Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2022 Oct 17;55(21):9690–9696. doi: 10.1021/acs.macromol.2c01457

Isocyanate-Free Polyurea Synthesis via Ru-Catalyzed Carbene Insertion into the N–H Bonds of Urea

Felix J de Zwart †, Petrus C M Laan †, Nicole S van Leeuwen †, Eduard O Bobylev †, Erika R Amstalden van Hove ‡, Simon Mathew †, Ning Yan †, Jitte Flapper §, Keimpe J van den Berg ∥, Joost N H Reek †, Bas de Bruin †,*
PMCID: PMC9648342  PMID: 36397938

Abstract

graphic file with name ma2c01457_0008.jpg

Polyureas have widespread applications due to their unique material properties. Because of the toxicity of isocyanates, sustainable isocyanate-free routes to prepare polyureas are a field of active research. Current routes to isocyanate-free polyureas focus on constructing the urea moiety in the final polymerizing step. In this study we present a new isocyanate-free method to produce polyureas by Ru-catalyzed carbene insertion into the N–H bonds of urea itself in combination with a series of bis-diazo compounds as carbene precursors. The mechanism was investigated by kinetics and DFT studies, revealing the rate-determining step to be nucleophilic attack on a Ru–carbene moiety by urea. This study paves the way to use transition-metal-catalyzed reactions in alternative routes to polyureas.

1. Introduction

Polyurea-based elastomers find widespread applications in foams and coatings due to their unique material properties, such as tensile strength and tear resistance.1 Routes toward isocyanate-free polyureas and polyurethanes which make use of more benign monomers are of interest due to the toxicity of isocyanates and difficulties in handling these reactive and humidity-sensitive reagents.2,3 The currently available isocyanate-free routes toward polyureas and polyurethanes can be divided into four broad categories, shown in Scheme 1.4−6 In rearrangement pathways (Scheme 1a) isocyanates are formed in situ through Curtius (depicted), Hoffman, or Lossen rearrangements.7 In polycondensation, amines are prefunctionalized with either phosgene or another carbonyl source to furnish a blocked isocyanate, which can then react with an amine or alcohol to yield the desired polyurea (Scheme 1b). Ring-opening pathways use cyclic carbamates or ureas that are then polymerized through transcarbamoylation under high temperatures (Scheme 1c). Polyaddition pathways use cyclic carbonates as precursors for polyurethanes, which can be aminolyzed to polyureas using excess amine (Scheme 1d).8−11 Most of these isocyanate-free routes have their drawbacks; for example, in the formation of isocyanates in situ (Scheme 1a), acyl azides are used as precursors which are also harmful substances. The polycondensation route (Scheme 1b) releases side products during curing which limits industrial usage, which in the case of ring-opening is limited by the high temperatures required (Scheme 1c). The most promising route currently utilizes amines and carbonates (Scheme 1d) as precursors with low toxicity.12,13

Scheme 1. Isocyanate-Free Synthetic Approaches to Polyurethanes (X = O) and Polyureas (X = NH).

Scheme 1

Open in a new tab

Interestingly, the use of (transition-metal) catalysis to arrive at polyurea and polyurethane structures has not been developed as much. Transition-metal-catalyzed polymerizations using diazo compounds provide a powerful alternative synthetic tool to otherwise difficult to access structures. For example, a variety of diazo compounds can be used as monomers in single-component polymerization, leading to highly functionalized polymers.14,15 Polyesters and polyethers can be synthesized from their respective alcohols and acids in a copolymerization reaction with diazo compounds through O–H insertion reactions.16−18 Using amines as precursor, a recent article by Ihara and co-workers has reported on the synthesis of polyamines through ruthenium-catalyzed N–H insertion, a continuation of the research on the synthetic utility of C–N bond formation using diazo compounds.19−24 Ureas have been used as nucleophiles in transition-metal catalysis such as Pd-catalyzed carboaminations and more recently as nitrene precursors in Ru-catalyzed C–H amination.25−28 On the basis of this rationale, we wondered if it would be possible to use N–H insertions to synthesize polyureas as shown below (Scheme 1e). Whereas in all the known approaches (Scheme 1a–d) the urea moiety is constructed in the final step, this approach differs fundamentally with urea itself operating as a nucleophile to react with a ruthenium-centered carbene. Furthermore, with the tunability of diazo precursors a variety of pendant side groups can be attached to influence the material properties of polymers. In this proof-of-concept study we present a new strategy to prepare polyureas by utilizing Ru-catalyzed N–H insertions on urea.

