Macromolecules
Article
spectra were obtained with a Thermo Scientific Nicolet iS10 FTIR
spectrometer equipped with a Thermo Scientific Smart iTR with a
ZnSe crystal. IR spectra were recorded over a wavenumber range of
Scheme 1. Synthesis of BHF, PFS, and PFS/M2
−1
−1
6
00−3800 cm with 2 cm resolution. Intensities of absorption
peaks were calculated with the Fit Multiple Peak tool of OriginPro 8
software (OriginLab Corporation). Differential scanning calorimetry
(
DSC) was carried out on a Seiko EXSTAR6000 equipped with a
DSC6220N. Samples of 2−5 mg in an aluminum pan were analyzed
−1
from −40 to 150 °C or 200 °C at a heating rate of 10 °C min under
a N atmosphere. The mechanical properties of polymer samples were
2
evaluated using a Shimadzu EZ Test tensile testing machine at a cross-
−1
head speed of 5 mm min at room temperature. No. 2 (1/5)
dumbbell-shaped specimens described in JIS K 7113 (active region:
7
.0 mm × 1.4 mm × 0.3−0.4 mm) were used in tensile testing. Each
measurement was repeated at least four times, and the average values
were reported in order to ensure the reproducibility of data.
Synthesis of Bis(hydroxymethyl)furan (BHF). In a 200 mL
Schlenk flask, HMF (5 g, 40 mmol) was dissolved in dehydrated
tetrahydrofuran (15 mL) and kept at 0 °C in an ice bath. Sodium
borohydride (3 g, 79.3 mmol) was added to the flask slowly over 10
min, and then the reaction mixture was neutralized with HCl (2 N)
and extracted with ethyl acetate (3 × 40 mL). The organic phase was
dried with MgSO , and the product was recrystallized in a refrigerator
4
1
to afford a light yellow powder (4.4 g, 88.0%). H NMR (400 MHz,
DMSO-d , δ): 6.2 (s, 2H, furan), 5.1 (t, 2H, OH, J = 5.6 Hz), 4.3 (d,
6
4
H, CH , J = 5.6 Hz).
Synthesis of Poly(2,5-furandimethylene succinate) (PFS).
2
Under a N atmosphere, 20 mL of dehydrated dichloroethane was
2
added to a mixture of 1.5 g of BHF, 1.38 g of SA (11.7 mmol, 1 equiv),
and 4.28 g of N,N-dimethyl-4-aminopyridine (35.1 mmol, 3 equiv),
and then 4.43 g of N,N′-diisopropylcarbodiimide (35.1 mmol, 3 equiv)
was slowly added. The mixture was kept at room temperature for 1
day, the solvent was evaporated, and the product was purified by
maleimide groups (F/M ratio). When the F/M ratio is larger
than one, unreacted furan groups remain even after cross-
linking, promoting the healing process by increasing the
opportunity for bismaleimide to reconnect the failure surfaces.
Though polycondensation of 2,5-furandicarboxylic acid, an
oxidation product of HMF, with appropriate diols also gives
precipitation from chloroform with excess methanol to afford a yellow
1
solid (1.78 g, 85.2%). H NMR (400 MHz, CDCl , δ): 2.68 (4H,
3
12−14
analogous furan polyesters,
the electron-withdrawing effect
succinic acid−CH ), 5.05 (4H, BHF−CH ), 6.36 (2H, furan). DSC:
2
2
−
1
of the carbonyl groups directly connected to the furan ring
prevents the DA reaction with maleimide.
T
g
= 15 °C, T
m
= 79 °C, ΔH = 26 J g .
m
Cross-Linking of PFS with Bismaleimide (PFS/M ). Mixtures of
2
PFS and M (F/M molar ratio = 2/1, 3/1, 4/1, 6/1, 8/1, or 10/1)
In this study, we chose succinic acid (SA) as the
dicarboxylate for polyester synthesis. Like BHF, SA is a bio-
based compound: it can be produced from sugars by microbial
2
were prepared as films cast from chloroform solution. Each film was
compression-molded between two Teflon sheets with an aluminum
spacer (0.2 mm thickness) using a hot press (Imoto, Japan) at 130 °C
for 5 min under a pressure of 5 MPa. Each sample was quenched to 40
3
8,39
fermentation.
A homopolyester of BHF and SA was
synthesized (Scheme 1b) and cross-linked by a bismaleimide
°
C, held at this temperature for 3 h, and then held at room
temperature for at least 24 h.
linker, M (Scheme 1c). The F/M ratio was varied from 2/1 to
2
1
0/1. The mechanical properties of the resulting cross-linked
Healing Tests. In each self-healing experiment, a dumbbell
polymers were studied along with their self-healing ability and
their ability to be healed by the application of M solution or
specimen was first torn by the tensile test machine with a cross-
−1
head speed of 5 mm min . The two broken surfaces were then
immediately reunited, subjected to gentle pressure, and stored
horizontally at room temperature for 1−10 days without any
2
pure solvent. In order to make bio-based polymers more
competitive with petroleum-based chemicals, development of
bio-based polymers with high performance would be an
effective way. The bio-based furan polymer reported herein
may broaden the potential applications of both bio-based and
self-healing materials.
continued pressure. To test healing promoted by M solutions, the
2
broken surfaces made by the tensile testing machine were immersed in
−1
M solution (0−100 mg mL in chloroform) for about 1 s and were
2
then immediately reunited and kept at room temperature for 1−10
days without any continued pressure.
EXPERIMENTAL SECTION
■
1
RESULTS AND DISCUSSION
■
Materials. 5-(Hydroxymethyl)furfural (HMF), succinic acid (SA),
N,N-dimethyl-4-aminopyridine, N,N′-diisopropylcarbodiimide, and
Preparation of PFS/M . Two PFSs with degrees of
2
3
3
,1-dichloroethane were purchased from Tokyo Chemical Industry.
polymerization, n, of 24 (M = 5.1 × 10 , M = 8.1 × 10 )
n w
3 3
Sodium borohydride was purchased from Aldrich. 1,8-Bis(maleimido)-
and 27 (M = 5.7 × 10 , M = 9.3 × 10 ) were obtained by
n w
4
0
triethylene glycol (M ) was synthesized as previously reported.
2
polycondensation of BHF and SA with N,N′-diisopropylcarbo-
Other reagents and solvents were purchased from Wako Pure
Chemical Industry. All chemicals were used as received.
diimide as a condensation agent. PFSs were cross-linked with
M by the DA reaction between furan and maleimide. The F/M
ratio was set to 2/1, 3/1, 4/1, 6/1, 8/1, or 10/1. Hereafter, a
cross-linked sample with F/M ratio = x/1 is referred to as PFS/
Measurements. The 400 MHz 1H NMR spectra of solution
samples were obtained on a JEOL JNM-AL400 spectrometer. Gel
permeation chromatography was carried out with a Tosoh HLC-
2
M -x/1. PFS/M -2/1, -8/1, and -10/1 were prepared from PFS
8
220GPC equipped with two Shodex GPC LF-804 columns.
Polystyrene standards with low polydispersity were used to construct
2
2
with n = 24, and others were prepared from PFS with n = 27.
a calibration curve. Attenuated total reflection infrared (ATR-IR)
Because the properties of network polymers depend on the
B
dx.doi.org/10.1021/ma3023603 | Macromolecules XXXX, XXX, XXX−XXX