Diversely Substituted Polyamides: Macromolecular Design Using the

Article pubs.acs.org/Macromolecules

Diversely Substituted Polyamides: Macromolecular Design Using the Ugi Four-Component Reaction Ansgar Sehlinger, Patrick-Kurt Dannecker, Oliver Kreye, and Michael A. R. Meier* Laboratory of Applied Chemistry, Institute of Organic Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany S Supporting Information *

ABSTRACT: A novel strategy is demonstrated to obtain polyamides with finely tunable structure using the Ugi fourcomponent reaction (Ugi-4CR). By the use of two bifunctional and two monofunctional components, six different combinations for the synthesis of polyamides via the Ugi-4CR are possible and were investigated in detail within this contribution. In contrast to conventional polyamide synthesis, this approach proceeds under very mild reaction conditions and without the use of a catalyst in a one-pot reaction. General applicability is shown by variation of the components, leading to finely tuned macromolecular structures (i.e., side groups and repeat units can be engineered). Finally, a facile introduction of clickable alkyne moieties is demonstrated, which was used for post-polymerization modification in an azide−alkyne cycloaddition, in order to demonstrate the high versatility of this approach. example, more elastic.9 Furthermore, post-polymerization modifications of functionalized polyamides have been shown.10 In this study, we demonstrate a very efficient and modular approach to synthesize diversely substituted polyamides via the Ugi four-component reaction (Ugi-4CR).11 This reaction belongs to the class of multicomponent reactions (MCRs), which recently gained great attention in polymer science.12,13 By the use of bifunctional components, MCRs can produce polymers in a polycondensation or polyaddition processes. For example, the Passerini three-component reaction (Passerini3CR) was used to synthesize polyesters having amide side chains, polyamides having ester side chains, or poly(ester− amide)s. 14−19 Apart from the isocyanide-based MCRs (IMCRs), metal-catalyzed MCRs have been developed for step-growth polymerizations. Tang et al. presented the synthesis of functional macromolecules with well-defined structures by a transition-metal-catalyzed three-component polycoupling of alkynes, aldehydes, and amines.20 Moreover, Choi et al. introduced a copper-catalyzed multicomponent polymerization of diynes, sulfonylazides, and diamines that resulted in poly(N-sulfonylamidines) exhibiting highly regular structures.21 Furthermore, a palladium-catalyzed multicomponent reaction was developed by Arndtsen et al. involving imines, diimines, and di(acyl chloride)s resulting in πconjugated imidazole-based oligomers.22 In this context, the Ugi-4CR was only applied once to cross-link alginate using 1,5-

1. INTRODUCTION Polyamides represent an important class of polymers in nature and for industrial applications. Natural polyamides occur as peptides and proteins in organisms accomplishing essential body functions. Furthermore, these resources provide the raw material for the production of silk and wool, which have been used by mankind for millennia. However, synthetic polyamides made their way as indispensable materials in the textile and automotive industry. First discovered in 1935, W. H. Carothers reacted adipic acid and hexamethylenediamine to synthesize stretchable fibers of high strength, later merchandized as nylon.1 Polyamides are mainly obtained by polycondensation or ringopening procedures. In the former case, AA- and BB-type or AB-type monomers can be applied. Here, well-known representatives are PA 6.6 (nylon) and PA 11. The latter is obtained from ω-aminododecanoic acid, a castor oil derived chemical.2 In contrast, ring-opening polymerizations occur without elimination of small molecules and they profit from ring-strain release. The most employed lactams are εcaprolactam and laurolactam leading to PA 6 and PA 12, respectively.3,4 Both polyamide synthesis routes need very high temperatures due to the high melting points (170−260 °C) of the polymers, and depending on the process, high pressure or sometimes vacuum is applied.5 The resulting polyamides (usually aliphatic) exhibit chemical and temperature resistance, mechanical strength, toughness, and durability. Later on, N-substituted polyamides have been introduced, which possess lower melting points due to their reduced number of hydrogen bonds.6−8 This makes the polymers, for © 2014 American Chemical Society

Received: March 9, 2014 Revised: April 22, 2014 Published: April 28, 2014 2774

dx.doi.org/10.1021/ma500504w | Macromolecules 2014, 47, 2774−2783

Macromolecules

Article

diaminopentane as bifunctional linker.23 Apart from polycondensation reactions, it was already used for monomer design and as for block copolymer synthesis.24−26 Within this contribution, all possible combinations for an Ugi step-growth polymerization process were investigated for the first time and in detail in order to synthesize structurally diverse polyamides. The combinatorial nature of MCRs offers the opportunity for modular design and easy post-polymerization modifications.

