100 N load cell, using a flat dog bone-type specimen with an effective
gage length of 13 mm, a width of 2 mm, and a thickness of 1.3 mm. The
samples were cut out using a Ray-Ran dog bone cutter. The tensile tests
(Table S1, Supporting Information), with the soluble fraction of
the as-synthesized material being almost identical to that of the
material recycled 4 times. Furthermore, no chemical degrada-
tion was visible on ATR-FTIR, i.e., the IR-spectra after subse-
quent cycles are almost identical (Figure S11, Supporting Infor-
mation). In general, the vinylogous urethane networks exhib-
ited excellent recycling properties over four recycling cycles
without loss of mechanical properties or chemical changes.
were run at a speed of 10 mm min−1
.
Synthetic Procedures (Propyl Acetoacetate): 2,2,6-Trimethyl-4H-1,3-
dioxin-4-one (5.38 g, 34 mM) and 1-propanol (10 mL) were mixed in
a pressure tube and heated for 3 h at 135 °C. After the reaction was
finished according to thin layer chromatography (TLC), the excess of
1-propanol was removed in vacuo, yielding pure propyl acetoacetate.
Yield: 98%, 5.34 g. 1H NMR (300 MHz, CDCl3, δ): 4.10 (t, J = 6.5 Hz,
2H), 3.45 (s, 2H), 2.27 (s, 3H), 1.63 (m, 2H), 0.94 (t, J = 6.5 Hz, 3H).
Propyl-3-(butylamino)but-2-enoate and Propyl-3-(benzylamino)but-2-
enoate: Propyl acetoacetate (0.250 g, 1.73 mM) and butyl- or benzylamine
(2 eq, 3.47 mM) were dissolved in 5 mL of methanol and stirred
overnight. When the formation of the vinylogous urethane was complete
(TLC), the solvent was removed in vacuo and the mixture was extracted
twice with brine and CH2Cl2. The combined organic phases were dried
with MgSO4 and evaporated, yielding the desired product. The obtained
product was purified by flash chromatography using EtOAc/hexane
(25/75). Yield of propyl-3-(butylamino)but-2-enoate: 92%, 0,317 g. 1H
NMR (300 MHz, CDCl3, δ): 8.55 (s, 1H), 4.44 (s, 1H), 3.98 (t, J = 6.77
Hz, 2H), 3.20 (q, J = 6.52 Hz, 2H), 1.91 (s, 3H), 1.65−1.39 (m, 7H),
0.936 (t, J = 7.37 Hz, 6H).
3. Conclusion
In summary, the first catalyst-free vitrimers were developed
using the exchange reaction of amines on vinylogous ure-
thanes. These urethane-like chemical moieties emerge as
interesting bonds for building polymers, which combine
chemical robustness (thermal and hydrolytic stability) with
rapid exchange kinetics. Polymer networks were prepared
by bulk polymerization of cyclohexane dimethanol bisace-
toacetate, m-xylylene diamine, and tris(2-aminoethyl)amine.
Poly(vinylogous urethane) networks with a glass transition
temperature of 87 °C and a storage modulus of ≈2.4 GPa were
obtained. As expected for a polymer network, the samples were
insoluble even at elevated temperature while a rubbery plateau
was observed by DMA. Stress–relaxation and creep experi-
ments showed a viscoelastic liquid behavior. Due to the fast
exchange reactions and high density of exchangeable bonds
throughout the network, relaxation times as short as 85 s at
170 °C were achieved without the use of any catalyst. More-
over, the poly(vinylogous urethane) networks can be recycled
by grinding and without loss of mechanical properties. Since
the poly(vinylogous urethane) networks are made from easily
accessible chemicals, we expect that a wide range of materials
and applications can exploit this new chemistry for vitrimers.
Yield of Benzyl-3-(butylamino)but-2-enoate: 94%, 0,379 g. 1H NMR
(300 MHz, CDCl3, δ): 8.96 (s, 1H), 7.39−7.27 (m, 5H), 4.56 (s, 1H), 4.45
(d, J = 6.36, 2H), 4.02 (t, J = 6.76, 2H), 1.93 (s, 3H), 1.65 (tt, 2H), 0.96
(t, 7,42).
N-benzyl-3-(benzylamino)but-2-enamide: A solution of 2,2,6-trimethyl-
4H-1,3-dioxin-4-one (0.5 g, 3.52 mM) and benzylamine (1.13 g,
10.5 mM) in 1.5 mL of xylene was refluxed for 2 h. When the conversion
of the starting product was complete (TLC), the solvent was removed
under vacuum. The obtained mixture consisted mainly of N,N-
benzylacetoacetamide with a small fraction of N-benzyl-3-(benzylamine)
but-2-enamide, according to 1H NMR. This mixture was dissolved in
10 mL of MeOH and benzylamine (0.75 g, 7.04 mM) was added. The
mixture was stirred at room temperature over 48 h, resulting in a white
suspension. This suspension was poured in 25 mL of water and the
white precipitate was filtered off, washed with water, and dried to obtain
N-benzyl-3-(benzylamino)but-2-enamide. Yield: 85%, 0,83 g. 1H NMR
(300 MHz, CDCl3, δ): 9.53 (s, 1H), 7.38−7.24 (m, 10H), 4.47−4.39 (m,
5H), 1.89 (s, 3H).
