Alkynyl Ether Labeling: A Selective and Efficient Approach to Count

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Alkynyl Ether Labeling: A Selective and Efficient Approach to Count Active Sites of Olefin Polymerization Catalysts Yue YU, Roberta Cipullo, and Christophe Boisson ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b04624 • Publication Date (Web): 26 Feb 2019 Downloaded from http://pubs.acs.org on February 27, 2019

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Alkynyl Ether Labeling: A Selective and Efficient Approach to Count Active Sites of Olefin Polymerization Catalysts Yue Yu,*,

†

† Université

Roberta Cipullo‡ and Christophe Boisson†

de Lyon, Univ Lyon 1, CPE Lyon, CNRS, UMR 5265, C2P2 (Chemistry,Catalysis,

Polymers & Processes), Bat 308F, 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France ‡ Department

of Chemical Sciences, Federico II University of Naples, Complesso di Monte S.

Angelo, Via Cintia, 80126 Napoli, Italy

ABSTRACT: Accurately measuring molecular kinetics of catalytic olefin polymerization has been a challenging objective. Many methods have been proposed in the literature but all of them have drawback(s). In this paper, we introduce a labeling method to count active sites employing methyl propargyl ether (MPE) as the quench-labeling agent. It is commercially available, does not react with Al-alkyl species and has a labeling efficiency close to 100%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination-insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-

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supported Ziegler-Natta catalyst in 1-hexene polymerization. The fraction of the active transition metal χ* is found to be 99.5% D) and tetrachloroethane-1,2-d2 (C2D2Cl4, from ARMAR Chemicals, >99.5% D) were used as received. Quenched-flow propylene polymerization The apparatus and polymerization procedure have been reported previously.26 Two vessels, each was loaded with 500 mL n-heptane which contained 23 mM TIBA and was kept at 40 ℃. One vessel was saturated with 1.7 bar propylene. 2 g precatalyst MgCl2/TiCl4/DBP were injected into the other vessel. The timing for precontact started as soon as the precatalyst was injected. When 15 min of precontact was reached, the peristaltic pump was turned on. The monomer-saturated solution was mixed with catalyst slurry at the T junction and initiated polymerization. The length of the tubular reactor allowed the reaction to last for 0.3 s. The exit of the tubular reactor was kept in an MPE/n-heptane solution under the protection of argon so that the reaction mixture was quenched immediately as soon as it eluted out. After 5 min of quenching reaction, acidified


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methanol was poured in to terminate the reaction and to precipitate the polymer. The polymer was dried at 70 ℃ under vacuum overnight. The sample was washed by dissolving it in boiling xylene and precipitating it in methanol. One time of washing was found to be sufficient. Samples quenched with MeOH were prepared by replacing MPE/n-heptane solution with 1 L of acidified MeOH. Due to the instant protonolysis of the product by MeOH, protection with argon was not necessary. 1-hexene polymerization Polymerization procedure with precontact was the same as described in the kinetic study with gas chromatography (GC, see Supporting Information § S1.6) with minor adjustment in the amount of precatalyst and cocatalyst for a few short experiments with precontact of 12 min. Polymerization without precontact was initiated by injecting AlEt3 into the flask which contained n-heptane, 1hexene and precatalyst. A pre-determined amount of MPE solution in n-heptane was injected to quench the polymerization at pre-determined time. After 5 min of quenching reaction, the whole suspension was poured into 300 mL EtOH (containing 3 mL concentrated HCl solution) under stirring to terminate the reaction and to precipitate the polymer. The polymer was dried under vacuum at 100 ℃ for 8 h. Polymer washing was found to be necessary (for details please see Figure S17 and the corresponding text). The following procedure was used: dry polymer was dissolved in 20 mL n-heptane, then precipitated in 300 mL EtOH and dried under vacuum at 100 ℃. Results showed that: 1) there was no dependence of measured χ* on the washing times; and 2) repeated drying of the sample after washing exposed the sample to high temperature and could cause damage to the sample. Therefore, the sample was washed only once.