2. Results and Discussion

2.1. Bisfunctional Diazo Compound Synthesis

The bisfunctional diazo compound diethyl 1,4-phenylenebis(diazoacetate), 2a, has been described in the literature recently, and we decided to expand on the scope of phenylenebis(diazoacetate) compounds by changing the ester substituents.29 These donor–acceptor type diazo compounds were specifically chosen because carbene dimerization is known to be greatly suppressed when compared to other diazo compounds.30 With phenylenediacetic acid as a starting substrate, five different bisfunctional diazo compounds were synthesized in a two-step procedure. The esters are readily synthesized under Dean–Stark conditions in toluene with catalytic amounts of sulfuric acid. The active methylene carbon can be functionalized with a diazo moiety through a Regitz diazo transfer using p-acetamidobenzenesulfonyl azide (p-ABSA) as a diazo transfer reagent; products 2a–e were obtained in fair to moderate yields (62–36%) as pure compounds after column chromatography (Scheme 2). The diazo compounds were characterized by 1H and 13C NMR and HR–MS (see the Supporting Information). Compared to the more often used tosyl azide, p-ABSA has the advantage of being less explosive and impact sensitive and is therefore a safer preferred alternative.31

Scheme 2. Synthesis of Bis-Diazo Compounds 2a–e (Yield after Column Chromatography in Parentheses).

Scheme 2

Open in a new tab

2.2. Polymerization

After a successful test reaction using urea and ethyl diazo(phenyl)acetate which provided the desired product (molecular structure determined by X-ray diffraction shown in Figure S1, we focused on optimization of the polymerization reaction. The initial exploration of polymerization conditions was started by polycondensation of 2b with urea in the presence of dichloro(p-cymene)ruthenium(II) dimer. This provided a polymeric material, which could be separated from the reaction mixture by precipitation from diethyl ether. The polymer was analyzed by SEC, which revealed a weight-averaged molecular weight (Mw) of 7.1 kDa. Increasing the ruthenium catalyst loading led to a higher yield (entry 2, Table 1), while increasing the diazo stoichiometry resulted in a lower yield (entries 3–5, Table 1). These two observations point to a step-growth polymerization process. Decreasing the reaction temperature or changing the concentration also led to a lower yield or molecular weight (entries 6–8, Table 1). With the optimized polymerization conditions at hand, the scope of the reaction was explored by changing the diazo substituent (Table 2), where diazos 2a–e were used to synthesize polymers 3a–e. As a solvent for precipitation, hexane was used instead of diethyl ether, as diethyl ether was polar enough to dissolve polymers 3c, 3d, and 3e. This provided polymeric materials in good to moderate (65–45%) yields. The slight differences in obtained yields are presumably a result of the precipitation procedure, as the more soluble sec-butyl-substituted polymer 3c provided the lowest yield. The acquired polymers are soluble in solvents such as DCM, chloroform, and dimethyl sulfoxide and poorly soluble in hexane and methanol and insoluble in water. Through size exclusion chromatography (SEC) analysis based on linear polystyrene standards, weight-average molar masses (Mw) and dispersities (Đ) of the produced polyureas were estimated to be in the ranges of 3.9–7.1 kDa and 1.3–1.6, respectively (Table 2). We then continued to use polymer 3a as a starting point for polymer characterization.

Table 1. Polycondensation of 2b with Ureaa.

2.2.

No. Deviations Yieldb (%) Mw (kDa)c Đc
1 none 65 7.1 1.50
2 10 mol % Ru 94 6.3 1.61
3 1.1 equiv diazo 55 5.3 1.53
4 1.2 equiv diazo 25 6.1 1.57
5 1.3 equiv diazo 0    
6 0 °C 22 2.8 1.38
7 25 mL DCM 30 7.4 1.58
8 1 mL DCM 77 3.6 1.24
Open in a new tab
a

Conditions: urea (100 μmol), 2b (100 μmol), dichloro(p-cymene)ruthenium(II) dimer (2.5 μmol), DCM (2.5 mL), room temperature, 1 h.

b

Determined by gravimetry after precipitation.

c

Mw/Mn as determined by SEC in DCM.

Table 2. Polycondensation of Urea with Different Bisfunctional Compoundsa.

Polymer Yield (%)b Mw (kDa)c DOP (SEC)c Đc Tg (°C)d
3a 56 4.9 16.2 1.5 141
3b 65 7.1 18.6 1.6 97
3c 45 4.0 13.1 1.4 131
3d 57 4.3 9.6 1.3 82
3e 54 3.9 11.0 1.5 89
Open in a new tab
a

Conditions: urea (100 μmol), diazo 2a–e (100 μmol), dichloro(p-cymene)ruthenium(II) dimer (2.5 μmol), DCM (2.5 mL), room temperature, 1 h.

b

Determined by gravimetry after precipitation.

c

Determined by SEC in DCM.

d

Determined by DSC.

