Chain Transfer with Dialkyl Zinc During Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene: Relative Rates, Reversibility and Kinetic Models.

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1 Supporting information Chain Transfer with Dialkyl Zinc During Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene: Relative Rates, Reversibility and Kinetic Models. Heather C. Johnson, Eric S. Cueny, Clark R. Landis* Department of Chemistry, University of Wisconsin Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States Corresponding Author * landis@chem.wisc.edu Contents General experimental considerations S-2 General polymerization procedure S-2 Reversibility of chain transfer to ZnEt 2 analyzed by 13 C NMR spectroscopy S-3 Direct comparison of MWDs of polyoctene obtained using ZnEt 2 and ZnMe 2 S-4 Approximate Mayo analysis S-4 Observing equilibrium between ZnMe 2 and Zn i Pr 2 S-4 Kinetic modeling general considerations S-5 Optimizations to determine k p and k d S-6 Model 1: preferred kinetic model incorporating ZnR 2 exchange equilibria S-8 Comparison of experimental and simulated UV GPC traces (Model 1) S-9 Model 2: reversible Hf-pol/Zn-pol` chain transfer S-11 Model 3: exchange of ethyl group in ZnEtPol S-13 Model 4 no additional chain transfers S-15 Effect of k 2,1 upon Model 4 S-17 Catalyst death vs dormancy from 2,1-misinsertion S-17 References S-20 S-1

2 General experimental considerations Unless otherwise specified, all manipulations were carried out in air- and moisture-free conditions using standard Schlenk line and glovebox techniques. 1 1 and 2 2 were prepared by literature methods. All other compounds were commercial products and used as received. 1, ZnEt 2 and ZnMe 2 were stored as stock solutions in toluene inside a N 2 -filled glovebox ( M and M, respectively). General NMR spectra were collected using Bruker Avance 400 MHz instrument fitted with a Smartprobe, Avance 500 MHz instrument fitted with a DCH cryoprobe, or Avance 600 with TCI-F cryoprobe. Quantitative NMR spectra measuring monomer consumption or end groups were collected using a relaxation delay of 25 s. GPC analyses were performed using a Viscotek GPCmax/VE 2001 instrument fitted with PolyPore columns ( mm) featuring 5 µm particle size from Polymer Laboratories. Samples were eluted with THF at a flow rate of 1 ml/min at 40 C. Polymers were characterized by differential refractive index (RI) and UV (λ 344 nm) detection using a Viscotek Model Tetra Detector Array. Omnisec software (Viscotek, Inc.) was used for initial data processing such as positioning the baseline, setting limits, and applying the molecular weight calibration (relative to polystyrene standards). Further processing was carried out in Excel. General polymerization procedure In a typical experiment, 86 µl of a M toluene solution of 1 was combined with 120 µl of a M toluene solution of [Ph 3 C][B(C 6 F 5 ) 4 ] (i.e. a 1:1.1 mixture of 1:[Ph 3 C][B(C 6 F 5 ) 4 ]). The mixture was heated at 50 C for 3 minutes in an aluminum heating block to form µl of this solution was sampled, and added to a vial containing toluene, 1-octene and ZnR 2 (R = Me, Et) (if applicable), at 50 C, to initiate the polymerization. Polymerizations were quenched with a solution of 2 ( µmol) at selected time points. To the vials, CH 2 Ph 2 (36 µmol) was added as an internal standard. Aliquots were sampled for analysis by 1 H NMR spectroscopy in CDCl 3. The polymer samples (including the NMR samples) were prepared for GPC analysis by dissolving up to 10 ml in THF and diluted such that a 1 mg/ml concentration was achieved. Temperature effects on polymerization The experiments were carried out according to the general procedure above. In each case, 3 was formed at 50 C for 3 minutes. Then, the aluminum heating block was cooled or warmed to the desired temperature before initiating polymerization. Otherwise the protocol is identical to that of the general polymerization procedure. S-2