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Samples quenched with EtOH were prepared by injecting EtOH into the reaction medium at the pre-determined reaction time. GPC characterization of polypropylene Gel permeation chromatography (GPC) was carried out using a Freeslate Rapid-GPC and the following conditions: eluent, 1,2-dichlorobenzene (stabilized with BHT, 0.4 mg mL-1); column, 2×Agilent PLgel 10 μm MIXED-B, 300×7.5 mm, 145 ℃; detector, Polymer Char IR4, 150 ℃. The universal calibration method was employed using monodispersed polystyrene standards (Mn 1.3–3700 KDa). NMR characterization Allyl methyl ether (AME) and methyl propargyl ether (MPE) standard 1H NMR spectra were recorded in C6D6 with a Bruker Avance spectrometer (300 MHz) at room temperature. The following operating conditions were used: zg30 sequence, acquisition time 5.46 s, relaxation delay 2 s, 10 scans. –OMe (δ 3.18 ppm) was used as internal reference. For polypropylene samples, 1H and 13C NMR spectra were recorded using a Bruker Avance III 400 spectrometer equipped with a high-temperature cryoprobe for 5 mm OD tubes, on 45 mg mL-1 polymer solutions in tetrachloroethane-1,2-d2 (with BHT added as stabilizer, [BHT] = 0.4 mg mL1)

at 130 ℃. The following acquisition conditions were used: 1H NMR, 90° pulse; acquisition

time, 2.0 s; relaxation delay, 10.0 s; 16 scans;

13C

NMR, 45° pulse; acquisition time, 2.7 s;

relaxation delay, 5.0 s; 15K scans. For poly(1-hexene) samples, ~40 mg poly(1-hexene) (PH, labeled or non-labeled) was dissolved in 0.5 mL TCE/C6D6 (2/1, v/v). 1H NMR spectra were recorded at 400 MHz with a Bruker Avance


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III spectrometer at 90 ℃ for 5 mm tubes. The following NMR operating conditions were used: zgig30 sequence, acquisition time 2.0 s, relaxation delay 10 s, 1–3K scans depending on signalto-noise ratio. The residual proton signal of the deuterated benzene was used as internal reference (δ 7.15 ppm). The integral of -OMe (δ 3.18 ppm) of the labeling group (produced by insertion of MPE into living chains) and the integral of total alkylic proton were employed to calculate the content of labeled chain ends.


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RESULTS AND DISCUSSION As mentioned previously, a reliable labeling agent should not react with Al-polymeryl, in order to label exclusively the living polymeryl chains. For this reason, we firstly investigated the reactivity of MPE with AliBu3 (TIBA) which was used to mimic Al-polymeryl species. The in-situ 1H NMR experiments (Figure 1, for experimental details please find in Supporting Information § S1.4) clearly demonstrate that no reaction occurred for at least 60 min at room temperature. Further studies proved that MPE is also compatible with AlEt3, AlEt2Cl, MAO and TiCl4 up to 60 ℃ for 30 min, see Figures S1–S8. MPE is shown to be inactive towards Cp2ZrMe2 (Cp = cyclopentadienyl) in the absence of MAO (3 and 4 in Figure S10), indicating that protonolysis of Met-alkyl (Met = Ti or Zr) by HC≡ is unlikely in this study.

Figure 1. Reaction test between MPE and AliBu3 in toluene-d8 (conc. 1M). The quenching efficiency of MPE was investigated by means of GPC with a comparative study of two polypropylene samples prepared under quenched-flow conditions (quenching the reaction of


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tp = 0.3 s with MeOH and MPE, respectively, for 5 min under stirring) mediated by a 4th generation Ziegler-Natta catalyst. The GPC curves of the two polymers obtained under controlled regime (Figure 2) are superimposable, thus indicating an instantaneous quenching with MPE.

Figure 2. GPC traces of two polypropylene samples (Mn = 19 KDa, Mw/Mn = 4.9) prepared under quenched-flow conditions after quenching the reaction with MeOH (dashed line) and MPE (continuous line). The labeling efficiency of polymer chains was investigated by 1H NMR and

13C

NMR

characterization of the polymer samples. The 1H NMR spectra of PP sample quenched with MPE is reported in Figure 3.


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Figure 3. 1H NMR spectra of 1) PP sample quenched with MeOH, 2) PP quenched with MPE, 3) allyl methyl ether and 4) methyl propargyl ether. Peaks marked with * are attributed to the stabilizer BHT. ∆ belongs to the solvent residual C2DHCl4. The resonances of the -OCH2-group at 3.74 ppm and of the -OCH3 group at 3.18 ppm are well visible and are assigned to MPE units at the end of the polypropylene chain (structures B and D in Scheme 1; see also Figure S9 in the Supporting Information). From peak integration the amount of the last inserted MPE units was found to be 0.16mol%, in nice agreement with GPC data (Mn = 19 KDa). Combined with Y = 3.3 mol(C3) mol(Ti)-1, χ* resulted to be 5×10-3 mol mol(Ti)-1 which is in nice agreement with the previously published results measured by quenched-flow approach.26 From the 13C NMR characterization, we obtained, within the experimental error, a similar amount of iBu end-groups (0.16 ± 0.02mol%), resulting from chain initiation at the Ti-iBu bonds generated by TIBA, used as cocatalyst (structure A in Scheme 1). Thus, the fact that [iBu] ~ [MPE] clearly indicates that the labeling efficiency of MPE is close to 100%.


