Article pubs.acs.org/Macromolecules
Catalytic Synthesis of Secondary Amine-Containing Polymers: Variable Hydrogen Bonding for Tunable Rheological Properties Mitchell R. Perry,† Tannaz Ebrahimi,‡ Erin Morgan,† Peter M. Edwards,† Savvas G. Hatzikiriakos,*,‡ and Laurel L. Schafer*,† †
Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
‡
S Supporting Information *
ABSTRACT: A synthetic protocol using atom-economic, catalytic hydroaminoalkylation and ring-opening metathesis polymerization (ROMP) has been developed for the versatile synthesis of a new class of aryl-substituted secondary aminecontaining polymers. This catalytic route minimizes waste generation and avoids protection/deprotection protocols, postpolymerization modification, and byproduct formation. Different amines can be readily incorporated to access variable hydrogen-bonding characteristics. Thermal and melt rheological characterization has shown the profound effect of hydrogen bonding on the bulk properties of these amine-containing norbornene polymers.
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chelated tantalum phosphoramidate precatalyst 1,35 amine functionalized, cyclic alkene monomers can be prepared in one solvent-free, atom-economic reaction of cyclic diene precursors (Scheme 2). Thus, these two catalytic strategies can be combined to access a flexible and modular synthetic approach while realizing optimized atom and step efficiency. Importantly, hydroaminoalkylation yields unprotected secondary amines that participate in hydrogen bonding to give amine-containing polymers with tunable physical and mechanical properties.38−40
INTRODUCTION There is growing interest in developing approaches to synthesize amine-containing polymers due to their diverse range of applications including antimicrobial materials,1−5 compatibilizers for polymer blends,6−8 CO2 uptake,9−11 water purification,12,13 and catalytic materials.14−20 Current strategies for the synthesis of these high-value products are often plagued by multistep monomer syntheses with inefficient protection/ deprotection protocols1,21−23 and/or the use of postpolymerization modifications.24,25 These traditional routes often result in limited control over amine functionalization and poorly defined polymer microstructures.26 In recent years, ROMP20 has emerged as a powerful tool for the synthesis of functionalized polymers including polyamides.27−30 Notably, ROMP conditions rarely tolerate free primary or secondary pendant amine groups,31,32 presumably due to the fact that these nucleophilic and sterically accessible amines can coordinate and decompose catalytic Ru species.33 More recently, select norbornene monomers with tertiary or secondary alkylamines have been shown to undergo ROMP using a newly reported cationic Mo alkylidene metathesis catalyst.34 However, these reports involve multistep synthetic protocols and stoichiometric reagents to access the requisite norbornene substrates. Thus, to date, the controlled polymerization of unprotected amine-containing monomers has not been a practical and efficient strategy for accessing this broadly useful class of materials. Our approach for addressing synthetic challenges in aminecontaining polymer synthesis exploits our recently developed hydroaminoalkylation catalysts,35,36 coupled with promising results in ROMP of functionalized monomers (Scheme 1).37 Hydroaminoalkylation is an α-C−H alkylation reaction of secondary amines with alkene substrates.36 By using our N,O© XXXX American Chemical Society
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RESULTS AND DISCUSSION Initial investigations focused on the diastereoselective synthesis of norbornene monomers as preferred substrates for ROMP. Monomer M1 incorporates an aryl substituent, while M2 incorporates an alkyl group (Scheme 2). These selectively substituted monomers were easily prepared by stirring precatalyst 1 in a neat mixture of amine and norbornene substrates for 20 h at room temperature. From each reaction, a single diastereomer of the monoalkylated products M1 or M2 could be isolated in 56% yield, following purification by column chromatography. With monomer M1 in hand, ROMP with commercially available second-generation Grubbs catalyst was attempted. Using conditions modified from ROMP of amino acid-derived monomers,21 we began by stirring a solution of M1 and 1 mol % Ru catalyst in THF at room temperature. The progress of the reaction was monitored by taking aliquots and evaluating by NMR spectroscopy. It was determined that 20 h was required to reach full conversion, and this prolonged reaction time (in comparison to ROMP with unfunctionalized Received: February 9, 2016 Revised: May 19, 2016