2.3. Characterization

The FT–IR spectrum (Figure 2) of polyurea 3a reveals bands located at 3367, 2981, 1732, and 1643 cm–1, which are related to urea N–H, aromatic C–H, ester C=O, and urea C=O stretching vibrations, respectively. These bands support the incorporation of both functional groups in the polymer chain, and the disappearance of the diazo stretch vibration of the starting material shows full conversion of the bis-diazo compound. The 1H NMR spectrum in DMSO-d6 at 80 °C (Figure 1) shows characteristic signals for the ethyl chain introduced with comonomer 2a at 1.11 and 4.10 ppm (Hd and Hc) and the aromatic protons at 7.35 ppm (He). Two new signals at 6.98 and 5.29 ppm are allocated to the urea Ha and benzylic Hb protons. This assignment was confirmed by 15N-labeling of the urea prior to catalysis, providing a 15N-labeled polymer 3a. The acquired 1H–15N HSQC displays a negative cross-peak, indicative of a secondary amine, between Ha and a doublet in 15N NMR at 89 ppm with a coupling of 91 Hz, supporting the assignment of Ha as the urea N–H proton (inset of Figure 1; see also Figures S51 and S52). To confirm the anticipated polymer structure containing alternating urea and phenylene–diester repeating units, 13C NMR analysis was performed, revealing both the ester and urea carbons at 170 and 156 ppm, respectively (Figure S50). The 13C NMR signals belonging to the aromatic ring were located at 137 and 127 ppm. The carbons of the ethyl chain resonate at 60 and 13 ppm, and the benzylic carbon reveals a signal at 56 ppm. The NMR interpretation of polymers 3b–3e is similar to that of 3a and in accordance with the proposed structure. When using chiral diazo 3c, the benzylic carbon is observed as two signals of equal intensity at 57.3 ppm. This indicates that chiral secondary structures of the resulting polyureas could be accessible when using chiral catalysts capable of enantioselective N–H insertion.

Figure 2.

Figure 2

Open in a new tab

Operando FT–IR monitoring of ruthenium-catalyzed polymerization of 2a and urea. One trace corresponds to 15 s.

Figure 1.

Figure 1

Open in a new tab

1H NMR spectra of 2a (∗: solvent). Inset: 1H–15N HSQC using 15N-labeled urea.

2.4. End-Group Analysis by Mass Spectrometry

To further understand the chemical structure of the polymers, the end groups were studied by mass spectrometry. The relatively low molecular weights obtained for these polyureas could possibility arise from cyclization of the polymers. Indeed, when polymer 3b was subjected to ESI–MS analysis, we observed only signals corresponding to oligomers without end groups (see Figures S24–S30). The absence of end groups strongly indicates the presence of cyclic structures in the polymer.32 Polymers 3a, 3b, and 3e were further studied by MALDI–ToF–MS, which also provided signals in accordance with polymers without an end group (Figures S31–S33). While the data point to formation of mainly cyclic polymers, we cannot fully exclude that some of the higher molecular weight chains (n > 8) could be partially linear though (in MALDI–ToF–MS for n > 8 solvent/water and multiple Na+ adduct formation leads to broad, overlapping peaks which complicates chain-end assignment). Formation of mainly cyclic polymers explains the relatively low molecular weights obtained for the polymers in this study, as cyclization is an effective termination pathway (see Scheme S1).

2.5. Material Properties

To investigate the effect of the ester substituent on the material properties, the glass transition temperature (Tg) was measured. Incorporation of soft segments within polyurea segments is known to lead to a decrease in glass transition temperature.33,34 Indeed, the heptyl-substituted polymer 3d has the lowest Tg and ethyl-substituted diazo 3a has the highest Tg (Table 2). Furthermore, 1,3-phenylene-substituted polymer 3e is observed to have an intermediate Tg of 89 °C while having the same molecular formula as 3a, showing that main-chain connectivity can be used as an effective tool to control the material properties.