3 Reversibility of chain transfer to ZnEt 2 analyzed by 13 C NMR spectroscopy Polymerizations were conducted according to the general polymerization procedure described above ([1-octene] 0 = M, [3] 0 = mm, 120 s reaction) with either 2 mm or 0.2 mm ZnEt 2. The polymers were isolated by evaporation of nearly all solvent, then precipitated with MeOH, washed with MeOH, then dried in vacuo. The polymer samples were dissolved in CDCl 3 and 13 C{ 1 H} NMR spectra of the polymers were collected. The NMR spectra were compared with literature values. 3 If chain shuttling were occurring, m x (r)m y stereoerrors should be observed due to shuttling of the polyoctene chain between different enantiomers of the catalyst, as found by Busico and co-workers 4 who observed approximately two-fold increases in the probability for inversion when doubling [AlMe 3 ] in a related system. In our system, <5% stereoerrors were observed with no significant change on increasing [ZnEt 2 ] from 0.2 to 2 Mm ([2.3 ± 1.8]% and [2.9 ± 1.8]%, respectively the large errors are due to a low signal:noise ratio at these concentrations). Examples of the relevant region of the 13 C{ 1 H} NMR spectra are shown in Figure S-1. These data indicate that no significant reversible chain transfer occurs under our conditions. Figure S1 Methine region of 13 C{ 1 H} NMR spectra of polyoctene produced in the presence of 0.2 mm (top) or 2 mm (bottom) [ZnEt 2 ]. S-3

4 Direct comparison of MWDs of polyoctene obtained using ZnEt 2 and ZnMe 2 Figure S2 RI vs retention volume plots for polymers produced in the presence of 1.6 mm ZnEt 2 or ZnMe 2 at 10 s, 30 s and 120 s (similar conversions). Approximate Mayo analysis The chain transfer constant k ex /k p (k ex = rate constant for chain transfer, k p = rate constant for propagation) can be estimated using a Mayo analysis. The chain transfer constant is the slope of a plot of 1/M n vs [ZnMe 2 ]/(112.24*[1-octene]), as shown in the Mayo equation (eq. S-1). In these experiments, polymerizations were conducted in the presence of various amounts of ZnMe 2 and quenched using 2 after several seconds of reaction (ca. 10% conversion). At these short reaction times, we assume that [1-octene] ~ [1-octene] 0. The obtained chain transfer constant is 20 ± octene (S1) M n = M n in the absence of ZnMe = molecular weight of 1-octene in g mol -1. Observing equilibrium between ZnMe 2 and Zn i Pr 2 Zn i Pr 2 (39 µl of a commercial 1.0 M solution in toluene), CH 2 Ph 2 in d 8 -toluene (internal standard, 4 µmol) and d 8 -toluene (367 µl) were added to a NMR tube capped with a septum. ZnMe 2 (74 µl of a commercial 1.2 M solution in toluene) was stored in a gas-tight syringe with the needle piercing the septum of a N 2 -filled vial. A second NMR tube containing ZnMe 2 (74 µl) and CH 2 Ph 2 (4 µmol) and d 8 -toluene (406 µl) was prepared. The NMR spectrometer was warmed to 50 C, and spectra were taken to establish the T 1 values of each species and, then, the concentration of the Zn species. T 1 of ZnMe 2 and Zn i Pr 2 were determined as 10 s and 16 s, respectively. A d 1 value of 30 s was therefore selected for quantitative concentration measurement. The initial concentrations of Zn i Pr 2 and ZnMe 2 were 2.49 and 1.82 mm, respectively. ZnMe 2 in the gastight syringe was injected into the NMR tube containing Zn i Pr 2, the tube was inverted, and inserted into the NMR probe. Within the first timepoint (ca. 3 minutes due to time taken inserting the sample, shimming and the 30 s d 1 ) equilibrium had been reached. The equilibrium constant [Zn i PrMe] 2 /([ZnMe 2 ][Zn i Pr 2 ]) = 4.1. S-4