SEC-ESI-MS spectra were recorded on a LXQ mass spectrometer (Thermo Fisher Scientific, San Jose, CA) equipped with an atmospheric pressure ionization source operating in the nebulizerassisted electrospray mode. The instrument was calibrated in the m/z range 195−1822 using a standard containing caffeine, Met-Arg-PheAla acetate (MRFA), and a mixture of fluorinated phosphazenes (Ultramark 1621) (all from Aldrich). A constant spray voltage of 4.5 kV, a dimensionless sweep gas flow rate of 2, and a dimensionless sheath gas flow rate of 12 were applied. The capillary voltage, the tube lens offset voltage, and the capillary temperature were set to 60 V, 110 V, and 275 °C, respectively. The LXQ was coupled to a Series 1200 HPLC-system (Agilent, Santa Clara, CA) consisting of a solvent degasser (G1322A), a binary pump (G1312A), and a high-performance autosampler (G1367B), followed by a thermostated column compartment (G1316A). Separation was performed on two mixed bed size exclusion chromatography columns (Polymer Laboratories, Mesopore 2504.6 mm, particle diameter 3 μm) with precolumn (Mesopore 50−4.6 mm) operating at 30 °C. THF at a flow rate of 0.30 mL/min was used as eluent. The mass spectrometer was coupled to the column in parallel to an RI detector (G1362A with SS420x A/ D) in a setup described previously, 0.27 mL/min of the eluent was directed through the RI detector, and 30 μL/min was infused into the electrospray source after post column addition of a 100 μM solution of sodium iodide in methanol at 20 μL/min by a microflow HPLC syringe pump (Teledyne ISCO, Model 100DM). 20 μL of a polymer solution with a concentration of ∼3 mg/mL was injected onto the HPLC system. GC-MS (electron impact (EI)) measurements were performed on the following system: a Varian 431 GC instrument with a capillary column FactorFour VF-5 ms (30 m × 0.25 mm × 0.25 mm) and a Varian 210 ion trap mass detector. Scans were performed from 40 to 650 m/z at rate of 1.0 scans/s. The oven temperature program was: initial temperature 95 °C, hold for 1 min, ramp at 15 °C/min to 220 °C, hold for 4 min, ramp at 15 °C/min to 300 °C, hold for 2 min. The injector transfer line temperature was set to 250 °C. Measurements were performed in the split−split mode (split ratio 50:1) using helium as carrier gas (flow rate 1.0 mL/min). 2.3. Ugi-4CR Polycondensations. 2.3.1. Polymer Derived from Hexamethylenediamine, Sebacic Acid, Isobutyraldehyde, and tertButyl Isocyanide (20). A solution of hexamethylenediamine (116 mg, 1.00 mmol) and isobutyraldehyde (159 mg, 201 μL, 2.20 mmol) in 0.5 mL of methanol was stirred at room temperature for 1 h. THF (1.0 mL), tert-butyl isocyanide (183 mg, 249 μL, 2.20 mmol), and sebacic acid (202 mg, 1.00 mmol) were added. The mixture was stirred for 37 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in icecold diethyl ether yielded colorless polymer 20 (411 mg, 69%). 1H NMR (CDCl3, 300 MHz): δ = 0.77 (d, J = 6.5 Hz, 6 H, 2 CHCH3), 0.94 (d, J = 6.3 Hz, 6 H, 2 CHCH3), 1.15−1.72 (m, 20 H, 10 CH2), 1.29 (s, 18 H, 2 t-Bu), 2.19−2.46 (m, 6 H, 2 COCH2, 2 CHCH3), 3.10−3.35 (m, 4 H, 2 CH2N), 4.10 (br, 2 H, 2 NCH), 6.49 (br, 2 H, 2 NH) ppm; Tg = 60 °C. 2.3.1.1. Polymer Derived from 1,12-Diaminododecane, Sebacic Acid, Isobutyraldehyde, and tert-Butyl Isocyanide (21). A solution of 1,12-diaminododecane (200 mg, 1.00 mmol) and isobutyraldehyde (173 mg, 219 μL, 2.40 mmol) in 0.8 mL of methanol was stirred at room temperature for 1 h. THF (1.6 mL), tert-butyl isocyanide (200 mg, 271 μL, 2.40 mmol), and sebacic acid (202 mg, 1.00 mmol) were added. The mixture was stirred for 64 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in hexane (ambient temperature) yielded colorless polymer 21 (447 mg, 66%). 1H NMR (CDCl3, 300 MHz): δ = 0.76 (d, J = 6.5 Hz, 6 H, 2 CHCH3), 0.93 (d, J = 6.3 Hz, 6 H, 2 CHCH3), 1.07−1.74 (m, 32 H, 16 CH2), 1.28 (s, 18 H, 2 t-Bu), 2.18−2.47 (m, 6 H, 2 COCH2, 2 CHCH3), 3.11−3.35 (m, 4 H, 2 CH2N), 4.07 (br, 2 H, 2 NCH), 6.52 (br, 2 H, 2 NH) ppm; Tg = 39 °C. 2.3.2. Polymer Derived from Hexamethylenediamine, 1,6Diisocyanohexane, Isobutyraldehyde, and Hexanoic Acid (22). A solution of hexamethylenediamine (116 mg, 1.00 mmol) and

2. EXPERIMENTAL SECTION 2.1. Materials. The following chemicals were used as received: hexanoic acid 1 (98%, Cognis), isobutyraldehyde 2 (≥98%, Aldrich), n-butylamine 3 (99.5%, Aldrich), tert-butyl isocyanide 4 (98%, Aldrich), sebacic acid 6 (99%, Aldrich), 10-undecenoic acid (98%, Aldrich), (1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(o-isopropoxyphenylmethylene)ruthenium (Hoveyda− Grubbs catalyst of the second generation, Aldrich), 1,4-benzoquinone (>99%, Aldrich), ethyl vinyl ether (99%, Aldrich), palladium on activated charcoal (10% Pd, Aldrich), lithium hydroxide (98%, Aldrich), hexamethylenediamine 8 (98%, Aldrich), 1,12-diaminododecane 9 (98%, Aldrich), ethyl formate (≥97%, Aldrich), diisopropylamine (>99%, Aldrich), phosphoryl chloride (99%, Aldrich), terephthalaldehyde 12 (99%, Aldrich), 10-undecenal 14 (≥90%, Aldrich), propylamine 15 (98%, Aldrich), ethyl 2-methyl-4-pentenoate 18 (98%, Aldrich), lithium aluminum hydride solution (1 M in THF, Aldrich), dimethyl sulfoxide (anhydrous ≥99.9%, Aldrich), oxalyl chloride (98%, Aldrich), triethylamine (99%, Acros Organics), 5hexynoic acid 35 (97%, Acros), diethylene glycol methyl ether (≥98%, Aldrich), methanesulfonyl chloride (≥99.7%, Aldrich), sodium azide (reagent grade, Fisher scientific), copper(I) bromide (99.999%, Aldrich), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA, 99%, Aldrich), silica gel 60 (0.035−0.070, Aldrich), chloroform-d (CDCl3, 99.8 atom % D, Euriso-Top), dimethyl-d6 sulfoxide (99.8 atom % D, Euriso-Top). All solvents were used without any kind of purification unless otherwise noted. Only water was used in a deionized form. 2.2. Characterization. NMR spectra were recorded on a Bruker AVANCE DPX spectrometer operating at 300 MHz for 1H and at 75 MHz for 13C measurements. CDCl3 was used as solvent and the resonance signal at 7.26 ppm (1H) and 77.16 ppm (13C) served as reference for the chemical shift δ. Polymers were characterized on a SEC System LC-20A (Shimadzu) equipped with a SIL-20A autosampler and a RID-10A refractive index detector in THF (flow rate 1 mL/min) at 50 °C. The analysis was performed on the following column system: main-column PSS SDV analytical (5 μm, 300 mm × 8.0 mm, 10000 Å) with a PSS SDV analytical precolumn (5 μm, 50 mm × 8.0 mm). For the calibration narrow linear poly(methyl methacrylate) standards (Polymer Standards Service PPS, Germany) ranging from 1100 to 981 000 Da were used. The thermal properties of the prepared polymers were studied via differential scanning calorimetry (DSC) with a Mettler Toledo DSC stare system operating under nitrogen atmosphere using about 5 mg of the respective polymer for the analysis. The glass transition (Tg) was recorded on the second heating scan by using the following method: heating from −70 to 150 °C at 20 °C/min, cooling from 150 °C to −75 °C at 20 °C/min, and heating from −75 to 150 °C at 10 °C/min. Infrared spectra (IR) were recorded on a Bruker Alpha-p instrument in a frequency range from 3998 to 374 cm−1 applying KBR and ATR technology. Fast atom bombardment (FAB) mass spectra were recorded on a Finnigan MAT 95 instrument. The protonated molecular ion is expressed by the term: [(M + H)]+. All thin layer chromatography experiments were performed on silica gel coated aluminum foil (silica gel 60 F254, Aldrich). Compounds were visualized by irradiation with a UV lamp or by staining with Seebach solution (mixture of phosphomolybdic acid hydrate, cerium(IV) sulfate, sulfuric acid, and water). 2775