2.6. Kinetics

To obtain more insight into the mechanism of polymerization, the polycondensation of 2a with urea was followed by operando IR spectroscopy, as shown in Figure 2. A clear decrease in the signal at 2091 cm–1, corresponding to the disappearance of the diazo moiety, of the monomer was observed. Furthermore, a new signal corresponding to the C=O stretch vibration of the polymer is observed at 1734 cm–1. Using these two signals the conversion and yield over time was monitored to provide insight into the kinetics of this reaction. When using 1,3-substituted diazo 2e, the conversion decreased linearly over time, indicating zeroth order in diazo monomer concentration (Figure S7). On the other hand, with 1,4-substituted diazo 2a some rate dependence on conversion was observed. To investigate this further with improved time resolution, kinetic experiments were undertaken to derive the rate law for both diazo 2a and 2e by monitoring the gas production of the reaction with a bubble counter.35 For diazo 2a, the diazo order dependence in the range of 5–10% catalyst loading was found to not clearly fit to a reaction order (Figures S16–S21). We believe this to be an effect of the para substitution on the diazo, causing the electronics of one diazo moiety to be influenced by reactions at the other, thereby complicating the reaction profile. Therefore, the rest of the kinetics were undertaken using meta-substituted diazo 2e, for which the catalytic profile is more clear. As such, for diazo 2e a first-order rate dependence in catalyst concentration was found in the range of 5–10% catalyst loading, excluding any multinuclear pathways (Figures S8–S10). For diazo 2e a zeroth-order dependence of rate upon diazo concentration was found (Figures S11–S13). The low solubility (0.2 mg/mL, see the Supporting Information for details) of urea in dichloromethane prevents us from determining the order in urea. The zeroth-order kinetic in diazo 2e suggests that diazo activation is fast, and presumably the follow-up reaction with urea is the rate-limiting step. This contrasts with previous work on rhodium X–H insertions, for which carbene formation was shown to be rate-limiting.36 The kinetics in this case should (at least in part) be influenced by the low solubility of urea, which causes the concentration of urea to remain low and constant throughout. Transition-metal-catalyzed X–H insertions are generally understood to proceed via a four-step mechanism (Scheme 3a, vide infra), consisting of (A) diazo coordination, (B) carbene formation, (C) nucleophilic attack, and (D) proton shift.37,38 Having excluded A and B as rate determining, kinetic isotope effect studies were undertaken using d4-urea and diazo 2e. Using the initial rates until 20% conversion the kinetic isotope effect (KIE) for urea was found to be kH/kD = 1.31 (Figures S14 and S15), corresponding to a secondary kinetic isotope effect.39 This KIE strongly indicates the rate-determining step to be nucleophilic attack, as step C involves rehybridization of the urea nitrogen for which a larger KIE would be expected. This result is different from known copper and rhodium systems,37 for which fast (non-rate-limiting) nucleophilic attack of amines and alcohols to the carbene was observed. The low solubility and poor nucleophilicity of urea explain why nucleophilic attack is rat-determining in this case.

Scheme 3. (a) Catalytic Cycle for Ruthenium Catalyzed Carbene N–H Insertion: (A) Diazo Coordination, (B) Carbene Formation, (C) Nucleophilic Attack, and (D) Proton Shift; (b) Transition State Structure for Nucleophilic Attack by Urea (CPK Coloring).

Scheme 3

Open in a new tab

2.7. Density Functional Theory

To further investigate the catalytic mechanism, we pursued DFT calculations to shed light on the nature of the kinetic isotope effect (gas phase, BP86, def2-TZVP, D3). As previous experiments indicated no involvement of the diazo compound in the rate-determining step, we first investigated steps A and B to confirm this. As chlorido ligands are known to be displaced from similar ruthenium arene species by carboxamide donors, an intramolecular mechanism in which urea first coordinates to ruthenium (via its carbonyl group) was investigated (Scheme 3b).40 Coordination of phenyl-2-diazoacetate to the starting complex (step A, Scheme 3a) was found to be downhill by −2.3 kcal mol–1. Then, release of dinitrogen from the diazo adduct to form the ruthenium carbene was found to have a small barrier of 6 kcal mol–1 (step B, Scheme 3a). This step is strongly exergonic, and release of dinitrogen was found to be downhill by −39.0 kcal mol–1. The barrier ΔG‡ for nucleophilic attack from urea on the carbene (step C, Scheme 3a) was found to be 11.53 kcal mol–1, in accordance with the experimentally observed fast reaction at room temperature.

Interestingly, a slight dependence of the transition state energy on the orientation of the carbene was found if the aryl moiety is pointing toward the urea the barrier was slightly increased to 12.3 kcal mol–1. By visualizing the displacement vectors, a N–H bending vibration can be observed in the intrinsic reaction coordinate of the transition state (Scheme 3b), pointing toward a secondary kinetic isotope effect for deuteration of this position. Furthermore, by recalculating the vibrational correction to the Gibbs free energy of the starting material and the transition state, a DFT estimate of the kinetic isotope effect can be calculated. The transition state barrier for d4-urea ΔΔG‡ was found to be 11.67 kcal mol–1 corresponding to kH/kD = 1.27, in accordance with the experimentally derived value. The DFT results therefore support nucleophilic attack to be rate-determining for the ruthenium-catalyzed copolymerization of urea and bis-diazos. The subsequent proton transfer through a 1,5-proton shift toward the ester moiety was calculated to have a DFT barrier of 13.5 kcal mol–1; however, as this is presumably substrate or solvent assisted, the experimental barrier in solution is expected to be lower.

