Macromolecules
Article
flame-dried round-bottom flask charged with a stir bar and THF (52
mL). To the clear reaction mixture, n-BuLi (3.54 mL, 9.38 mmol, 2.5
M in cyclohexanes) was added dropwise at −78 °C. After 15 min,
chlorotrimethylsilane (1.17 mL, 9.26 mmol) was added dropwise to
the reaction mixture at −78 °C, and the mixture was allowed to warm
to 0 °C for 15 min. The mixture was cooled again to −78 °C and
transferred carefully to a solution of freshly prepared LDA (20.3
mmol) at −78 °C. After 30 min, allyl bromide (1.87 mL, 22.1 mmol)
was added at −78 °C dropwise, followed by warming to room
temperature and stirring under a nitrogen atmosphere for 5 h. The
mixture was quenched by addition of saturated aqueous ammonium
chloride solution followed by addition of ethyl acetate. The organic
phase was separated and dried over anhydrous sodium sulfate, filtered,
and concentrated under reduced pressure. The crude product isolated
from that process was purified by column chromatography on silica
gel, eluting with a 3:2 mixture of hexanes and ethyl acetate and then a
1:1 mixture of the same solvents, affording the desired product, after
removal of solvents by evaporation, as a white powder in ∼85% yield.
1H NMR (500 MHz, CDCl3, δ, ppm): δ 5.79 (m, 1H), 4.98 (m, 2H),
TFE, and the cross-linked polymers did not swell in water but
swelled rapidly in TFE.
In summary, a series of novel, allyl-substituted aliphatic
polyamides were prepared by anionic ring-opening copoly-
merization involving an allyl-functionalized ε-caprolactam
monomer. By adjusting mole percentages of allyl groups, the
crystallinity, melting temperature (Tm), and crystallization
temperature (Tc) of the polymers were modulated accordingly.
The alkene moieties were easily converted into the desired
chemical functionalities with high efficiency thiol−ene “click”
reactions, using a variety of mono- and multifunctional thiols
providing a modular method to a tremendous variety of
functional polyamide-6 derivatives. The ability to alter both
crystallinity and reactivity of these polymers will open new
opportunities in thermoplastics and other application areas.
Despite that incorporation of high mole percentages of
functional groups into these polymers was not achieved, the
levels that were realized are sufficient to significantly alter
physical and chemical properties. This work represents an
exceptionally simple and effective approach to functional
polyamide copolymers and will open new opportunities for
such structures in composite materials and blends.
3.22 (m, 2H), 2.54 (m, 1H), 2.41−2.02 (m, 2H), 1.92−1.32 (m,
10H). 13C NMR (CDCl3, 126 MHz): δ 179.6, 137.2, 116.5, 43.4,
42.4, 35.9, 29.8, 29.6, 29.2.
General Procedure for Anionic Ring-Opening Copolymer-
ization. Prior to polymerization, the reagents were subjected to
vacuum for ∼8 h, and the glass reaction tube was flame-dried.
Synthesis of P4. Monomer 1 (370 mg, 2.40 mmol), ε-caprolactam
(1.70 g, 15.5 mmol), and initiator C10 (319 mg, 0.40 mmol) were
added to the flask, and the system was purged with nitrogen for 30
min (Figure 2b). The polymerization tube was heated by placement
into an oil bath that was preheated to 140 °C. After melting the
contents of the tube, activator C20 (138 mg, 0.06 mmol) was added
to the reaction mixture, and the polymerization was performed for 30
min under a nitrogen atmosphere. Multiple polymerizations were
carried out, side-by-side, in polymerization tubes, and aliquots were
withdrawn at different time intervals, with monomer conversion
monitored by 1H NMR spectroscopy and molecular weight evaluation
evaluated by GPC. To terminate the polymerization, the tube was
simply allowed to cool to room temperature.
EXPERIMENTAL SECTION
■
Materials. Aza-2-cycloheptanone (99%), chlorotrimethylsilane
(≥99%), n-butyllithium (2.5 M in cyclohexane), n-butyllithium (2
M in cyclohexane), diisopropylamine (99.95%), allyl bromide (99%),
mercaptoethanol (≥99%), 4-bromobenzyl mercaptan (97%), pentaer-
ythritol tetrakis(3-mercaptopropionate) (>95%), 2,2-dimethoxy-2-
phenylacetophenone (99%), 1,3-propanedithiol (99%),
1H,1H,2H,2H-perfluorodecanethiol (97%), and 9-fluorenylmethylth-
iol (97%) were purchased from Aldrich and used without further
purification. 2,2,2-Trifluoroethanol was purchased from Alfa Aesar
and used without further purification. 2-Methacryloyloxyethyl-
phosphorylcholine (MPC) was purchased from Aldrich and washed
with diethyl ether prior to use. Sodium caprolactamate (Bru
̈
ggolen
C10) and hexamethylene-1,6-dicarbamoylcaprolactam (Bruggolen
̈
For purification, the polymer was solubilized in hot TFE, followed
by precipitation in ethyl acetate. Precipitation was performed multiple
times to remove any excess monomer or other impurity, and the
precipitated polymer was dried under high vacuum to isolate the
polyamides as white, fibrous solids.