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Macromolecules Scheme 1. Strategy for Accessing Amine-Containing Polymers by Hydroaminoalkylation and ROMP
polymerize alkyl-substituted M2 yielded no polymeric material, presumably due to the increased nucleophilicity of the substrate that could inhibit Ru-catalyzed ROMP.31 By varying the monomer-to-initiator (M:I) ratio, aminecontaining polymers (P1) with varied molecular weights were prepared.45 The degree of polymerization value (DP) was determined by GPC, and experimental Mn agreed well with theoretical values. End-group analysis by NMR spectroscopy at low M:I ratios (e.g., 20:1, entry 2) further confirmed the DP. Unfortunately, when the M:I was increased to 1000:1, the yield of P1 did not exceed 40%, presumably due to catalyst inhibition/decomposition in the presence of the large growing chain of amine-containing polymer (entries 5 and 6). This result could not be improved using extended reaction times or the more polar solvent chloroform.46 The low Đ of 1.07 (entry 1) suggests a living/controlled polymerization. Further evidence of such behavior was obtained by monitoring monomer conversion and Mn as a function of time (Figure 1). It is noteworthy that the conversion of M1 to
Scheme 2. Monomer Synthesis with Precatalyst 1
monomers, see Supporting Information) was consistent with previous reports of ROMP with amine-containing monomers.21 After quenching with ethyl vinyl ether and adding cold hexanes, a white solid was precipitated and isolated in quantitative yield (Table 1, entry 1). Analysis of the polymeric Table 1. Polymerization Data for M1a
entry
M:Ib
% yieldc
Mnd
DPe
Đf
1 2 3 4 5g 6h
100 20 50 200 1000 1000
>95 >95 >95 >95 40 40
25 800 4 300 11 100 51 200 91 500 108 200
113 19 49 223 399 471
1.07 1.19 1.04 1.08 1.04 1.01
a
Values represent averages of triplicate experiments. bMonomer-toinitiator ratio. cCalculated gravimetrically. dGPC. eDegree of polymeriattion: Mn/MW g/mol. fMw/Mn. gReaction performed in duplicate. h Single reaction performed in chloroform. Figure 1. Conversion of M1 to P1 (100:1 monomer:initiator, rt,) as a function of time as measured by 1H NMR spectroscopy (300 MHz, THF-d8, rt).
1
product by H NMR spectroscopy shows characteristic broadening of signals typical of polymeric material. Furthermore, the disappearance of olefinic C−H resonances of the monomer at 6.1 ppm and concomitant appearance of new olefinic resonances at 5.3 ppm were easily observed. The solid was also characterized by IR spectroscopy and showed characteristic N−H stretches at 3395 cm−1. The resultant materials could be analyzed by gel permeation chromatography (GPC)41 equipped with light scattering capabilities for molecular weight determination. For P1 GPC gave an average Mn of 25 800 (113 repeat units) and a dispersity (Đ) of 1.07. MALDI-TOF mass spectrometry was consistent with the monomer repeat unit as well as the anticipated phenyl and methylene end groups42−44 (see Figures S2 and S3). This proof-of-concept experiment demonstrated that hydroaminoalkylation could be used to easily prepare previously unknown arylamine-substituted polymers via ROMP of this readily accessed class of monomers. Notably, attempts to
P1 requires a full 20 h with the second-generation Grubbs catalyst, as has been previously observed in ROMP of other functionalized monomers.4,44 In particular, previous efforts to polymerize monomers containing free amino groups is markedly slower and lower yielding and gives lower molecular weight product than their protected counterparts.21 Here, the aryl-substituted amine-containing monomers are sluggish but do result in high yields with controlled molecular weights of up to 91 000. Up to a 400:1 monomer-to-initiator ratio, molecular weight increases linearly with conversion while dispersity remains low throughout chain growth (Figure 2). Also, by adding a further 100 equiv of M1 to a completed ROMP reaction (100:1, M1:Ru, THF, 20 h, rt), full conversion was reached within an additional 20 h to give polymer of nearly double the molecular weight while maintaining a low dispersity B
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Figure 2. Mn and dispersity of P1 vs conversion of M1 (100:1 monomer:initiator, rt) as measured by GPC (THF).