5 For 1-octene polymerization, the value of k ex2 obtained via fitting of the MWDs (vide infra) is 0.34 M -1 s -1. The ZnMe 2 /Zn i Pr 2 equilibrium can be modelled using the experimentally observed equilibrium constant of 4.1 and the optimized value of k ex2. This simulation (Figure S-3) shows that equilibrium is reached within several minutes. Thus, being unable to observe the approach to equilibrium within minutes by NMR spectroscopy is not unreasonable (if the simulated rate constant is valid on this model system). These experiments show that a value of 0.34 M -1 s -1 for k ex2 is consistent with the data. Figure S3 Simulated approach to equilibrium for ZnMe 2 /Zn i Pr 2 using k ex2 =0.34 M -1 s -1 K eq =[Zn i PrMe] 2 /([ZnMe 2 ][Zn i Pr 2 ) = 4.1. and Kinetic modeling general considerations Landis and co-workers 5 previously showed two ways to simulate molecular weight distributions of (EBI)ZrMe 2 /B(C 6 F 5 ) 3 -catalyzed 1-hexene polymerization that accounts for experimental band broadening: the exponentially-modified Gaussian (EMG) approach, and the band broadening correction (BBC) approach. The EMG approach convolutes discrete calculated concentrations of each polymer i with an EMG function, producing a continuous simulated GPC trace. In contrast, the BBC approach produces discrete values for the RI signal of polymer i through multiplication of the calculated RI signal (km i c i ) by an additional mass term, m i. This mass correction adequately reproduces the effect of band broadening in experimental GPC traces. In the kinetic simulations of (EBI)ZrMe 2 /B(C 6 F 5 ) 3 -catalyzed 1-hexene polymerization, each approach determined the same values, within error, for the optimized rate constants. Therefore, this work uses the simpler BBC approach. Incorporating the BBC approach yields the following equations for the calculation of RI or UV signal corresponding to i monomers: RI i = α 1 * MW i 2 * [Pol i ] UV i = α 2 * MW i * [Pol i ] (S-2) (S-3) Where α 1 and α 2 are scaling factors, MW i = molecular weight of polymer i, and [Pol i ] = concentration of polymer i. The kinetic models were designed in Mathematica, converted to.xml files and imported into the Copasi modelling suite. All optimizations and simulations were performed using Copasi. Molecular weight data from the GPC instrument were treated as previously described. 5 Since S-5

6 the BBC approach provides discrete calculated RI signals calculated as above, rather than a continuous spectrum, 24 discrete points along the MWD (from logmw = to logmw = 6.050) were chosen to simulate the GPC spectra. Where possible, these were spaced ca logmw units apart to simulate the entire distribution equally. However, since the model considers 200 monomer insertions per step, each step in the model constitutes a MW difference of gmol -1. Therefore, owing to the logarithmic scale, the spacing between the first few points in the distribution is larger (e.g. the 1 st 200 insertions leads to logmw = 4.353; the next 200 lead to logmw = 4.653), so the lower MW portions of the MWD are less well fit than the later ones. For this reason, only molecular weight data from 20 s to 120 s (>30% conversion) were considered in the models. The data weighting scheme used relates to the mean square weightings, and the number of data points for each type of data set. Within each heterogeneous data set (e.g. RI values) the data are weighted consistently. Unless otherwise stated, the weightings are: [monomer] = 1, RI = 5x10-6, [vinylene] = 6 x In all models, k i is fixed at 10 5 M -1 s -1 as no induction period was observed experimentally by our methods. This means that essentially all 3 becomes active catalyst. Therefore, the concentration of [3] is equal to the active site concentration. This approximation removes the need to have separate steps in which active catalyst is formed from 3. Since the experimental active site concentration (by quench-labeling) appears constant within error throughout the polymerization time course, this is a reasonable approximation. In all optimizations, [3] is fixed at 45% of experimentally injected catalyst (i.e mm if mm 3 was injected). For the models involving either k ex2 or k ex3 (vide infra), two steps in optimization were often required to achieve satisfactory fits since, when fitting all rate constants, optimizations would often terminate in local minima providing poor fits to experimental data. Using monomer consumption data and experimentally determined concentrations of active sites (fixed across all runs as 45%, mm), the rate constants k p (propagation) and k d (catalyst death) were found. Then, the values of k p and k d were fixed and rate constants for exchange (k ex1 and k ex2, k ex3 or k ex4, where applicable) and chain termination (k 2,1 ) were optimized against experimental data including monomer consumption, molecular weight distributions (RI) at various time points, and [vinylene] after 120 s. Addition of zinc reagents do not affect the rate of polymerization, so this is an appropriate way to model the data. Optimizations to determine k p and k d The values for k p and k d were optimized across a range of concentration regimes. As discussed above, the value of the active catalyst was set to 45% of the experimentally added catalyst, and k i was set to 10 5 M -1 s -1. Excellent agreement between the fits and simulations is observed (Figure S-4). Only the steps shown in the model in Scheme S-1 were considered. S-6