C20) were obtained from Bruggemann and used without further
purification. Anhydrous THF was purified by distillation over
benzophenone and sodium metal. Deuterated solvents for NMR
spectroscopy were purchased from Cambridge Isotope Laboratories.
Chloroform, methanol, tetrahydrofuran, dichloromethane, sodium
sulfate, hexane, diethyl ether, and ethyl acetate were purchased from
Fisher Scientific.
1
P4: H NMR (500 MHz, TFE-d3, δ, ppm): δ 5.50 (1.02H), 4.81
(2.00H), 2.97 (19.96H), 2.10−1.97 (20.81H), 1.41−1.21 (40.47H),
1.11 (20.89H). 13C NMR (CDCl3, 126 MHz, δ, ppm): δ 179.6, 137.2,
116.5, 43.4, 42.4, 35.9, 29.8, 29.6, 29.2.
1
Instrumentation. H NMR spectra were recorded on a Bruker
Avance-500 spectrometer operating at 500 MHz, and chemical shifts
reported in ppm were calibrated to residual solvent signals. 13C NMR
and 13P NMR spectra were recorded on a Bruker Avance-500
spectrometer operating at 126 and 202 MHz, respectively. Gel
Example Procedure for Thiol−Ene Reactions. Allyl-functionalized
polyamide P4 was dissolved in minimum amount of TFE in a 20 mL
glass scintillation vial charged with a stir bar. The respective thiols (3
equiv relative to alkene) and DMPA (0.3 equiv) were added to as
solids. The mixture was solubilized and degassed with nitrogen for
10−20 min. The stirring reaction mixture was exposed to 365 nm
(∼3.5 mW/cm2) light in a UV cross-linker chamber (model: CL-
1000L, UVP, Upland, CA) for 2 h at room temperature.
P4a, P4b, P4d, and P4e were purified by precipitation in ethyl
acetate to afford off-white solid products with a typical yield of ≤95%.
Phosphorylcholine-substituted polyamide P4c was purified by
precipitation in THF, followed by dialysis against water and
lyophilizing to obtain a white fluffy product with a yield of 85−90%.
P4f, the organogel, was obtained by solubilizing 50 mg of P4
(SH:alkene 3:1) in the presence of DMPA in TFE, degassing with
nitrogen for 10 min, and exposing to 365 nm UV light for 10 min.
P4g, the polymeric film, was obtained by dropcasting the polymeric
mixture (P4c) before UV exposure on a glass substrate and
evaporating the solvent under the stream of nitrogen and exposing
to 365 nm for 10 min.
ο
permeation chromatography was performed at 40 C using 0.02 M
sodium trifluoroacetate in TFE as eluent at a flow rate of 1 mL min−1
with three Agilent PL gel mixed columns (300 × 7.5 mm2), refractive
index (RI) detection, and calibration against PMMA standards.
Thermogravimetric analysis (TGA) was performed on a Q500 TA
Instruments with a heating rate of 20 °C/min under a nitrogen
atmosphere, heating from 0 to 600 °C with a gas flow rate of 200 mL/
min. Melting temperature (Tm) and crystallization temperature (Tc)
were determined by differential scanning calorimetry (DSC) on a
Q200 TA Instruments under a nitrogen atmosphere (method: heat
from −20 to 260 °C at 10 °C/min, hold at 260 °C for 2 min, cool
from 260 °C to −20 °C at 10 °C/min, and heat from −20 °C to 260
°C at 10 °C/min). Fourier-transform infrared (FT-IR) spectra were
recorded on a PerkinElmer Spectrum 100 spectrometer with
attenuated total reflectance (ATR).
Synthesis of 3-(3-Propenyl)-2-azepanone (Monomer 1).
Monomer 1 was synthesized per the previous literature with some
modifications.24 ε-Caprolactam (1 g, 8.86 mmol) was added to a
G
Macromolecules XXXX, XXX, XXX−XXX