(>95% yield, Mn = 48 700, Đ = 1.07). These investigations show that the ruthenium catalyst is not susceptible to deactivation in the presence of secondary arylamine-containing monomers at these concentrations, in contrast to previous reports detailing the difficulties of amine substrates.21,27,37,47,48 Melt Rheology. In P1 the presence of the hydrogen bond donor amine functionalities and the hydrogen bond accepting methoxy groups are anticipated to impact melt viscoelastic measurements. In order to compare and contrast the impact of such hydrogen bonding amine groups, polynorbornene (PNB) was also prepared via polymerization of unfunctionalized norbornene with second-generation Grubbs catalyst (see Supporting Information). Figures 3a and 3b show representative master curves of the viscoelastic moduli of a PNB and a methoxy-functionalized (P1) sample of similar molecular weight.49 The moduli of the PNB sample (Figure 3a) exhibits the classical frequency dependence expected for a linear monodisperse polymer as it shows a plateau modulus, G0N (nearly reached), in storage modulus (G′) and a maximum in the loss modulus (G″) before the crossover frequency. The value of the plateau modulus estimated from several sets of experimental data for PNBs of various molecular weights (Figure S23) is G0N = 1.5 MPa. This value results in an entanglement molecular weight, Me = 2091 g/mol, from Me = ρ0RT/GN0 .50 Therefore, all polymers studied are highly entangled. At the low frequency region G″ exceeds G′ which is the manifestation of liquid-like behavior. However, the functionalized P1 sample (Figure 3b) reveals solid-like elastic behavior as G′ is dominant over G″ over the entire frequency range. These results indicate profound differences in viscoeleastic behavior, presumably due to the formation of transient supramolecular networks as a result of hydrogenbonding interactions.39 Figure 4 shows the viscoelastic moduli G′ and G″ of P1 samples of various molecular weights. These are distinctly different in shape and magnitude compared to unfunctionalized linear PNB polymers where a clear plateau modulus is defined (see Figure 3a). The samples obey the t−T superposition over the range of 90−160 °C examined. These temperatures are well above the measured Tg (vide inf ra, Table 2). Moreover, for moderately high molecular weight samples G′ was found to be higher than G″ over the entire frequency range, a clear manifestation of the presence of strong hydrogen bonding.39 Figure 5 shows the complex viscosity master curves of P1 samples (Tref = 120 °C). At high frequencies, the complex viscosity is independent of molecular weight as short segment relaxation is dominant, as is known for linear monodisperse polymers.50 The plateau in the complex viscosity at low
Figure 3. Master curves (Tref = 120 °C) of the viscoelastic moduli (G′ and G″) and complex viscosity (η*) as a function of the angular frequency (ω) for (a) polynorbornene (PNB) (Mn = 119 700, Đ = 1.35) and (b) P1 (Mn = 94 900, Đ = 1.05).
frequencies (zero-shear viscosity) becomes less defined as molecular weight increases and shows an upturn due to the increased concentration of the hydrogen-bonding moieties.39,51 Zero-shear viscosities of the same samples were calculated using fits of the Cross viscosity model, and these values are plotted in Figure 6.52 As shown for P1, the zero-shear viscosity (η0) scales exponentially with the molecular weight. The exponential growth of the η0 has been reported for star-branched53 and hydrogen-bonding polymers39 and has been attributed to the presence of a different relaxation mechanism due to the presence of static branch points and pseudosolid hydrogenbonding networks, respectively. In the present case, the static branch points are the hydrogen-bonding interactions that provide the additional friction that slows down the global relaxation of the chains.54 This additional friction/relaxation is referred to as sticky reptation and a relevant scaling theory has been proposed to account for this.55,56 However, the unfunctionalized PNB, synthesized via ROMP of norbornene exhibits a signature η0 power law relationship with Mw, consistent with models on linear monodisperse polymers (Figure 6). C
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Macromolecules Table 2. Variably Substituted Norbornene Polymers
a
Degree of polymerization: Mn/MW g/mol. bGlass transition temperatures estimated using DSC thermograms. cGlass transition temperatures estimated using isochronal dynamic temperature sweep tests. dThermal degradation at 5% weight loss. eThermal degradation at 50% weight loss. fCommercial PNB of 2 000 000 Mn.