7 initiation k i 3 + mon Hf-Ins k Hf-Ins + mon i Hf-Pol[1] propagation Hf-Pol[n] + 200*mon catalyst death k p 200 Hf-Pol[n+1] Hf-Pol[n] k d Hf-Inact[n] Scheme S1 Initiation, propagation and catalyst death steps Figure S4 Plots of experimental (blue circles) and simulated (red diamonds) [monomer] vs time. Rate constants k p = 892 ± 18 M -1 s -1, (k p 200 = 4.46 ± 0.09 M -1 s -1 ), k d = ± s -1. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = M; (b) [1-octene] 0 = M, [3] 0 = M; (c) [1-octene] 0 = M, [3] 0 = mm; (d) [1-octene] 0 = M, [3] 0 = mm. S-7

8 Model 1: preferred kinetic model incorporating ZnR 2 exchange equilibria The kinetic model that best fits the data is shown below (Scheme S-2). The molecular weight distribution fits across 4 different concentration regimes are shown in Figure S-5. The rate constants for propagation and catalyst death were optimized as above. The rate constants obtained are: k p = 892 ± 18 M -1 s -1, k 2,1 = 0.26 ± 0.01 M -1 s -1, k ex1 = 7493 ± 95 M -1 s -1, k d = ± s -1, k ex2 = 0.34 ± 0.03 M -1 s -1. Several variables were fixed (k i = 10 5 M -1 s -1 ; [3] = 45% active sites, the equilibrium constant K 2 (k ex2 /k ex-2 ) was fixed at 0.24.). The optimized value for the concentration of vinylene end groups is 0.12 mm matches the experimental value of ca mm ([1-octene] 0 = M, [3] 0 = mm). The objective value (sum of squared deviations) is Scheme S2 Model 1. k p 200 = k p /200 S-8

9 Figure S5 Plots of experimental (blue circles) and simulated (red diamonds) RI vs logmw molecular weight distributions for Model 1. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. Comparison of experimental and simulated UV GPC traces (Model 1) As an independent test of our favored kinetic model, simulation of the expected UV-GPC distribution was conducted according to equation S-3 (kinetic modeling general considerations section): the UV signal for polymer i was calculated by multiplying the sum of the concentrations of Hf-bound species [Hf-Pol[i]] and [Hf-Inact[i]] by the molecular weight of i (to correct for the effect of band broadening upon the GPC traces) and a scaling factor (that converts this expression to the 1/transmittance as output from the GPC instrument). To ensure this is an S-9

10 independent test, no additional optimizations were performed. Comparisons between UV expt and UV sim at 20 s and 60 s over a range of experimental conditions is shown in Figure S-6. Overall, there is a good match with experimental data, supporting the robustness of the kinetic model. Note: the dilution required to reach 1 mg/ml polyoctene concentration for GPC analysis means that samples produced at higher conversions (e.g. after 60 s) contain ca mm [chromophore], so noise is increased at higher conversions. Figure S6 Plots of experimental (yellow circles) and simulated (green diamonds) UV vs logmw molecular weight distributions. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1- octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. S-10