2.8. Copolymerization

Commercial polyureas get their unique properties from having a mixture of soft and hard segments within their polymer backbone.41 This is generally achieved by mixing different polyamines with isocyanates, and as such we were interested in whether the developed Ru-catalyzed polycondensation was suitable for copolymerization. To incorporate a soft segment, a poly(tetramethylene oxide) (PTMO) oligomer (Mn = 1000 g/mol) was end-capped with phenyldiazoacetate units in a two-step procedure.

First, phenylacetyl chloride was used to introduce phenylacetyl groups after a similar Regitz diazo transfer procedure was used to introduce diazo groups on the end, providing telechelic polymer 2f (Mn = 1500 g/mol, determined by SEC). When reacted with urea under the optimized polycondensation conditions as described above (Table 3, entry 3f), a polymer with a molecular weight of 8.3 kDa was obtained indicating successful copolymerization, with a Tg observed at 34 °C (Figure S23). To incorporate more hard blocks within the polymer, copolymerization with diazo 2a was performed. When telechelic polymer 2f was copolymerized with 2a, a material with molecular weight 12.2 kDa and a glass transition temperature of 39 °C was obtained (Table 3, entry 3g). NMR integration of 3g indicates that the ratio of incorporation is consistent with the feed ratio (Figure S67). Furthermore, the molecular weight distributions obtained from SEC in all cases displayed monomodal distributions (Figure S23), showing the efficacy to use multiple diazo compounds in copolymerization. Further studies are directed at further tuning the material properties to not only emulate the molecular structure of polyureas but also gain the desirable features present in commercial polyureas.

Table 3. Copolymerization of an End-Group Functionalized Poly(tetramethylene oxide) (PTMO), Diazo 2a, and Ureaa.

2.8.

Polymer 2a (mmol) 2f (mmol) Urea (mmol) Mw (kDa)b Đb Tgc
3a 100 0 100 4.9 1.54 141
3f 0 100 100 8.3 2.1 34
3g 100 100 200 12.2 2.09 39
Open in a new tab
a

Conditions: urea (100 μmol), 2b (100 μmol), dichloro(p-cymene)ruthenium(II) dimer (2.5 μmol), DCM (2.5 mL), room temperature, 1 h.

b

Determined by SEC in DCM.

c

Determined by DSC.

3. Conclusion

In this work, we have demonstrated the capability to synthesize polyureas by ruthenium-catalyzed N–H insertion reactions, wherein urea uniquely functions as a nucleophile. With this protocol, polyurea moieties are accessible through a route completely free of isocyanate. The formed polymers were found to have material properties tunable through side-chain or main-chain substitution. The mechanistic investigations show nucleophilic attack of urea on the formed carbene to be rate-determining. This work shows the possibility of using diazo compounds in combination with transition-metal catalysis to furnish novel routes toward isocyanate-free polyureas.

Acknowledgments

Financial support from the Advanced Research Center for Chemical Building Blocks (ARC CBBC, project 2018.015.C and 2019.021.A), which is cofounded and cofinanced by the Dutch Research Council (NWO) and The Netherlands Ministry of Economic Affairs and Climate Policy, is gratefully acknowledged. P.C.M.L. and N.Y. acknowledge the financial support from The Netherlands Organization for Scientific Research (NWO) VIDI program (VI.Vidi.192.045).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.macromol.2c01457.

  • Synthetic procedures; NMR characterization of compounds and polymers; kinetics data; DSC profiles; MS analysis of polymers; DFT details and coordinates of all stationary points (PDF)

  • Crystallographic details for 5 (CIF)

The authors declare no competing financial interest.

Supplementary Material

ma2c01457_si_002.pdf (4MB, pdf)
ma2c01457_si_001.cif (2.5MB, cif)