weight are due to the change in the monomer molecular weight, as all polymers have approximately 100 repeat units (DP, Table 2). Glass transition temperatures of the synthesized polymers were measured using DSC and isochronal dynamic temperature sweep tests (Table 2). The unfunctionalized PNB (Mn = 55 300, entry 5) shows a Tg at 48.5 °C, while the bulky arylamine-substituted samples have higher Tgs (61−82 °C), which is consistent with enhanced intermolecular interactions and hindered segmental motions. TGA results clearly show that unfunctionalized PNB has high thermal stability as it undergoes 5% weight loss at 432.3 °C followed by intense degradation due to polymer backbone decomposition. Alternatively, variously functionalized P1 and P3−P5 have lower thermal stabilities, presumably due to the thermal elimination of the pendant groups. Although the effect of functionalization on the dynamics of the polymer chain is detectable through calorimetric techniques (TGA and DSC), the effect of different para-substituted aniline derivatives could not be distinguished. In contrast, Figure 7 shows the master curves of complex viscosity for similar chain length samples that have been functionalized with different types of substituents (P1, P3−P5). None of the studied samples have reached the terminal region (η0 at low frequencies), suggesting solid-like microstructures as a result of hydrogen-bonded networks. The effect of the different parasubstituents is clear from the different “values” of η0 (albeit not reached in most cases) and the degrees of shear thinning exhibited. Figure 7 shows that the para-fluorinated P3 has the most profound shear thinning behavior, followed by the paramethoxy P1, para-bromo P4, and finally the unsubstituted aniline derivative P5. These results reflect the extent of hydrogen bonding accessible by incorporating differently substituted norbornene polymer backbones. These trends
Figure 4. Master curves of the dynamic moduli (a) G′ and (b) G″ as a function of angular frequency ω for different Mw samples of P1 as a function of reduced angular frequency aTω at 120 °C.
This efficient catalytic approach for the synthesis of aminecontaining polymers, coupled with interesting rheological observations, led us to target related monomers that may provide access to variable hydrogen-bonding properties. By reacting norbornadiene with a variety of N-methylaniline derivatives and 10 mol % 1, we easily accessed various nitrogen-containing monomers. Using this strategy, the established substrate scope of our hydroaminoalkylation catalyst35 could be exploited in the efficient synthesis of amines with four different aryl substituents ranging from the electrondonating p-methoxyaniline derivative (M1) through to the electron-withdrawing p-bromo analogue. Subsequent polymerization proceeded smoothly to give polymers P3−P5 (Table 2) that have been analyzed by GPC (Table S2).57 Analysis of all 1 H NMR spectra of P1 and P3−P5 reveals a broad resonance in the olefinic region, consistent with a trans bias,58 although overlapping resonances complicated definitive integration. Thermal and rheological analyses of P1 and P3−P5 revealed the sensitivity of polymer properties to small changes in the hydrogen bond acceptor substituent in the monomer. These polymers were all prepared using a 100:1 monomer-to-initiator ratio to give monodisperse polymers (Đ, Table 2). These polymers varied in molecular weight from a low of 19 000 for P5 to a high of 30 000 for P4. These differences in molecular D
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Figure 7. Complex viscosity of P1 and P3−P5 (DP of ≅ 100, Mn range of 19 000−30 000) as a function of reduced angular frequency aTω for the melts at 120 °C.