Macromolecules

Article

isobutyraldehyde (216 mg, 274 μL, 3.00 mmol) in 1.13 mL of methanol was stirred at room temperature for 1 h. THF (0.57 mL), 1,6-diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and hexanoic acid (348 mg, 375 μL, 3.00 mmol) were added. The mixture was stirred for 42 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in diethyl ether (ambient temperature, twice) yielded colorless polymer 22 (321 mg, 54%). 1H NMR (CDCl3, 300 MHz): δ = 0.79 (d, J = 6.4 Hz, 6 H, 2 CHCH3), 0.84−1.04 (m, 12 H, 2 CHCH3, 2 CH3), 1.15− 1.81 (m, 28 H, 14 CH2), 2.17−2.63 (m, 6 H, 2 COCH2, 2 CHCH3), 3.01−3.44 (m, 8 H, 4 CH2N), 4.08 (br, 2 H, 2 NCH), 6.89 (br, 2 H, 2 NH) ppm; Tg = 65 °C. 2.3.2.1. Polymer Derived from 1,12-Diaminododecane, 1,6Diisocyanohexane, Isobutyraldehyde, and Hexanoic Acid (23). A solution of 1,12-diaminododecane (200 mg, 1.00 mmol) and isobutyraldehyde (216 mg, 274 μL, 3.00 mmol) in 1.13 mL of methanol was stirred at room temperature for 1 h. THF (0.57 mL), 1,6-diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and hexanoic acid (348 mg, 375 μL, 3.00 mmol) were added. The mixture was stirred for 64 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in diethyl ether (ambient temperature) yielded colorless, sticky polymer 23 (639 mg, 94%). 1H NMR (CDCl3, 300 MHz): δ = 0.80 (d, J = 6.5 Hz, 6 H, 2 CHCH3), 0.84−0.99 (m, 12 H, 2 CHCH3, 2 CH3), 1.11− 1.73 (m, 40 H, 20 CH2), 2.20−2.59 (m, 6 H, 2 COCH2, 2 CHCH3), 3.04−3.36 (m, 8 H, 4 CH2N), 4.00 (br, 2 H, 2 NCH), 6.90 (br, 2 H, 2 NH) ppm; Tg = 21 °C. 2.3.3. Polymer Derived from Sebacic Acid, 1,6-Diisocyanohexane, Isobutyraldehyde, and Propylamine (24). A solution of propylamine (177 mg, 247 μL, 3.00 mmol) and isobutyraldehyde (216 mg, 274 μL, 3.00 mmol) in 0.5 mL of methanol was stirred at room temperature for 1 h. THF (1.0 mL), 1,6-diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and sebacic acid (202 mg, 1.00 mmol) were added. The mixture was stirred for 64 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in diethyl ether (ambient temperature) yielded colorless polymer 24 (426 mg, 75%). 1H NMR (CDCl3, 300 MHz): δ = 0.78 (d, J = 6.5 Hz, 6 H, 2 CHCH3), 0.85 (t, J = 7.3 Hz, 6 H, 2 CH3), 0.92 (d, J = 6.4 Hz, 6 H, 2 CHCH3), 1.15−1.73 (m, 24 H, 12 CH2), 2.18−2.60 (m, 6 H, 2 COCH2, 2 CHCH3), 3.04−3.31 (m, 8 H, 4 CH2N), 4.05 (br, 2 H, 2 NCH), 6.93 (br, 2 H, 2 NH) ppm; Tg = 42 °C. 2.3.3.1. Polymer Derived from Icosanedioic Acid, 1,6-Diisocyanohexane, Isobutyraldehyde, and Propylamine (25). A solution of propylamine (177 mg, 247 μL, 3.00 mmol) and isobutyraldehyde (216 mg, 274 μL, 3.00 mmol) in 0.5 mL of methanol was stirred at room temperature for 1 h. THF (1.0 mL), 1,6-diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and icosanedioic acid (343 mg, 1.00 mmol) were added. The mixture was stirred for 64 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in diethyl ether (ambient temperature) yielded yellowish, sticky polymer 25 (535 mg, 79%). 1H NMR (CDCl3, 300 MHz): δ = 0.80 (d, J = 6.5 Hz, 6 H, 2 CHCH3), 0.86 (t, J = 7.3 Hz, 6 H, 2 CH3), 0.94 (d, J = 6.4 Hz, 6 H, 2 CHCH3), 1.14−1.74 (m, 44 H, 22 CH2), 2.21−2.61 (m, 6 H, 2 COCH2, 2 CHCH3), 3.07− 3.32 (m, 8 H, 4 CH2N), 4.03 (br, 2 H, 2 NCH), 6.91 (br, 2 H, 2 NH) ppm; Tg = 19 °C. 2.3.4. Polymer Derived from Sebacic Acid, 2,7-Dimethyloctanedial, tert-Butyl Isocyanide, and Propylamine (26). A solution of propylamine (130 mg, 181 μL, 2.20 mmol) and 2,7-dimethyloctanedial (170 mg, 1.00 mmol) in 1.0 mL of methanol was stirred at room temperature for 1 h. THF (0.5 mL), tert-butyl isocyanide (183 mg, 249 μL, 2.20 mmol), and sebacic acid (202 mg, 1.00 mmol) were added. The mixture was stirred for 41 h. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in hexane (ambient temperature) yielded colorless polymer 26 (435 mg, 68%). 1H NMR (CDCl3, 300 MHz): δ = 0.73 (d, J = 6.4 Hz, 3 H, CHCH3), 0.79−0.95 (m, 9 H, 2 CH3, CHCH3), 0.99−1.89 (m, 24 H, 12 CH2), 1.29 (s, 18 H, 2 t-Bu), 2.09−2.46 (m, 6 H, 2 COCH2, 2