References

  1. Howarth G. Polyurethanes, Polyurethane Dispersions and Polyureas: Past, Present and Future. Surface Coatings International Part B: Coatings Transactions 2003, 86 (2), 111–118. 10.1007/BF02699621. [DOI] [Google Scholar]
  2. Yakeya D.; Yoshida Y.; Endo T. Phosgene-Free and Chemoselective Synthesis of Novel Polyureas from Activated l -Lysine with Diphenyl Carbonate. Macromolecules 2020, 53 (16), 6809–6815. 10.1021/acs.macromol.0c01039. [DOI] [Google Scholar]
  3. White B. T.; Migliore J. M.; Mapesa E. U.; Wolfgang J. D.; Sangoro J.; Long T. E. Isocyanate- And Solvent-Free Synthesis of Melt Processible Polyurea Elastomers Derived from Urea as a Monomer. RSC Adv. 2020, 10 (32), 18760–18768. 10.1039/D0RA02369H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Cornille A.; Auvergne R.; Figovsky O.; Boutevin B.; Caillol S. A Perspective Approach to Sustainable Routes for Non-Isocyanate Polyurethanes. Eur. Polym. J. 2017, 87, 535–552. 10.1016/j.eurpolymj.2016.11.027. [DOI] [Google Scholar]
  5. Zhou X.; Li Y.; Fang C.; Li S.; Cheng Y.; Lei W.; Meng X. Recent Advances in Synthesis of Waterborne Polyurethane and Their Application in Water-Based Ink: A Review. Journal of Materials Science and Technology 2015, 31 (7), 708–722. 10.1016/j.jmst.2015.03.002. [DOI] [Google Scholar]
  6. Carré C.; Ecochard Y.; Caillol S.; Avérous L. From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes. ChemSusChem 2019, 12, 3410–3430. 10.1002/cssc.201900737. [DOI] [PubMed] [Google Scholar]
  7. Filippi L.; Meier M. A. R. Fully Renewable Non-Isocyanate Polyurethanes via the Lossen Rearrangement. Macromol. Rapid Commun. 2021, 42 (3), 2000440. 10.1002/marc.202000440. [DOI] [PubMed] [Google Scholar]
  8. He X.; Xu X.; Wan Q.; Bo G.; Yan Y. Solvent- and Catalyst-Free Synthesis, Hybridization and Characterization of Biobased Nonisocyanate Polyurethane (NIPU). Polymers (Basel) 2019, 11 (6), 1026. 10.3390/polym11061026. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Wu Z.; Tang L.; Dai J.; Qu J. Synthesis and Properties of Fluorinated Non-Isocyanate Polyurethanes Coatings with Good Hydrophobic and Oleophobic Properties. J. Coat. Technol. Res. 2019, 16 (5), 1233–1241. 10.1007/s11998-019-00195-5. [DOI] [Google Scholar]
  10. Bossion A.; Aguirresarobe R. H.; Irusta L.; Taton E.; Cramail H.; Grau D.; Mecerreyes E.; Su A. J.; Liu G.; Müller G.; Sardon H. . Unexpected Synthesis of Segmented Poly(Hydroxyurea-Urethane)s from Dicyclic Carbonates and Diamines by Organocatalysis. Macromolecules 2018, 51 (15), 5556–5566. 10.1021/acs.macromol.8b00731. [DOI] [Google Scholar]
  11. Ma S.; Liu C.; Sablong R. J.; Noordover B. A. J.; Hensen E. J. M.; van Benthem R. A. T. M.; Koning C. E. Catalysts for Isocyanate-Free Polyurea Synthesis: Mechanism and Application. ACS Catal. 2016, 6 (10), 6883–6891. 10.1021/acscatal.6b01673. [DOI] [Google Scholar]
  12. Wołosz D.; Parzuchowski P. G.; Rolińska R. J. Environmentally Friendly Synthesis of Urea-Free Poly(Carbonate-Urethane) Elastomers. Macromolecules 2022, 55 (12), 4995–5008. 10.1021/acs.macromol.2c00706.. [DOI] [Google Scholar]
  13. Besse V.; Camara F.; Méchin F.; Fleury J. P.; Caillol S.; Pascault F.; Boutevin B. How to Explain Low Molar Masses in PolyHydroxyUrethanes (PHUs). Eur. Polym. J. 2015, 71, 1–11. 10.1016/j.eurpolymj.2015.07.020.. [DOI] [Google Scholar]
  14. Jellema E.; Jongerius A. L.; Reek J. N. H.; de Bruin B. C1 Polymerisation and Related C-C Bond Forming ‘Carbene Insertion’ Reactions. Chem. Soc. Rev. 2010, 39 (5), 1706–1723. 10.1039/B911333A. [DOI] [PubMed] [Google Scholar]