11 Model 2: reversible Hf-pol/Zn-pol` chain transfer An alternative kinetic model considered is shown in Scheme S-3. The molecular weight distribution fits across 4 different concentration regimes are shown in Figure S-7. The rate constants for propagation and catalyst death were optimized as above. The rate constants obtained are: k p = 892 ± 18 M -1 s -1, k 2,1 = 0.26 ± 0.01 M -1 s -1, k ex1 = 7473 ± 92 M -1 s -1, k d = ± s -1, k ex3 = 13.3 ± 1.0 M -1 s -1. Several variables were fixed (k i = 10 5 M -1 s -1 ; [Hf] = 45% active sites). The optimized value for the concentration of vinylene end groups is 0.12 mm matches the experimental value of ca mm ([1-octene] 0 = M, [3] 0 = mm). The objective value (sum of squared deviations) is 4.51, similar to that of Model 1. We favor Model 1, despite a slightly higher objective function, since it allows for > 1 chain per Zn center, while Model 2 only allows for a maximum of 1 chain per Zn. Scheme S3 Model 2. k p 200 = k p /200 S-11

12 Figure S7 Plots of experimental (blue circles) and simulated (red diamonds) RI vs logmw molecular weight distributions for Model 2. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. S-12

13 Model 3: direct exchange of ethyl group in ZnEtPol with Hf-Pol Another kinetic model considered is shown in Scheme S-4. The molecular weight distribution fits across 4 different concentration regimes are shown in Figure S-8. The rate constants for propagation and catalyst death were optimized as above. The rate constants obtained are: k p = 892 ± 18 M -1 s -1, k 2,1 = 0.17 ± 0.01 M -1 s -1, k ex1 = 8799 ± 128 M -1 s -1, k d = ± s -1, k ex4 = 37.5 ± 1.0 M -1 s -1. Several variables were fixed (k i = 10 5 M -1 s -1 ; [Hf] = 45% active sites). The fit between the simulated and experimental data are visually worse than for the models involving exchange steps k ex2 or k ex3. The optimized value for the concentration of vinylene end groups is 0.08 mm, lower than the experimental value of ca mm ([1-octene] 0 = M, [3] 0 = mm). This model was not further explored. Scheme S4 Model 3. k p 200 = k p /200 S-13

14 Figure S8 Plots of experimental (blue circles) and simulated (red diamonds) RI vs logmw molecular weight distributions for Model 3. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. S-14

15 Model 4 no additional chain transfers Model 4 features only k ex1 as the only step involving ZnEt 2 (Scheme S-5). The molecular weight distribution fits across 4 different concentration regimes are shown in Figure S-9. The rate constants for propagation and catalyst death were optimized as above. The rate constants obtained are: k p = 892 ± 18 M -1 s -1, k 2,1 = 0.31 ± 0.01 M -1 s -1, k ex1 = 7200 ± 92 M -1 s -1, k d = ± s -1. Several variables were fixed (k i = 10 5 M -1 s -1 ; [Hf] = 45% active sites). The fit between the simulated and experimental data are worse than for the Model 1 or Model 2 with an objective value of 5.69, and the simulated data at 120 s are more bimodal than the data. The optimized value for the concentration of vinylene end groups is 0.15 mm (experimentally, 0.13 ± 0.3 mm) ([1-octene] 0 = M, [3] 0 = mm). Lowering the weighting of [vinylene] results in a lower objective function but raises the simulated [vinylene] to 0.18 mm, outside experimental error. This suggests that the additional chain transfer events considered in Models 1 3 provide subtle yet necessary means of smoothing the molecular weight distributions. Scheme S5 Model 4. k p 200 = k p /200 S-15

16 Figure S9 Plots of experimental (blue circles) and simulated (red diamonds) RI vs logmw molecular weight distributions for Model 4. Experimental conditions: (a) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. S-16