CHCH3), 3.05−3.33 (m, 4 H, 2 CH2N), 4.12 (br, 2 H, 2 NCH), 6.56 (br, 2 H, 2 NH) ppm; Tg = 59 °C. 2.3.4.1. Polymer Derived from Icosanedioic Acid, 2,7-Dimethyloctanedial, tert-Butyl Isocyanide, and Propylamine (27). A solution of propylamine (130 mg, 181 μL, 2.20 mmol) and 2,7dimethyloctanedial (170 mg, 1.00 mmol) in 1.2 mL of methanol was stirred at room temperature for 1 h. THF (0.6 mL), tert-butyl isocyanide (183 mg, 249 μL, 2.20 mmol), and icosanedioic acid (342 mg, 1.00 mmol) were added. The mixture was stirred for 64 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in ice-cold hexane yielded colorless polymer 27 (544 mg, 72%). 1H NMR (CDCl3, 300 MHz): δ = 0.73 (d, J = 6.3 Hz, 3 H, CHCH3), 0.78−0.95 (m, 9 H, 2 CH3, CHCH3), 0.96−1.75 (m, 44 H, 22 CH2), 1.29 (s, 18 H, 2 t-Bu), 2.13−2.43 (m, 6 H, 2 COCH2, 2 CHCH3), 3.05−3.33 (m, 4 H, 2 CH2N), 4.11 (br, 2 H, 2 NCH), 6.54 (br, 2 H, 2 NH) ppm; Tg = 25 °C. 2.3.5. Polymer Derived from 1,6-Diisocyanohexane, 2,7-Dimethyloctanedial, Hexanoic Acid, and Propylamine (28). A solution of propylamine (236 mg, 329 μL, 4.00 mmol) and 2,7dimethyloctanedial (170 mg, 1.00 mmol) in 0.75 mL of methanol was stirred at room temperature for 1 h. THF (0.75 mL), 1,6diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and hexanoic acid (464 mg, 499 μL, 4.00 mmol) were added. The mixture was stirred for 40 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in hexane (ambient temperature, twice) yielded colorless polymer 28 (457 mg, 74%). 1H NMR (CDCl3, 300 MHz): δ = 0.75 (d, J = 6.2 Hz, 3 H, CHCH3), 0.81−0.97 (m, 15 H, 4 CH3, CHCH3), 1.06−1.73 (m, 32 H, 16 CH2), 2.19−2.45 (m, 6 H, 2 COCH2, 2 CHCH3), 3.06−3.33 (m, 8 H, 4 CH2N), 4.14 (br, 2 H, 2 NCH), 6.86 (br, 2 H, 2 NH) ppm; Tg = 23 °C. 2.3.5.1. Polymer Derived from 1,12-Diisocyanododecane, 2,7Dimethyloctanedial, Hexanoic Acid, and Propylamine (29). A solution of propylamine (236 mg, 329 μL, 4.00 mmol) and 2,7dimethyloctanedial (170 mg, 1.00 mmol) in 0.75 mL of methanol was stirred at room temperature for 1 h. THF (0.75 mL), 1,6diisocyanododecane (220 mg, 1.00 mmol), and hexanoic acid (464 mg, 499 μL, 4.00 mmol) were added. The mixture was stirred for 38 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in hexane (ambient temperature) yielded colorless, sticky polymer 29 (622 mg, 88%). 1H NMR (CDCl3, 300 MHz): δ = 0.74 (d, J = 6.2 Hz, 3 H, CHCH3), 0.79−0.98 (m, 15 H, 4 CH3, CHCH3), 1.02−1.73 (m, 44 H, 22 CH2), 2.17−2.45 (m, 6 H, 2 COCH2, 2 CHCH3), 3.05−3.32 (m, 8 H, 4 CH2N), 4.06 (br, 2 H, 2 NCH), 6.82 (br, 2 H, 2 NH) ppm; Tg = 1.0 °C. 2.3.6. Polymer Derived from Hexamethylenediamine, 2,7Dimethyloctanedial, Hexanoic Acid, and tert-Butyl Isocyanide (30). A solution of hexamethylenediamine (116 mg, 1.00 mmol) and 2,7-dimethyloctanedial (170 mg, 1.00 mmol) in 0.75 mL of THF was stirred at room temperature for 1 h. tert-Butyl isocyanide (183 mg, 249 μL, 2.20 mmol), hexanoic acid (256 mg, 275 μL, 2.20 mmol), and methanol (0.75 mL) were added. The mixture was stirred for 40 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in hexane (ambient temperature, twice) yielded colorless polymer 30 (401 mg, 62%). 1H NMR (CDCl3, 300 MHz): δ = 0.72 (d, J = 5.9 Hz, 3 H, CHCH3), 0.82−0.96 (m, 9 H, 2 CH3, CHCH3), 1.02−1.74 (m, 28 H, 14 CH2), 1.29 (s, 18 H, 2 t-Bu), 2.08−2.47 (m, 6 H, 2 COCH2, 2 CHCH3), 3.03−3.40 (m, 4 H, 2 CH2N), 4.18 (br, 2 H, 2 NCH), 6.45 (br, 2 H, 2 NH) ppm; Tg = 43 °C. 2.3.6.1. Polymer Derived from 1,12-Diaminododecane, 2,7Dimethyloctanedial, Hexanoic Acid, and tert-Butyl Isocyanide (31). A solution of 1,12-diaminododecane (200 mg, 1.00 mmol) and 2,7-dimethyloctanedial (170 mg, 1.00 mmol) in 0.75 mL of THF was stirred at room temperature for 1 h. tert-Butyl isocyanide (183 mg, 249 μL, 2.20 mmol), hexanoic acid (256 mg, 275 μL, 2.20 mmol), and methanol (0.75 mL) were added. The mixture was stirred for 40 h at room temperature. The solvent was removed in vacuo, and the residue 2776