  15. Shimomoto H.; Moriya T. A.; Mori T.; Itoh T.; Kanehashi S.; Ogino K.; Ihara E. Single-Component Polycondensation of Bis(Alkoxycarbonyldiazomethyl)Aromatic Compounds to Afford Poly(Arylene Vinylene)s with an Alkoxycarbonyl Group on Each Vinylene Carbon Atom. ACS Omega 2020, 5 (10), 4787–4797. 10.1021/acsomega.9b03408. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Shimomoto H.; Itoh E.; Itoh T.; Ihara E.; Hoshikawa N.; Hasegawa N. Polymerization of Hydroxy-Containing Diazoacetates: Synthesis of Hydroxy-Containing “Poly(Substituted Methylene)s” by Palladium-Mediated Polymerization and Poly(Ester-Ether)s by Polycondensation through O-H Insertion Reaction. Macromolecules 2014, 47 (13), 4169–4177. 10.1021/ma500783b. [DOI] [Google Scholar]
  17. Shimomoto H.; Mori T.; Itoh T.; Ihara E. Poly(β-Keto Enol Ether) Prepared by Three-Component Polycondensation of Bis(Diazoketone), Bis(1,3-Diketone), and Tetrahydrofuran: Mild Acid-Degradable Polymers to Afford Well-Defined Low Molecular Weight Components. Macromolecules 2019, 52 (15), 5761–5768. 10.1021/acs.macromol.9b00653. [DOI] [Google Scholar]
  18. Wang X.; Ding Y.; Tao Y.; Wang Z.; Wang Z.; Yan J. Polycondensation of Bis(α-Diazo-1,3-Dicarbonyl) Compounds with Dicarboxylic Acids: An Efficient Access to Functionalized Alternating Polyesters. Polym. Chem. 2020, 11 (10), 1708–1712. 10.1039/D0PY00185F. [DOI] [Google Scholar]
  19. Deng Q. H.; Xu H. W.; Yuen A. W. H.; Xu Z. J.; Che C. M. Ruthenium-Catalyzed One-Pot Carbenoid N-H Insertion Reactions and Diastereoselective Synthesis of Prolines. Org. Lett. 2008, 10 (8), 1529–1532. 10.1021/ol800087p. [DOI] [PubMed] [Google Scholar]
  20. Shimomoto H.; Mukai H.; Bekku H.; Itoh T.; Ihara E. Ru-Catalyzed Polycondensation of Dialkyl 1,4-Phenylenebis(Diazoacetate) with Dianiline: Synthesis of Well-Defined Aromatic Polyamines Bearing an Alkoxycarbonyl Group at the Adjacent Carbon of Each Nitrogen in the Main Chain Framework. Macromolecules 2017, 50 (23), 9233–9238. 10.1021/acs.macromol.7b01994. [DOI] [Google Scholar]
  21. Chan W.-W.; Yeung S.-H.; Zhou Z.; Chan A. S. C.; Yu W.-Y. Ruthenium Catalyzed Directing Group-Free C2-Selective Carbenoid Functionalization of Indoles by α-Aryldiazoesters. Org. Lett. 2010, 12 (3), 604–607. 10.1021/ol9028226. [DOI] [PubMed] [Google Scholar]
  22. Galardon E.; le Maux P.; Simonneaux G. J. Chem. Soc., Perkin Trans. 1 1997, 2455. 10.1039/a704687a. [DOI] [Google Scholar]
  23. Huang W. S.; Xu Z.; Yang K. F.; Chen L.; Zheng Z. J.; Xu L. W. Modular Construction of Multifunctional Ligands for the Enantioselective Ruthenium-Catalyzed Carbenoid N-H Insertion Reaction:An Enzyme-like and Substrate-Sensitive Catalyst System. RSC Adv. 2015, 5 (58), 46455–46463. 10.1039/C5RA05804J. [DOI] [Google Scholar]
  24. Padín D.; Varela J. A.; Saá C. Ruthenium-Catalyzed Tandem Carbene/Alkyne Metathesis/N-H Insertion: Synthesis of Benzofused Six-Membered Azaheterocycles. Org. Lett. 2020, 22 (7), 2621–2625. 10.1021/acs.orglett.0c00596. [DOI] [PubMed] [Google Scholar]
  25. Zhou Z.; Tan Y.; Yamahira T.; Ivlev S.; Xie X.; Riedel R.; Hemming M.; Kimura M.; Meggers E. Enantioselective Ring-Closing C-H Amination of Urea Derivatives. Chem. 2020, 6 (8), 2024–2034. 10.1016/j.chempr.2020.05.017. [DOI] [Google Scholar]
  26. Fritz J. A.; Nakhla J. S.; Wolfe J. P. A New Synthesis of Imidazolidin-2-Ones via Pd-Catalyzed Carboamination of N-Allylureas. Org. Lett. 2006, 8 (12), 2531–2534. 10.1021/ol060707b. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Rao W. H.; Yin X. S.; Shi B. F. Catalyst-Controlled Amino- versus Oxy-Acetoxylation of Urea-Tethered Alkenes: Efficient Synthesis of Cyclic Ureas and Isoureas. Org. Lett. 2015, 17 (15), 3758–3761. 10.1021/acs.orglett.5b01741. [DOI] [PubMed] [Google Scholar]
