrofuran
Ethyl acetate
Chloroform
Diethyl ether
n-Hexane
I
I
I
i
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Thermal property
ꢀ
b
Degradation temperature ( C)
212
225
231
217
a
ꢀ
g/100 mL; S, soluble at room temperature; s, soluble at 40 C; I,
1
1
insoluble.
FIGURE 1 H NMR spectra of polyurethanes prepared from
,2:5,6-di-O-isopropylidene-D-mannitol (MA, 6) and hexamethy-
lene diisocyanate (HDI, 8a). Upper, before deprotection (9a);
b
Defined as the temperature at which 10 wt % of the polyurethane was
lost.
1
Lower, after deprotection (11a) (5% DMSO-d
6
solution, TMS, 40
ꢀ
C, 270 MHz).
ethanes (11, 12) were hydrolyzed relatively easily in a simi-
lar condition as summarized in Figures 2 and 3.
polyurethanes (9, 10, 11, 12) in this work was attempted in
a phosphate buffer solution (pH, 7.0) at 50 C.
The hydroxy groups were found to enhance the hydrolytic
degradation of urethane groups not only in the polymeric
chains containing lactones groups but also in the chains con-
taining no lactone groups. Since the existence of hydroxy
groups in the polyurethane should increase the
ꢀ
Among them, the hydrolysis of the hydroxy-protected polyur-
ꢀ
ethanes (9, 10) were found to be hard even at 50 C for 30
days. On the other hand, the hydroxy-containing polyur-
FIGURE 2 GPC profiles of polyur-
ethanes(MAH and MAL) before
and after hydrolysis in a phos-
ꢀ
phate buffer (pH, 7.0) at 50
C
(
column, TSK-GEL Super HMM;
eluant, DMSO). Polyurethanes
MAH), polyurethane (9a) pre-
(
pared from MA (6) and HDI (8a)
and its deprotected one (11a) ;
polyurethanes(MAL),
polyur-
ethane (9b) prepared from 6 and
methyl (S)-2,6-diisocyanatohexa-
noate (LDI, 8b) and its depro-
tected one (11b).
BIO-BASED POLYURETHANES BEARING HYDROXY GROUPS, HASHIMOTO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢀ
FIGURE 3 GPC profiles of polyurethanes(ERH and ERL) before and after hydrolysis in a phosphate buffer (pH 7.0) at 50 C (column,
TSK-GEL Super HMM; eluant, DMSO). Polyurethanes(ERH), polyurethane (10a) prepared from 1,2-O-isopropylidene-D,L-erythritol
(
ER, 7) and HDI (8a) and its deprotected one (12a); polyurethanes(ERL), polyurethane (10b) prepared from 7 and LDI (8b) and its
deprotected one (12b)
hydrophilicity near the polymeric chains, water molecules
are also reasonable to attack to the urethane groups in the
polymeric chains, which may lead to hydrolysis of the ure-
thane bonds.
minated with an excess of methanol, which shows that the
oligourethanes prepared in the first step have had isocyanate
groups at both chain ends as expected. The spectrum is
inferred to reflect the novel distribution of the PTMG
sequence (prepolymer unit) in the copolymer, too.
Introduction of D-Mannitol Units to the Industrial
Polyurethanes Containing Poly(tetramethylene glycol)
To control the hydrolyzability of the industrial polyur-
ethanes, the present mannitol units were tried to introduce
to the polyether-polyurethanes containing poly(tetramethy-
lene glycol) units through the following two-step polyaddi-
tion as shown in Table 5. The polyaddition proceeded in a
homogeneous phase almost quantitatively.
Therefore the resulting poly(tetramethylene glycol)-based
copolyurethanes should contain the mannitol units randomly
along the polymeric chains, of which the polymeric struc-
tures are expressed as 13 in Scheme 4. Such copolyur-
ethanes also could be converted by the deprotection in a
mixture of trifluoroacetic acid with water to those having
hydroxy groups along the chains (14) quantitatively.
Figure 4 is the MALDI-TOF mass spectrum of the reaction
Finally the hydrolytic tests of the poly(tetramethylene gly-
product obtained from 15 and 8a (mole ratio, 1:2) and ter-
col)-based copolyurethanes (13 and 14) were attempted in a
a
TABLE 5 Polyaddition of PTMG (15) and D-Mannitol-derived Diol (6) with Diisocyanates
b
c
First Step
Second Step
Polymer Yield
g (%)
PTMG
Diisocyanate
Diol 6
Mol % of
e
Mw
Mn
1.8
d
d
e
ꢂ10ꢁ4
g (mmol)
g (mmol)
g (mmol)
6 in Diol
M
n
5
3
2
1
1
4
3
2
1
a
.54 (8.5)
.29 (5.1)
.44 (3.8)
0.1 (5.0)
.53 (2.4)
8a
8a
8a
8a
8a
8b
8b
8b
8b
1.60 (9.5)
0.25 (1.0)
0.57 (2.2)
0.99 (3.8)
1.32 (5.0)
1.44 (5.5)
0.20 (0.8)
0.60 (2,3)
1.00 (3.8)
1.38 (5.3)
10
30
50
50
70
10
30
50
70
d
13a
6.34 (86)
4.38 (86)
3.69 (79)
11.1 (85)
3.34 (78)
6.01 (95)
5.26 (95)
4.38 (86)
3.51 (79)
3.9
2.5
1.7
2.5
0.6
3.1
1.7
1.2
0.9
1.22 (7.3)
1.27 (7.6)
1.68 (10))
1.32 (7.9))
1.63 (7.7)
1.61 (7.6)
1.62 (7.6)
1.60 (7.6)
13a
13a
13a
13a
13b
13b
13b
13b
1.8
1.9
2.0
1.9
1.7
1.9
1.8
1.7
f
.4 7 (6.9)
.45 (5.3)
.47 (3.8)
.47 (2.3)
Mole ratio of diol to diisocyanate, 1.00; catalyst, di-n-butyltin dilaurate,
M
n
, 650.