Macromolecules

Article

dissolved in 1.5 mL of dichloromethane. Precipitation in ice-cold hexane yielded colorless, sticky polymer 31 (659 mg, 90%). 1H NMR (CDCl3, 300 MHz): δ = 0.72 (d, J = 5.8 Hz, 3 H, CHCH3), 0.78−0.97 (m, 9 H, 2 CH3, CHCH3), 1.05−1.75 (m, 40 H, 20 CH2), 1.29 (s, 18 H, 2 t-Bu), 2.11−2.47 (m, 6 H, 2 COCH2, 2 CHCH3), 3.05−3.37 (m, 4 H, 2 CH2N), 4.15 (br, 2 H, 2 NCH), 6.50 (br, 2 H, 2 NH) ppm; Tg = 25 °C. 2.3.7. Polymer Derived from 1,12-Diaminododecane, 1,6Diisocyanohexane, Isobutyraldehyde, and 5-Hexynoic Acid (32). A solution of 1,12-diaminododecane (200 mg, 1.00 mmol) and isobutyraldehyde (216 mg, 274 μL, 3.00 mmol) in 1.13 mL of methanol was stirred at room temperature for 1 h. THF (0.57 mL), 1,6-diisocyanohexane (136 mg, 152 μL, 1.00 mmol), and 5-hexynoic acid (336 mg, 331 μL, 3.00 mmol) were added. The mixture was stirred for 42 h at room temperature. The solvent was removed in vacuo, and the residue dissolved in 1.5 mL of dichloromethane. Precipitation in diethyl ether (ambient temperature) yielded colorless, sticky polymer 32 (575 mg, 86%). 1H NMR (CDCl3, 300 MHz): δ = 0.81 (d, J = 6.4 Hz, 6 H, 2 CHCH3), 0.94 (d, J = 6.3 Hz, 6 H, 2 CHCH3), 1.11−1.68 (m, 28 H, 14 CH2), 1.80−1.95 (m 4 H, 2 HC CCH2CH2), 1.96−2.02 (m, 2 H, HCC), 2.27 (td, J = 6.6, 2.3 Hz, 4 H, HCCCH2), 2.36−2.63 (m, 6 H, 2 COCH2, 2 CHCH3), 2.99− 3.45 (m, 8 H, 4 CH2N), 4.05 (br, 2 H, 2 NCH), 6.84 (br, 2 H, 2 NH) ppm; Tg = 15 °C. 2.3.7.1. Azide−Alkyne coupling of Alkyne-Functionalized Polymer 32 and 1-Azido-2-(2-methoxyethoxy)ethane 33 Resulting in Polymer 34. Polymer 32 (100 mg, 0.15 mmol), 1-azido-2-(2methoxyethoxy)ethane 33 (61.0 mg, 0.42 mmol, 1.40 equiv), PMDETA (10.4 mg, 12.5 μL, 0.06 mmol, 0.20 equiv), and 1.0 mL of THF were placed in a round-bottomed flask. Afterward, the reaction mixture was degassed with argon for 10 min and copper(I) bromide (8.61 mg, 0.06 mmol, 0.20 equiv) was added. The reaction was run for 48 h at room temperature and subsequently precipitated in hexane to yield turquoise polymer 34 (146 mg, quant).1H NMR (CDCl3, 300 MHz): δ = 0.80 (d, J = 5.9 Hz, 6 H, 2 CHCH3), 0.93 (d, J = 5.7 Hz, 6 H, 2 CHCH3), 1.09−1.63 (m, 28 H, 14 CH2), 1.94−2.13 (m 4 H, 2 HCCCH2CH2), 2.21−2.59 (m, 6 H, 2 COCH2, 2 CHCH3), 2.61− 2.85 (m, 4 H, 2 HCCCH2), 3.02−3.38 (m, 8 H, 4 CH2N), 3.36 (s, 6 H, 2 OCH3), 3.46−3.55, 3.55−3.65 (2m, 8 H, 2 OCH2CH2O), 3.78− 3.92 (m, 4 H, 2 OCH2CH2N), 4.03 (br, 2 H, 2 NCH), 4.43−4.58 (m, 4 H, 2 OCH2CH2N), 6.89 (br, 2 H, 2 NH), 7.50 (s, 2 H, 2 HCC) ppm; Tg = 7 °C.

Table 1. Ugi Four-Component Test Reactions (Compare Scheme 1) in Different Solvents entry

solvent (0.2 M)

isolated yield of 5 [%]

1 2 3

MeOH THF/MeOH = 1:1 THF

85 69 26

Table 1 shows the isolated yields for the three reactions indicating, as expected, that the Ugi-4CR gives significantly higher yields in methanol than in THF or a mixture of both. Therefore, it seemed to be best to use predominantly methanol for the following polymerizations with only a small amount of the cosolvent. 3.1.2. Monomers for the Ugi-4CR Polymerization. To obtain a polymerization process using the Ugi-4CR, it is necessary to use two bifunctional AA-type components or an AB-type component. AB-type monomers of isocyanide and carboxylic acid or aldehyde and amine would not be feasible, since these would not be stable during storage. Thus, we decided for the AA- and BB-type monomers, where six different combinations are possible (see Scheme 2). In this way, diversely substituted polyamides are generated. As bifunctional AA-type monomers, two dicarboxylic acids, namely sebacic acid 6 and the olefin metathesis derived product icosanedioc acid 7, have been employed. Furthermore, commercially available hexamethylenediamine 8 and 1,12diaminododecane 9 have been used as diamine components. Thereof derived diisocyanides have been synthesized according to literature-known procedures (10 and 11).27,28 Terephthalaldehyde 12 and the olefin metathesis derived C20-dialdehyde 13 have been considered as dialdehyde components. However, these last mentioned monomers did not lead to successful polymerizations. Only dimers or trimers have been formed. In the case of terephthalaldehyde, this might be caused by steric hindrance. A reduced reactivity due to the conjugated system can be ruled out, since benzaldehyde is an excellent component for Ugi-4CRs. In the case of (E)-icos-10-enedial 13, detailed studies revealed that the aldol-condensation product is formed in considerable amounts as a byproduct. As one proof, a test reaction with 10-undecenal 14 and propylamine 15 in methanol at room temperature was carried out (Scheme 3). Under these typical Ugi-4CR conditions, a significant amount (30%) of aldol-condensation product 17 was detected by GC-MS after 13 h reaction time. It is obvious that every side reaction must be avoided, not only for Ugi polymerization reactions, since otherwise undefined and low molecular weight polymers are obtained and the stoichiometry of the reacting groups is altered. Therefore, the aldehyde component must have a blocked αposition, such as in benzaldehyde or isobutyraldehyde, which does not allow (or does not favor) deprotonation due to a lack of or low α-CH-acidity. The later on described dialdehyde component was especially designed for this purpose. Its synthesis is shown in Scheme 4 (for detailed information see Supporting Information). 3.2. Ugi-4CR Polycondensations. 3.2.1. Combination of Diamine and Dicarboxylic Acid. First, we combined hexamethylenediamine 8, sebacic acid 6, isobutyraldehyde 2, and tert-butyl isocyanide 4 in an Ugi polymerization reaction (Scheme 5). Starting with the imine formation and subsequent addition of the remaining components, a typical procedure for

3. RESULTS AND DISCUSSION 3.1. General Considerations. 3.1.1. Choice of the Solvent. Ugi-4CRs are usually performed in methanol as solvent. Having the synthesis of polymers in mind, this solvent seems unsuitable since many polymers precipitate in methanol (as do some of the herein synthesized polymers). Therefore, a solvent mixture is needed benefiting the Ugi reaction and preventing polymer precipitation. For this, THF as cosolvent was tested in a conventional Ugi-4CR observing the effect on the yield. Employing structurally similar starting materials to the later on used monomers, reactions in methanol, THF/ methanol = 1:1 and THF as solvent have been performed (compare Scheme 1 and Table 1). Scheme 1. Ugi Four-Component Test Reaction Using Equimolar Amounts of Hexanoic Acid 1, Isobutyraldehyde 2, n-Butylamine 3, and tert-Butyl Isocyanide 4 as Starting Materials

2777


Macromolecules

Article

Scheme 2. General Representation of All Six Possible Monomer Combinations That Are Polymerizable via the Ugi-4CR (Using Two Bifunctional and Two Monofunctional Monomers); Diversely Substituted Polyamides Are Schematically Depicted