  28. Tamaru Y.; Hojo M.; Higashimura H.; Yoshida Z. Urea as the Most Reactive and Versatile Nitrogen Nucleophile for the Palladium(2+)-Catalyzed Cyclization of Unsaturated Amines. J. Am. Chem. Soc. 1988, 110, 3994–4002. 10.1021/ja00220a044. [DOI] [Google Scholar]
  29. Davies H. M. L.; Grazini M. V. A.; Aouad E. Asymmetric Intramolecular C-H Insertions of Aryldiazoacetates. Org. Lett. 2001, 3 (10), 1475–1477. 10.1021/ol0157858. [DOI] [PubMed] [Google Scholar]
  30. Hansen J. H.; Parr Q.; Pelphrey P.; Jin P.; Autschbach J.; Davies H. M. I. Rhodium(II)-Catalyzed Cross-Coupling of Diazo Compounds. Angew. Chem. Int. Ed. 2011, 50 (11), 2544–2548. 10.1002/anie.201004923. [DOI] [PubMed] [Google Scholar]
  31. Green S. P.; Wheelhouse K. M.; Payne A. D.; Hallett J. P.; Miller P. W.; Bull J. A. Thermal Stability and Explosive Hazard Assessment of Diazo Compounds and Diazo Transfer Reagents. Org. Process Res. Dev. 2020, 24 (1), 67–84. 10.1021/acs.oprd.9b00422. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Haque F. M.; Grayson S. M. The Synthesis, Properties and Potential Applications of Cyclic Polymers. Nat. Chem. 2020, 12 (5), 433–444. 10.1038/s41557-020-0440-5. [DOI] [PubMed] [Google Scholar]
  33. Tawa T.; Ito S. The Role of Hard Segments of Aqueous Polyurethane-Urea Dispersion in Determining the Colloidal Characteristics and Physical Properties. Polym. J. 2006, 38 (7), 686–693. 10.1295/polymj.PJ2005193. [DOI] [Google Scholar]
  34. Reinecker M.; Soprunyuk V.; Fally M.; Sánchez-Ferrer A.; Schranz W. Two Glass Transitions of Polyurea Networks: Effect of the Segmental Molecular Weight. Soft Matter 2014, 10 (31), 5729–5738. 10.1039/C4SM00979G. [DOI] [PubMed] [Google Scholar]
  35. Slot T. K.; Shiju N. R.; Rothenberg G. A Simple and Efficient Device and Method for Measuring the Kinetics of Gas-Producing Reactions. Angew. Chem. 2019, 131 (48), 17433–17436. 10.1002/ange.201911005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Liang Y.; Zhou H.; Yu Z. X. Why Is Copper(I) Complex More Competent than Dirhodium(II) Complex in Catalytic Asymmetric O-H Insertion Reactions? A Computational Study of the Metal Carbenoid O-H Insertion into Water. J. Am. Chem. Soc. 2009, 131 (49), 17783–17785. 10.1021/ja9086566. [DOI] [PubMed] [Google Scholar]
  37. Gillingham D.; Fei N. Catalytic x-h Insertion Reactions Based on Carbenoids. Chem. Soc. Rev. 2013, 42 (12), 4918–4931. 10.1039/c3cs35496b. [DOI] [PubMed] [Google Scholar]
  38. Bergstrom B. D.; Nickerson L. A.; Shaw J. T.; Souza L. W. Transition Metal Catalyzed Insertion Reactions with Donor/Donor Carbenes. Angew. Chem., Int. Ed. 2021, 60, 6864–6878. 10.1002/anie.202007001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Anslyn E. V.; Dougherty D. A.. Modern Physical Organic Chemistry; University Science Books: Sausalito, CA, 2006. [Google Scholar]
  40. Bacchi A.; Pelagatti P.; Pelizzi C.; Rogolino D. Diastereomeric Half-Sandwich Ru(II) Cationic Complexes Containing Amino Amide Ligands. Synthesis, Solution Properties, Crystal Structure and Catalytic Activity in Transfer Hydrogenation of Acetophenone. J. Organomet. Chem. 2009, 694 (19), 3200–3211. 10.1016/j.jorganchem.2009.05.010. [DOI] [Google Scholar]
  41. Chen Z. S.; Yang W. P.; Macosko C. W. Polyurea Synthesis and Properties as a Function of Hard-Segment Content. Rubber Chem. Technol. 1988, 61 (1), 86–99. 10.5254/1.3536179. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ma2c01457_si_002.pdf (4MB, pdf)
ma2c01457_si_001.cif (2.5MB, cif)

Articles from Macromolecules are provided here courtesy of American Chemical Society

RESOURCES