map onto the potential hydrogen bond acceptor character of the para-substituents and demonstrate that the viscoelastic properties of these polymers changes significantly with these substituents while the amine functionality remains consistent. In conclusion, we have developed a flexible, atom-economic, catalytic methodology to synthesize a new class of arylaminesubstituted polynorbornene from norbornadiene and unprotected secondary amines. These novel materials are assembled in only two synthetic steps and the unique properties of these amine-containing materials were benchmarked against unfunctionalized PNB. A variety of arylamine-substituted norbornene derivatives could be efficiently assembled using hydroaminoalkylation. Subsequent ROMP of these monomers could be carried out in a living fashion to yield polymeric materials with unique rheological properties. Notably this protocol avoids amine protection/deprotection strategies and results in less waste generation in the preparation of these desirable materials. Furthermore, substituent effects with representative examples of derivatized anilines have been explored. Thermorheological studies reveal profound effects attributable to the hydrogen-bonding attributes of the specific repeat units. These preliminary results are being extended to synthesize new polymers and copolymers with tunable incorporation of hydrogen-bonding features for accessing variable mechanical properties. Ongoing work explores this new class of polymers for potential application as polymer compatibilizers and antimicrobial materials.
Figure 5. Complex viscosity (η*) master curves of (a) unfunctionalized PNB and (b) P1 of different molecular weights as a function of reduced angular frequency aTω at 120 °C.
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EXPERIMENTAL SECTION
General Details. All chemistry was performed in a nitrogen-filled glovebox or using standard Schlenk techniques unless otherwise stated. All hydroaminoalkylation substrates were purchased from Aldrich and purified by either sublimation or distillation from calcium hydride and degassed by three successive freeze−pump−thaw cycles before use. Anhydrous solvents were obtained from an activated alumina tower and degassed prior to use. Benzene-d6 and toluene-d8 were dried over activated 4 Å molecular sieves and degassed prior to use. Highresolution EI mass spectra (HRMS) were acquired from a Waters/ Micromass LCT spectrometer. GC-MS was performed on an Agilent
Figure 6. Scaling of the zero shear viscosity with Mw of P1 and power law scaling for the unfunctionalized PNBs.
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0.13 g, 56%. 1H NMR (300 MHz, CDCl3): δ 6.83 (d, 3J = 9.0 Hz, 2H, 2 × ArH), 6.63 (d, 3J = 9.0 Hz, 2H, 2 × ArH), 6.14−6.12 (m, 2H, (CH)2), 3.77 (s, 3H, OCH3), 3.52 (br s, 1H, NH), 3.18−3.04 (m, 2H, CH2), 2.88 (s, 1H, CH), 2.76 (s, 1H, CH), 1.75−1.68 (m, 1H, CH), 1.42−1.23 (m, 4H, 2 × CH2). 13C{1H} NMR (75 MHz, CDCl3): δ 152.0 (C), 142.9 (C), 136.8 (CH), 136.5 (CH), 115.0 (2 × CH), 114.0 (2 × CH), 55.9 (CH3), 50.7 (CH2), 45.4 (CH2), 44.6 (CH), 41.8 (CH), 39.1 (CH), 31.4 (CH2). IR (NaCl, cm−1): 3396, 2960, 2866, 1514. HRMS-ESI (m/z) Calcd: 229.1467; found: 229.1467. M2. Product was isolated as a colorless oil after column chromatography (hexanes/triethylamine 14:1) 0.67 g, 56%. 