Scheme 3. Test Reaction Showing Side-Product Formation under Typical Ugi-4CR Conditions

1.0 mmol of bifunctional component) in a THF/MeOH 1:2 mixture (see discussion above for choice of solvent). Size exclusion chromatography (SEC) of the resulting reaction mixtures revealed that with higher concentrations, higher molecular weights and better conversions were obtained. However, if the concentration was too high, the obtained molecular weight decreased again, which can be explained by the high viscosity of the reaction mixture and resulting low mobility of polymer chains (compare Figure 1; Table 2, entries 1−5). Further improvement was achieved by employing a 2 equiv excess of the monofunctional components, guaranteeing availability of these reactants even at high conversions (Table 2, entry 6). Interestingly, depending on the dilution, the peak in the chromatogram appearing at 102.7 g/mol (11.8 min.) is more or less pronounced (chromatograms are normalized to this peak). Size exclusion chromatography coupled to electrospray

Scheme 4. Synthesis of Dialdehyde 19 Starting from Ethyl 2Methyl-4-pentenoate 18

Ugi-4CR reactions, it can be ensured that the Passerini-3CR is not occurring. All polymerizations were performed at room temperature since elevated temperature showed less favorable results (lower molecular weights). All reactions were run for at least 36 h. Longer reaction times did not give better results (i.e., higher molecular weights). At first, we studied different polymerizations varying the amount of solvent (1.0−5.0 mL referred to 2778


Macromolecules

Article

Scheme 5. Polymerization of Hexamethylenediamine 8, Sebacic Acid 6, Isobutyraldehyde 2, and tert-Butyl Isocyanide 4

Figure 1. SEC traces of the concentration screening with monomers 2, 4, 6, and 8.

Figure 2. SEC-ESI-MS analysis of the peak at 11.8 min indicating ringclosing reactions during Ugi polymerizations.

Table 2. Results of the Optimization Experiments with Monomers 2, 4, 6, and 8 solvent mixture entry THF/MeOH 1 2 3 4 5 6 7 8 9 10 11

1:2 1:2 1:2 1:2 1:2 1:2 1:1 2:1 3:1 2:1 2:1

solvent [mL] 1.0 1.5 3.0 4.0 5.0 1.5 1.5 1.5 1.5 1.5 1.5

excess of monofunctional components (equiv)

Mn [g/mol] before precipitation

Đ

2.0

2750 4500 3800 2800 2850 5850 6150 7750 2300 8500 5950

1.84 2.77 2.46 2.07 1.93 2.33 2.68 2.84 1.67 2.80 2.42

1.1 1.5

results compared to the corresponding THF/MeOH mixtures. Finally, we added the monofunctional components in small excess and improved thereby the polymer formation. Excess of more than 1.1 equiv did not lead to further improvement (Table 2, entries 10 and 11). Next, the polymer had to be purified by precipitation. Most challenging was the separation of the ring-closing product without losing low molecular weight chains. The best precipitation was achieved in ice-cold diethyl ether obtaining polymer 20 in 67% yield having a Mn of 11 300 g/mol and Đ = 2.35 (Figure 3). In additional polymerizations, instead of hexamethylenediamine 8, 1,12-diaminododecane 9 was used as bifunctional

ionization mass spectrometry (SEC-ESI-MS) revealed that this peak correlates to products resulting from ring-closing reactions (Figure 2). Further improvement of the polymerization was achieved by a variation of the solvent mixture. As expected, there is a certain percentage of each solvent that provides optimal conditions for the polymerization. On the one hand, as shown in the test reactions, methanol improves the conversion of the Ugi-4CR itself; on the other hand, enough THF has to be added to dissolve the polymer properly. We found that a higher amount of THF is benefiting the reaction, especially a 2:1 ratio. However, a 3:1 ratio showed a negative effect on the polymerization (Table 2, entries 7−9). Moreover, we tested if dichloromethane (DCM) or mixtures of DCM and methanol improved the polymerization compared to THF. As expected, pure DCM as solvent did not lead to polymer formation. Mixtures of DCM and MeOH resulted in significantly inferior

Figure 3. SEC traces of the best polymerization conditions (Table 2, entry 10) employing hexamethylenediamine 8, sebacic acid 6, isobutyraldehyde 2, and tert-butyl isocyanide 4 in an Ugi-4CR before and after precipitation. 2779


Macromolecules

Article

components (Table 3, 22). SEC analysis of the precipitated polymer 22 gave a Mn value of 12 450 g/mol (Đ = 2.51). In this case, the yield was rather low (54%) since the polymer had to be precipitated twice in diethyl ether to get rid of the formed rings. In contrast, polymerization with 1,12-diaminododecane as diamine component gave less ring-formation side products, which might be due to the less probable ring closing due to increased monomer size. Here, using the same reaction conditions, a yield of 94% was achieved (Mn = 17 800 g/mol, Đ = 2.23; Table 3, 23). The structure of the polymers was confirmed by 1H NMR spectroscopy, which can be found in the Supporting Information. DSC analysis gave similar results as the polymers obtained from sebacic acid 6 and hexamethylenediamine 8 or 1,12-diaminododecane 9, respectively (see Table 3). 3.2.3. Combination of Diisocyanide and Dicarboxylic Acid. Sebacic acid 6 and 1,6-diisocyanohexane 10 were employed as bifunctional components, while isobutyraldehyde 2 and propylamine 15 were used as monofunctional components (Scheme 7). Since the polymer structure is slightly different compared to 22, having N-alkylated moieties instead of N-acylated ones as side groups, various concentrations (1.1−2.0 mL) and solvent mixtures were tested again. In contrast to the other polymerizations, no influence of the amount of solvent in the range of 1.2−1.8 mL was observed, yet the mixture of the solvents had a crucial effect. The most ideal conditions were found with 1.5 mL of a THF/MeOH 2:1 mixture with 1.5 equiv excess of monofunctional components, leading to a polymer with the average molecular weight of 6700 g/mol (Đ = 2.57) before and 7700 (Đ = 2.38) after precipitation (Table 4, 24). In an additional polymerization, icosanedioic acid 7 was used as bifunctional acid component. Two reactions with different amounts of solvent were performed in a THF/MeOH = 2:1 mixture. Even though both times the icosanedioic acid 7 was barely dissolved, the higher molecular weight was achieved with the lower amount of solvent. Average molecular weights of 5800 g/mol (Đ = 2.24) before and 7150 g/mol (Đ = 2.24) after precipitation in diethyl ether at room temperature were obtained (Table 4, 25). Polymer 24 exhibits a Tg at 42 °C and 25 at 19 °C. 3.2.4. Combination of Dialdehyde and Dicarboxylic Acid. The combination of sebacic acid 6, 2,7-dimethyloctanedial 19, tert-butyl isocyanide 4, and propylamine 15 leads to polyamides having amide side chains (Scheme 8). Such structural motifs have already been synthesized by our group in a two-step procedure.24 In general, the one-pot reactions proceed most efficiently when the dialdehyde component is freshly synthesized prior to use. We observed that a storage of only 3 days already resulted in inferior results. Furthermore, we found that 1.5 mL of a

amine. The best conditions were 2.4 mL of a THF/MeOH 2:1 mixture with 1.2 equiv excess of the monofunctional components, yielding polymer 21 with an Mn of 9300 g/mol (Đ = 2.51) before and Mn of 12 000 g/mol (Đ = 2.21) after precipitation. The successful polymerization was also confirmed by 1H NMR spectroscopy. Very characteristic are the broad singulets at 4.10 and 6.49 ppm corresponding to the CH group b and the amide proton a (Figure 4).