1,4-Bis(hydroxymethyl)cyclohexane Bis-acetoacetate: 1,4 cyclohexane
dimethanol (88.9 g, 0.61 M) and tert-butyl acetoacetate (200 g, 1.26 M)
were dissolved in 120 mL of xylene in a 1 L flask equipped with a still
head and cooler. The mixture was heated for 90 min at 135 °C. The tert-
butanol product was removed by distillation during the reaction and the
temperature in the still head was typically between 75 and 90 °C. When
the temperature dropped to 50 °C, the mixture was cooled and the
solvent was removed in vacuo. The resulting crude product crystallized
upon cooling with ice and consisted of a 28:72 mixture of the cis- and
trans-isomers, as indicated by the singlets at 4.08 ppm for the cis-isomer
and 3.97 ppm for the trans-isomer. Recrystallization of the crude product
in isopropanol yielded 72% of white crystals, which consisted of 92% of
the trans-acetoacetate. Yield: 72%, 96.5 g. 1H NMR (300 MHz, CDCl3, δ):
4.09 (d, J = 7.19 Hz, 2H cis), 3.97 (d, 6.48 Hz, 2H trans), 3.47 (s, 2H),
2.28 (s, 3H), 1.83−1.78 (m, 4H), 1.68−1.62 (m, 2H), 1.05−1.01 (m, 4H).
Model Studies: Benzylamine (0.25 mM, 57 mg) was added to a
solution of N-butyl vinylogous urethane model compound (0.05 mM,
20 mg) in benzene-d6 (1.5 mL). Five equivalents of benzylamine were
used to obtain a pseudo-first order reaction at low conversions. The
mixture was heated (100, 120, and 140 °C) in a pressure tube and NMR
spectra were taken at different time intervals. The reaction was followed
by integration of the two distinct sharp signals at 4.77 ppm and 4.80 pm
for the N-butyl- and N-benzyl model compounds, respectively.
4. Experimental Section
Materials: 1-Propanol (>99.5%), butylamine (≥99%), benzylamine
(≥99%), m-xylylene diamine (≥99%), tris(2-aminoethyl)amine (96%),
cyclohexane dimethanol (mixture of cis and trans, 99%), 2,2,6-trimethyl-
4H-1,3-dioxinon-4-one (≥93%), and tert-butyl acetoacetate (≥98%) were
purchased from Sigma-Aldrich. 2,2,6-Trimethyl-4H-1,3-dioxin-4-one was
purified by distillation (0.2 Torr, 65–67 °C). The temperature was kept
below 90 °C to avoid decomposition.
Instrumentation: Nuclear magnetic resonance spectra were recorded
on a Bruker Avance 300 or a Bruker Avance II 700 spectrometer at
room temperature. IR spectra were collected using a Perkin–Elmer
Spectrum1000 FTIR infrared spectrometer with a diamond ATR probe.
Thermogravimetric analyses were performed with a Mettler Toledo TGA/
SDTA851e instrument under air or nitrogen atmosphere at a heating rate
of 10 °C min−1 from 25 °C to 500 °C. Differential scanning calorimetry
(DSC) analyses were performed with a Mettler Toledo instrument 1/700
under nitrogen atmosphere at a heating rate of 10 °C min-1. Dynamic
mechanical analysis (DMA) was performed on a SDTA861e DMA from
Mettler Toledo. Stress–relaxation experiments were conducted on a Ares
G2 rheometer from TA-instruments in torsion geometry with samples
of dimension (1.3 × 14.5 × 22 mm3). An axial force of −0.01 N and a
deformation of 1% were applied. Creep experiments were performed on
rectangular samples (5 mm × 1.4 mm × 10 mm) by using a TA-Q800
DMA; a constant stress of 0.1 MPa was applied. Tensile testing was
performed on a Tinius–Olsen H10KT tensile tester, equipped with a
Network Synthesis: Xylylene diamine (2.111 g, 15.5 mM), tris(2-
aminoethyl)amine (1.774 g, 12.1 mM), and 1,4-cyclohexanedimethanol
bisacetoacetate (10 g, 32.0 mM) were mixed in a vial and heated in an oil
bath thermostated at 80 °C. When a homogeneous liquid mixture was
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2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2015,
DOI: 10.1002/adfm.201404553