Estimated by GPC in THF (standard, polystyrene).
n
M , 2000.
e
f
1
mol %/monomer.
b
ꢀ
ꢀ
At 80 C for 3 h.
c
At 50 C for 24 h.
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WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 4 MALDI-TOF mass spectrum of oligourethane prepared by the polyaddition of PTMG (13; M
n
, 650) with HDI (6a) (mole
ratio, 1:2) and the subsequent termination with methanol.
ꢀ
phosphate buffer (pH, 7.0) at 50 C for 30 days. Since the
hydroxy-protected copolyurethanes (13) were recovered almost
without any changes of their weight and average molecular
weight, the changes of the hydroxy-containing copolyurethanes
(14) during the immersion in a phosphate buffer (pH, 7.0) were
determined in detail and summarized in Figures 5 and 6.
SCHEME 4
BIO-BASED POLYURETHANES BEARING HYDROXY GROUPS, HASHIMOTO ET AL.
983

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 5 Changes in the weight and average molecular weight of the water-insoluble polymers recovered after the immersion of
polyurethanes (14a), which were prepared by the polyaddition of PTMG (15) and MA (6) with HDI (8a) and the subsequent depro-
ꢀ
tection, in a phosphate buffer (pH, 7.0) at 50 C.
As expected, the weight of the recovered water-insoluble
copolyurethanes (14) and their average molecular weight
were found to reduce with the immersion time, although
their rates were lower than those of the corresponding
hydroxy-bearing polyurethanes having no poly(tetramethy-
lene glycol) unit (11). In other words, the hydrolytic degra-
dation of the urethane bonds in the hydrophobic poly(tetra-
methylene glycol)-based polyurethanes can be elucidated to
enhance with the amount of the hydrophilic hydroxy groups.
The present results also indicated that the hydroxy groups
should enhance the hydrolysis of the polyurethanes contain-
ing no lactone groups.
From the comparison of the results in Figures 5 and 6, the
hydrolytic rate of the copolyurethanes (14b) obtained from
FIGURE 6 Changes in the weight and average molecular weight of the water-insoluble polymers recovered after the immersion of
polyurethanes (14b), which were prepared by the polyaddition of 15 and 6 with 8b and the subsequent deprotection, in a phos-
ꢀ
phate buffer (pH, 7.0) at 50 C. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
984
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
methyl (S)-2,6-diisocyanatohexanoate (8b) was higher than
that of the copolyurethanes (14a) obtained from HDI (8a).
The hydrophilic carboxy groups resulting from the hydrolysis
of methyl ester groups in the 8b-derived units are also indi-
cated to enhance the hydrolytic degradation of the neighbor-
ing urethane bonds.
11 Kurita, K.; Hirakawa, N.; Iwakura, Y. Makromol Chem 1979,
180, 855–858.
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2 Kurita, K.; Hirakawa, N.; Morinaga, H.; Iwakura, Y. Makromol
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81, 1861–1870.
Instead of the mannitol-derived diol (6), the erythritol–
derived diol (7) was also introduced into the poly(tetra-
methylene glycol)-based polyurethanes, and similar effects of
hydroxy groups were observed, but the effects were lower
than those of the mannitol-derived units in the correspond-
ing copolyurethanes.
1
4 Bachman, F.; Reimer, J.; Ruppenstein, M.; Thiem, J. Makro-
mol Chem Rapid Commun 1998, 19, 21–26.
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1
In summary, new polyurethanes (9 and 10) bearing four or
two hydroxy groups in the repeating units were obtained
almost quantitatively by the polyaddition of the alditol-
derived diols, 1,2:5,6-di-O-isopropylidene-D-mannitol (6) and
1
7 Hanada, T.; Li, Y. J.; Nakaya, T. Macro Chem Phys 2001,
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1,2-O-Isopropylidene-D,L-erythritol (7), with diisocyanates
(8a and 8b) and the following deprotection. The protection
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This work was supported by Grant-in-Aid for establishing the
High Technology Research Center in Private Universities and
Research Project for the Japanese Ministry of Education, Cul-
ture, Sports, Science, and Technology.
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