Figure 4. 1H NMR spectrum of Ugi-derived polymer 21.

Finally, the obtained polymers 20 and 21 were investigated by differential scanning calorimetry (DSC). In contrast to conventional polyamides, they do not show a melting transition. This might be due to the bulky side groups and low amount of hydrogen bonding. A glass transition (Tg) was observed in both cases. Polymer 20 shows a Tg at 60 °C and, as expected, polymer 21 a lower one of 39 °C due to the lower frequency of side chains. 3.2.2. Combination of Diamine and Diisocyanide. The combination of diamines and diisocyanides leads to very different polyamide structures having acyl-substituted and nonsubstituted nitrogen atoms. For optimization of this Ugi polymerization strategy, we used hexamethylenediamine 8, 1,6diisocyanohexane 10, isobutyraldehyde 2, and hexanoic acid 1 as components (Scheme 6). The following investigations were analogously performed to the above presented study and will only shortly be summarized. First, solvent mixtures of THF and methanol were tested, whereby an excess of methanol showed the best results. Then, the amount of solvent was varied in the range of 1.0−2.0 mL, which revealed to be the relevant range for the Ugi polymerizations (1.0−0.5 M with respect to the bifunctional component). The highest molecular weights were obtained with 1.7 mL of solvent and 1.5 equiv of monofunctional

Scheme 6. Polymerization of Hexamethylenediamine 8, 1,6-Diisocyanohexane 10, Isobutyraldehyde 2, and Hexanoic Acid 1

2780


Macromolecules

Article

Table 3. Optimized Reaction Conditions and Characterization of the Ugi Polymers 22 + 23 polymer

solvent mixture THF/MeOH

solvent [mL]


Mn [g/mol] after precipitation

Đ

yield [%]

Tg [°C]

22 23

1:2 1:2

1.7 1.7

1.5 1.5

12 450 17 800

2.55 2.23

54 94

65 21

Scheme 7. Polymerization of Sebacic Acid 6, 1,6-Diisocyanohexane 10, Isobutyraldehyde 2, and Propylamine 15



solvent [mL]



Đ

yield [%]

Tg [°C]

24 25

2:1 2:1

1.5 1.5

1.5 1.5

7700 7150

2.38 2.24

75 79

42 19

Scheme 8. Polymerization of Sebacic Acid 6, 2,7-Dimethyloctanedial 19, tert-Butyl Isocyanide 4, and Propylamine 15



solvent [mL]



Đ

yield [%]

Tg [°C]

26 27

1:2 1:2

1.5 1.8

1.1 1.1

14 400 11 800

1.95 1.93

68 72

59 25

Scheme 9. Polymerization of 1,6-Diisocyanohexane 10, 2,7-Dimethyloctanedial 19, Hexanoic Acid 1, and Propylamine 15

Besides, icosanedioic acid 7 was successfully employed in the Ugi polymerization, which required marginally more solvent (Table 5, 27). Yields of about 70% were reached in both cases. 3.2.5. Combination of Diisocyanide and Dialdehyde. 1,6Diisocyanohexane 10 and 2,7-dimethyloctanedial 19 were employed as bifunctional monomers, whereas hexanoic acid 1 and propylamine 15 served as monofunctional components (Scheme 9). The resulting structure of the polyamide is quite different to the ones before. It is highly branched and therefore other properties can be expected.

THF/MeOH 1:2 solvent mixture was most suited for this type of polymerization. Interestingly, this corresponds to our first considerations that methanol benefits the Ugi-4CR, but generally, we could not see any tendency that would allow us to predict which monomer combination prefers which solvent mixture. A quick optimization is thus necessary for every new monomer combination. Further improvement was achieved by a small excess of amine and isocyanide component. More than 1.1 equiv of these reagents led to lower molecular weights. Finally, a Mn value of 14 400 g/mol was determined having typical dispersity for step-growth process (Table 5, 26). 2781


Macromolecules

Article



solvent [mL]



Đ

yield [%]

Tg [°C]

28 29

1:1 1:1

1.5 1.5

2.0 2.0

9950 10750

2.27 2.30

74 88

23 1

Scheme 10. Polymerization of 1,6-Hexamethylenediamine 8, 2,7-Dimethyloctanedial 19, Hexanoic Acid 1, and tert-Butyl Isocyanide 4


solvent mixture THF/ MeOH

solvent [mL]



Đ

yield [%]

Tg [°C]

30 31

2:1 2:1

1.5 1.5

1.1 1.1

10 650 12 750

2.08 2.22

62 90

43 25

The typical optimization screening revealed that 1.5 mL of a THF/MeOH 1:1 mixture provides the optimal reaction medium. Furthermore, high excess of monofunctional components showed superior results; an excess of 2 equiv was employed. In this way, a polymer of Mn = 9950 g/mol (Đ = 2.27) was obtained in 74% yield (Table 6, 28). In the same manner, the longer-chained 1,12-diisocyanododecane 11 was used, which resulted in a similar average molecular weight, but higher yield of 88% (Table 6, 29). This is caused by the required 2-fold precipitation of polymer 28. DSC analysis of 28 and 29 clearly show lower glass transitions compared to the corresponding polymers of the other polymerizations. 3.2.6. Combination of Dialdehyde and Diamine. The final combination of 1,6-hexamethylenediamine 8, 2,7-dimethyloctanedial 19, hexanoic acid 1, and tert-butyl isocyanide 4 gives polymers with amides only in the side chain (Scheme 10). Here, for the first the time, the initial imine formation already results in polymers, namely polyimines. These are known to precipitate in methanol. Therefore, the imine was preformed in THF instead of methanol, and subsequently, the isocyanide and carboxylic acid were added. In this way, well-soluble polymers are formed, and afterward, methanol is added promoting further Ugi reactions. Thus, a solvent mixture with higher amount of THF was more efficient. Good improvement was also achieved employing a slight excess of monofunctional components (1.1 equiv). Higher amounts worsened the polymerization process. Both polymers (30 and 31), employing 1,6-hexamethylenediamine or 1,12-diaminododecane, respectively, exhibit molecular weights over 10 kDa and glass transitions at 43 and 25 °C, respectively (Table 7). While polymer 31 was obtained in high yield, 30 was obtained in 62% yield due to required 2-fold precipitation. 3.3. Introduction of Functional Groups. The Ugi-4CR polymerization approach offers manifold opportunities to introduce functional groups under very mild reaction conditions. As one possible example, we used the optimized reaction conditions of polymer synthesis 22 and replaced