1H NMR (300 MHz, CDCl3): 6.08−6.00 (m, 2H, (CH)2), 2.78−2.77 (m, 1H, NH), 2.68−2.56 (m, 3H, CH2 + CH), 2.43−2.33 (m, 1H, CH), 1.87−1.83 (m, 2H, CH2), 1.74−1.68 (m, 2H, CH2), 1.61−1.47 (m, 2H, 2 × CH), 1.30−0.99 (m, 10H, 5 × CH2). 13C{1H} NMR (75 MHz, CDCl3): δ 136.7 (CH), 136.6 (CH), 57.2 (CH), 53.0 (CH2), 45.3 (CH2), 44.7 (CH), 41.8 (CH), 39.6 (CH), 33.8 (2 × CH2), 31.7 (CH2), 26.3 (CH2), 25.2 (2 × CH2). IR (ATR, cm−1): 3056, 2926, 1737, 1450, 1127. HRMS-ESI (m/z): Calcd; 206.1909 found: 206.1902. M3. Product isolated as a yellow oil after column chromatography (hexanes/ethyl acetate 90:10), 0.18 g, 51%. 1H NMR (300 MHz, CDCl3): δ 6.92−6.86 (m, 2H, 2 × ArH) 6.57−6.53 (m, 2H, 2 × ArH), 6.13−6.07 (m, 2H, (CH)2), 3.38 (overlapped br s, 1H, NH), 3.15− 3.01 (m, 2H, CH2), 2.85−2.86 (m, 1H, CH), 2.73−2.72 (m, 1H, CH), 1.71−1.62 (m, 1H, CH), 1.42−1.32 (m, 3H, CH + CH2), 1.27−1.19 (m, 1H, CH). 13C{1H} NMR (75 MHz, CDCl3): δ 155.8 (d, 1JC−F = 235 Hz, C), 145.0 (2 × CH), 136.9 (CH), 136.5 (C), 115.9 (CH), 115.6 (CH), 113.6 (CH), 113.5 (CH), 50.5 (CH2), 45.4 (CH), 44.6 (CH2), 41.8 (CH), 39.1 (CH), 31.4 (CH2). 19F{1H} NMR (282 MHz, CDCl3): δ −128.8. IR (ATR, cm−1): 3425, 2964, 2869, 1509. HRMSESI (m/z) Calcd: 218.1345; found: 218.1348. M4. Any solid formed during the reaction was filtered through a column of silica gel using DCM as the mobile phase. The filtrate was reduced and was purified by column chromatography (hexanes/ethyl acetate 90:10) 0.44 g, 41%. 1H NMR (300 MHz, CDCl3): δ 7.28−7.25 (m, 2H, 2 × ArH), 6.51−6.48 (m, 2H, 2 × ArH), 6.12 (br s, 2H, (CH)2), 3.76 (br s, 1H, NH), 3.17−3.02 (m, 2H, CH2), 2.89−2.88 (m, 1H, CH), 2.73−2.72 (s, 1H, CH), 1.68−1.63 (m, 1H, CH), 1.41−1.20 (m, 4H, 2 × CH2). 13C{1H} NMR (75 MHz, CDCl3): 147.5 (C), 136.9 (CH), 136.4 (CH), 131.9 (2 × CH), 114.2 (2 × CH), 108.5 (C), 49.6 (CH2), 45.3 (CH), 44.5 (CH2), 41.8 (CH), 38.9 (CH), 31.3 (CH2). IR (ATR, cm−1): 3417, 3344, 2963, 2867, 1595, 1497. HRMSESI (m/z): Calcd: 278.0544; found: 278.0539. M5. Product isolated as a yellow oil after column chromatography (hexanes/ethyl acetate 95:5) 0.92 g, 46%. 1H NMR (300 MHz, CDCl3): δ 7.21−7.16 (m, 2H, 2 × ArH), 6.77−6.68 (m, 1H, ArH), 6.65−6.61 (m, 2H, 2 × ArH), 6.13−6.07 (m, 2H, (CH)2), 3.81 (br s, 1H, NH), 3.21−3.05 (m, 2H, CH2), 2.85 (s, 1H, CH), 2.73 (s, 1H, CH), 1.74−1.65 (m, 1H, CH), 1.36−1.20 (m, 4H, 2 × CH2). 13C{1H} NMR (75 MHz, CDCl3): 148.5 (C), 136.9 (CH), 136.6 (CH), 129.4 (2 × CH), 117.3 (CH), 112.9 (2 × CH), 49.8 (CH2), 45.4 (CH), 44.6 (CH2), 41.8 (CH), 39.1 (CH), 31.4 (CH2). IR (ATR, cm−1): 1504, 1601, 2961. HRMS-ESI (m/z) Calcd: 200.1439; found: 200.1441. General Procedure for Polymer Synthesis. A typical polymerization reaction is described for the polymerization of M1 to generate P1. A solution of monomer (100 equiv, 0.200 g, 0.87 mmol) in 2 mL of dry, degassed THF was prepared under a nitrogen atmosphere. The solution was added to a vial containing Grubbs second-generation catalyst (1 equiv, 7.4 mg, 0.0087 mmol) and a magnetic stir bar. The mixture was stirred at room temperature (22 °C) for 20 h and quenched by adding ethyl vinyl ether (excess, 5 equiv vs [Ru]). After stirring for an additional 30 min, the reaction was added dropwise to a vortex of cold hexanes (−35 °C) to give a white, flocculent solid. The precipitated polymer was collected by filtration and dried in vacuo overnight, and the percent yield was calculated gravimetrically (0.168 g, 84%). Characterization exclusive of GPC was conducted on material isolated from the first precipitation. Additional purification required for GPC was conducted using a THF/hexanes system, and the polymer was dried in vacuo to constant weight prior to drying in a