17 Effect of k 2,1 upon Model 4 To demonstrate that small changes in k 2,1 can strongly affect the MWDs, simulations were conducted using Model 4 and the conditions [1-octene] 0 = M, [ZnEt 2 ] 0 = 1.6 mm, [3] 0 = mm (i.e. 45% active sites) rate constants k p = 892 ± 18 M -1 s -1, k 2,1 = 0.31 ± 0.01 M -1 s -1, k ex1 = 7200 ± 92 M -1 s -1, k d = ± s -1, k i = 10 5 M -1 s -1. The values of k 2,1 were fixed at 0, 0.2 M -1 s -1 and 0.4 M -1 s -1. An overlay of the resulting MWDs (and the experimental data) is provided in Figure S-10, showing the significant effect of modest k 2,1 (compared with k p and k ex1 ) values upon the MWD. Figure S10 Simulation of MWD data (at 60 s of polymerization) using Model 4 and altering the value of k 2,1. Catalyst death vs dormancy from 2,1-misinsertion As an alternative to irreversible catalyst death, catalyst dormancy (following a 2,1-misinsertion) was explored and compared with Model 4 (additional chain transfer events are not considered here). The model used is shown in Scheme S-6. There is no catalyst death step. Instead, after undergoing a 2,1-misinsertion of 1-octene (rate constat k mis ), the catalyst lies dormant with the polymer chain intact (Hf-dormant[n]). Then, Hf-dormant[n] can undergo β-hydride elimination to form Hf-Ins and the polymer chain Pol[n] with the rate constant k elim. The model was optimized against experimental data to find the rate constants k p 200, k mis, k elim and k ex1. [3] was fixed at 45% active sites. The resulting rate constants from the optimization are: k p = 1020 ± 20 M -1 s -1 (k p 200 = 5.1 ± 0.1 M -1 s -1 ), k ex1 = 8148 ± 164 M -1 s -1, k mis = 0.41 ± 0.01 M - 1 s -1, k elim = 0.38 ± 0.02 s -1. The MWD fits are adequate (see Figure S-12) but the fits for the monomer consumption show that 1-octene is too rapidly consumed in this model (three different [1-octene] 0 vs time plots are shown in Figure S-11). Additionally, the amount of [vinylene] is overestimated (e.g mm vs 0.13 mm experimentally when [1-octene] 0 = M). S-17

18 initiation 3 + mon Hf-Ins k i k Hf-Ins + mon i Hf-Pol[1] propagation Hf-Pol[n] + 200*mon k p 200 Hf-Pol[n+1] chain transfer to Zn Hf-Pol[n] + ZnEt 2 2,1-misinsertion Hf-Pol[n] + mon k mis k ex1 Hf-Ins + Hf-Dormant[n] EtZn Pol[n] elimination Hf-Dormant[n] k elim Hf-Ins + Pol[n] Scheme S6 Catalyst dormancy model Figure S11 Plots of experimental (blue circles) and simulated (red diamonds) [monomer] vs time for (a) [1-octene] 0 = M, (b) [1-octene] 0 = M, and (c) [1-octene] 0 = M S-18

19 Figure S12 Plots of experimental (blue circles) and simulated (red diamonds) RI vs logmw molecular weight distributions for the dormant catalyst model. Experimental conditions: (a) [1- octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm (b) [1-octene] 0 = M, [3] 0 = mm; [ZnEt 2 ] 0 = 1.6 mm; (c) [1-octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 0.8 mm; (d) [1- octene] 0 = M, [3] 0 = M; [ZnEt 2 ] 0 = 1.6 mm. S-19

20 References (1) Frazier, K.; Boone, H.; Vosejpka, P.; Stevens, J.US A1,2004 (2) Cueny, E. S.; Johnson, H. C.; Anding, B. J.; Landis, C. R., Mechanistic Studies of Hafnium-Pyridyl Amido-Catalyzed 1-Octene Polymerization and Chain Transfer Using Quench- Labeling Methods. J. Am. Chem. Soc. 2017, 139, (3) Galland, G. B.; Da Silva, L. F.; Nicolini, A., Tacticity of Poly-α-olefins from Poly-1-hexene to Poly-1-octadecene. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, (4) Alfano, F.; Boone, H. W.; Busico, V.; Cipullo, R.; Stevens, J. C., Polypropylene Chain Shuttling at Enantiomorphous and Enantiopure Catalytic Species: Direct and Quantitative Evidence from Polymer Microstructure. Macromolecules 2007, 40, (5) Nelsen, D. L.; Anding, B. J.; Sawicki, J. L.; Christianson, M. D.; Arriola, D. J.; Landis, C. R., Chromophore Quench-Labeling: An Approach to Quantifying Catalyst Speciation As Demonstrated for (EBI)ZrMe 2 /B(C 6 F 5 ) 3 -Catalyzed Polymerization of 1-Hexene. ACS Catal. 2016, 6, S-20