hexanoic acid 1 with 5-hexynoic acid 35. This resulted in polyamide 32 (Mn = 21 400 g/mol, Đ = 2.33) with terminal alkynes in its side chains, which provide many post-polymerization modification possibilities, such as thiol−yne and azide− alkyne chemistry. As representative example, we grafted 1azido-2-(2-methoxyethoxy)ethane 33 onto the alkyne-functionalized polymer 32, resulting in polyamide 34. The successful coupling was evidenced by SEC and 1H NMR analysis (Figure 5). While the SEC chromatogram hardly shows shifting, the NMR signal of the terminal alkyne disappears and new signals according to the diethylene glycol methyl ether appear. In this

Figure 5. 1H NMR spectra of polymer 32 and 34 with assigned signals and corresponding GPC. 2782


Macromolecules

Article

(16) Passerini, M. Gazz. Chem. Ital. 1921, 51, 126−129. (17) Deng, X.-X.; Li, L.; Li, Z.-L.; Lv, A.; Du, F.-S.; Li, Z.-C. ACS Macro Lett. 2012, 1 (11), 1300−1303. (18) Zhang, L.-J.; Deng, X.-X.; Du, F.-S.; Li, Z.-C. Macromolecules 2013, 46 (24), 9554−9562. (19) Sehlinger, A.; Schneider, R.; Meier, M. A. R. Eur. Polym. J. 2014, 50 (0), 150−157. (20) Chan, C. Y. K.; Tseng, N.-W.; Lam, J. W. Y.; Liu, J.; Kwok, R. T. K.; Tang, B. Z. Macromolecules 2013, 46 (9), 3246−3256. (21) Lee, I.-H.; Kim, H.; Choi, T.-L. J. Am. Chem. Soc. 2013, 135 (10), 3760−3763. (22) Siamaki, A. R.; Sakalauskas, M.; Arndtsen, B. A. Angew. Chem., Int. Ed. 2011, 50 (29), 6552−6556. (23) Bu, H.; Kjøniksen, A.-L.; Knudsen, K. D.; Nyström, B. Biomacromolecules 2004, 5 (4), 1470−1479. (24) Kreye, O.; Türünç, O.; Sehlinger, A.; Rackwitz, J.; Meier, M. A. R. Chem.Eur. J. 2012, 18 (18), 5767−5776. (25) Robotham, C.; Baker, C.; Cuevas, B.; Abboud, K.; Wright, D. Mol. Diversity 2003, 6 (3−4), 237−244. (26) Yang, B.; Zhao, Y.; Fu, C.; Zhu, C.; Zhang, Y.; Wang, S.; Wei, Y.; Tao, L. Polym. Chem. 2014, in press. (27) Obrecht, R.; Herrmann, R.; Ugi, I. Synthesis 1985, 1985 (04), 400−402. (28) Ugi, I.; Fetzer, U.; Eholzer, U.; Knupfer, H.; Offermann, K. Angew. Chem., Int. Ed. Engl. 1965, 4 (6), 472−484.

manner, the introduction of many other functional groups should be feasible.

4. CONCLUSIONS The Ugi-4CR was introduced as valuable tool for the synthesis of polyamides of various structures. The nature of multicomponent reactions makes this approach highly atomeconomic and gives the possibility of modular design. In this way, six generally different polyamide types have been synthesized under very mild reaction conditions and without the use of any catalyst. Furthermore, renewable building blocks have been incorporated, and due to the polycondensation process, only water is expelled as side product. The obtained polymers mainly reached molecular weights above 10 kDa and showed only glass transitions. Moreover, a facile introduction of functional groups was shown, which provides the possibility for post-polymerization modifications. Here, a grafting via azide− alkyne cycloaddition was demonstrated.

■

ASSOCIATED CONTENT

S Supporting Information *

Monomers and azide synthesis including 1H and 13C NMR spectra, Ugi-4CR test reactions, NMR spectra of polymers 20− 31. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (M.A.R.M.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors are thankful to Nikolai Bartnick for experimental support. We are also thankful to Christopher Barner-Kowollik and his group at KIT for access to the SEC-ESI equipment. A.S. kindly acknowledges a scholarship from the Carl-Zeiss-Stiftung.

■

REFERENCES

(1) Smith, J. K.; Hounshell, D. A. Science 1985, 229 (4712), 436− 442. (2) Genas, M. Angew. Chem. 1962, 74 (15), 535−540. (3) Hanford, W. E.; Joyce, R. M. J. Polym. Sci. 1948, 3 (2), 167−172. (4) Griehl, W.; Ruestem, D. Ind. Eng. Chem. 1970, 62 (3), 16−22. (5) Braun, E.; Levin, B. C. Fire Mater. 1987, 11 (2), 71−88. (6) Biggs, B. S.; Frosch, C. J.; Erickson, R. H. Ind. Eng. Chem. 1946, 38 (10), 1016−1019. (7) Marks, B. S.; Schweiker, G. C. J. Polym. Sci. 1960, 43 (141), 229− 239. (8) Saotome, K.; Komoto, H. J. Polym. Sci., Part A-1: Polym. Chem. 1967, 5 (1), 107−117. (9) Wittbecker, E. L.; Houtz, R. C.; Watkins, W. W. Ind. Eng. Chem. 1948, 40 (5), 875−879. (10) Billiet, L.; Hillewaere, X. K. D.; Du Prez, F. E. Eur. Polym. J. 2012, 48 (12), 2085−2096. (11) Ugi, I.; Steinbrückner, C. Angew. Chem. 1960, 72 (7−8), 267− 268. (12) Rudick, J. G. J. Polym. Sci., Part A: Polym. Chem. 2013, 51 (19), 3985−3991. (13) Kakuchi, R. Angew. Chem., Int. Ed. 2014, 53 (1), 46−48. (14) Kreye, O.; Tóth, T.; Meier, M. A. R. J. Am. Chem. Soc. 2011, 133 (6), 1790−1792. (15) Wang, Y.-Z.; Deng, X.-X.; Li, L.; Li, Z.-L.; Du, F.-S.; Li, Z.-C. Polym. Chem. 2013, 4 (3), 444−448. 2783


Diversely Substituted Polyamides: Macromolecular Design Using the

Recommend Documents