7890A GC system. IR spectra were obtained on either a Nicolet 4700 FTIR (NaCl) or a PerkinElmer Frontier (ATR) spectrometer. Polynorbornene was prepared following a published literature procedure.1 High molecular weight polynorbornene (Mn = ∼2 000 000 Da) was purchased from Monomer-Polymer and Dajac Labs and used as received. NMR Spectroscopy. NMR spectroscopy was performed on a Bruker Avance 300, 400, or 600 MHz spectrometer at 293 K unless otherwise stated. All coupling values are 3JH−H and reported in hertz. Abbreviations for NMR assignments for peaks are as follows: s = singlet; d = doublet; t = triplet; q = quartet; m = multiple; br = broad. Chemical shift values for polymers are listed as the most abundant peaks in the spectra. Gel Permeation Chromatography. All GPC analysis was conducted on polymers precipitated three times using an appropriate solvent (hexanes or methanol) and dried in vacuo prior to being dried overnight in a vacuum oven. Analysis was performed using Agilent GPC equipped with a Viscostar-II, opti-lab T-rEX and miniDAWN TREOS detectors. GPC analysis was conducted in THF using a flow rate of 0.5 mL/min at 40 °C. All dn/dc values were calculated from 100% mass recovery methods. All samples were analyzed at a concentration of approximately 2 mg/mL. Differential Scanning Calorimetry. Thermal properties of the samples were measured on a TA Instruments Q2000 differential scanning calorimeter calibrated using indium. Analyses were performed in an inert atmosphere (nitrogen) with samples of approximately 5−6 mg in an aluminum pan. All analyses were conducted in duplicate. Samples were heated to 200 °C with a heating rate of 10 °C/min. They were held isothermally at 200 °C for 1 min in order to eliminate any thermal history followed by gradual cooling to −20 °C with a cooling rate of 5 °C/min. The samples were then reheated to 200 °C with a heating rate of 10 °C/min. The glass transition temperatures were determined from the second heating ramp. Thermogravimetric Analysis. Duplicated thermal decomposition results were monitored using a thermogravimetric analysis Shimadzu TGA-50 at a heating rate of 20 °C/min from 30 to 600 °C under an inert atmosphere of nitrogen. Linear Melt Viscoelasticity. Shear measurements were performed using a MCR 501/502 rheometer (Anton Paar), equipped with 8 mm parallel plates. Dynamic time sweep measurements were carried out at an angular frequency of 2 Hz at 120 °C to examine the thermal stability of the samples. Isochronal dynamic temperature sweep tests were performed at 0.1 Hz with a heating rate of 1 °C/min. The dynamic linear viscoelastic measurements were carried out within the linear viscoelastic regime at temperatures in the range from 90 to 160 °C. The dynamic measurements were conducted in the range of 0.01− 100 Hz at a strain of 1%. A gap of 0.5 mm was used to minimize edge effects and ensure a reasonable aspect ratio of plate radius and gap. General Procedure for Monomer Synthesis. Monomers for ROMP derived from norbornadiene were prepared by hydroaminoalkylation (HAA) using the previously reported tantalum phosphoramidate precatalyst 1.35 All monomers described were isolated as colorless or pale yellow oils. HAA produced only one diastereomer of mono(alkylated) product, as shown by GC-MS analysis of the crude reaction mixture (Figure S1). It was previously confirmed to be the exo-diastereomer by X-ray crystallography35 and by comparison to similar compounds in the literature.59 All other diastereomers were assigned by analogy. In some instances, overalkylation of the diene was observed (see Supporting Information). All monomers were purified by column chromatography (SiliaFlash F-60, 230−400 mesh) using the solvent systems listed below. Typical Synthesis of of M1. Known compound.35 To a vial containing 1 (0.10 equiv, 51.7 mg, 0.1 mmol), 4-methoxy-Nmethylaniline (0.137 g, 1.0 mmol) and an excess of norbornadiene (0.146 g, 1.5 mmol) were added to afford a yellow solution. The reaction mixture was stirred for 20 h at room temperature, during which time the mixture turned red. After the allotted time, the mixture was exposed to air, concentrated in vacuo, and purified via column chromatography (hexanes/ethyl acetate 95:5) to yield a yellow oil, F
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vacuum oven overnight. Resonances are labeled as broad singlets (br s) in cases where no distinct splitting or multiplicity could be determined. P1. 1H NMR (300 MHz, CDCl3): δ 6.77−6.74 (m, 2H), 6.57−6.53 (m, 2H), 5.42−5.20 (m, 2H), 3.75 (br s, 3H), 3.11−2.95 (m, 3H), 2.53 (br s, 1H), 1.93 (br s, 2H), 1.64 (br s, 2H), 1.18 (br s, 1H). IR (ATR, cm−1): 3395, 2963, 2869, 1511. P3. 1H NMR (300 MHz, CDCl3): δ 6.88−6.82 (m, 2H), 6.50−6.46 (m, 2H), 5.45−5.23 (m, 2H), 3.56 (br s 1H), 2.99−2.90 (m, 3H), 2.53 (br s, 1H), 1.95 (br s, 2H), 1.65 (br s, 2H), 1.20 (br s, 1H). IR (ATR, cm−1): 3414, 2931, 2861, 1508. P4. 1H NMR (300 MHz, CDCl3): δ 7.21 (br s, 2H), 6.41 (br s, 2H), 5.45−5.24 (m, 2H), 3.76 (br s, 1H), 3.01 (br s, 3H), 2.53 (br s, 1H), 1.95 (br s, 2H), 1.64 (br s, 2H), 1.18 (overlapped br s, 1H). IR (ATR, cm−1): 3413, 2934, 2860, 1594, 1497. P5. 1H NMR (300 MHz, CDCl3): δ 7.20 (br s, 2H), 6.72−6.60 (m, 3H), 5.40−5.28 (m, 2H), 3.91 (br s, 1H), 3.13−2.95 (m, 3H), 2.60 (br s, 1H), 2.01 (br s, 2H), 1.71 (br s, 2H), 1.27 (br s, 1H). IR (ATR, cm−1): 3407, 2931, 2858, 1601, 1505.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00306. Experimental details, molecular characterization (1H, 13C, and 19F NMR spectra) and polymer characterization (GPC traces, DSC, TGA, and rheological analyses) (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*(S.G.H.) E-mail
[email protected]. *(L.L.S.) E-mail
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank NOVA Chemicals and NSERC for financial support of this work. M.R.P. thanks NSERC, and M.R.P., T.E., and P.M.E. thank UBC for postgraduate scholarships. This research was undertaken, in part, thanks to funding from CREATE Sustainable Synthesis and the Canada Research Chairs program.
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REFERENCES
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DOI: 10.1021/acs.macromol.6b00306 Macromolecules XXXX, XXX, XXX−XXX