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Scheme 1. The chain ends generated in the presence of quenching agent. Moreover, the disappearance of the resonances of nBu end groups in the

13C

NMR spectrum

(Figure 4) of the sample quenched with MPE compared to the one quenched with MeOH (Structure E in Scheme 1), indicates that the insertion of MPE at active sites is not hampered by the sterically hindered ‘dormant’26 chains resulting from 2,1-insertion of propylene (Structure D in Scheme 1).


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Figure 4.

13CNMR

spectra of the two polypropylene samples prepared under stopped-flow

conditions after quenching the reaction with MeOH (A) and MPE (B). Peaks marked with * are attributed to the stabilizer BHT. In order to elucidate the mechanisms of the labeling reaction, in-situ NMR experiments were carried out on the reaction between a model compound Cp2ZrMe2 and MPE in the absence and presence of MAO. There was no reaction observed for at least eight days when MAO was absent, whereas in the presence of MAO the reaction occurred instantly (Figure S10). It suggests that the coordination vacancy is necessary for the reaction. It is proposed that the labeling reaction probably occurs via a coordination-insertion mechanism that is illustrated in Scheme 2. The results of 2-D NMR experiments (1H–1H COSY and 1H–1H NOESY in Figure S12 and S13, respectively)


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are in line with the structural assignment. More discussion can be found in Supporting Information (§ S1.4 and § S2.3).

Scheme 2. A possible coordination-insertion mechanism of the labeling reaction. Based on the results and analysis, MPE seems to be a valid agent to quantify the amount of active metal in olefin polymerization catalysts. As a last step of this study, we benchmarked the approach by studying the kinetics of 1-hexene polymerization mediated by a MgCl2/TiCl4/butyl phthalate catalyst. We carried out a series of 1-hexene polymerization experiments at different MPE/Ti ratios, precontact times and polymerization times (tp) at 40 ℃ . All polymer samples were characterized via 1H NMR spectroscopy, in order to quantify the content of labeling group ([LbG]) in the samples. A typical spectrum is shown in Figure 5.


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Figure 5. A typical 1H NMR spectrum of MPE-labeled poly(1-hexene). The content of the labeling group [LbG] in the polymer in mol(LbG) mol(C6H12)-1 was calculated as [LbG] =

ANMR,OMe/3 ANMR,alkyl/12

(1)

where ANMR,OMe is the integral of peak of –OMe (peak j) in Figure 5 and ANMR,alkyl is the integral of the alkylic region. Main results are summarized in Table 1.


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Table 1. Results summary of 1-hexene polymerization experiments mediated by a MgCl2/TiCl4/butyl phthalate catalyst with various time of precontact and time of polymerization.

Entry

Precontact [min]

MPE/Ti [mol mol-1]

tp [s]

Y [g(PH) g(cat)-1]

[LbG] [10-4 mol mol-1]

1

0[a]

5

5

0.31

11.6

7.3

2

5

10

1.03

4.4

9.2

3

5

20

1.93

2.5

9.7

4

5

30

2.76

1.7

9.7

5

5

0.29

13.6

8.0

6

5

10

0.62

6.9

8.7

7

5

30

1.82

2.0

7.4

0

30

1.64

-

-

9

5

30

1.04

2.9

6.2

10

15

30

1.48

2.1

6.4

11[c]

15

30

1.64

2.4

7.9

12

15

60

3.48

1.0

7.1

13

15

90

5.32

0.7

7.7

5

20

0.54

4.7

5.2

5

30

0.83

3.4

5.7

5

8

14 15

12[a]

12[b]

30[a]

χ* mol mol-1]

[10-3

[a] Catalyst 1 g, Al/Ti = 17. [b] Catalyst 0.25 g, Al/Ti = 30. For details, please see text. [c] Time of quenching reaction 1 h.


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The fraction of active Ti (last column of Table 1) was calculated as

χ

*

=

[LbG] ∙ MM

Y hexene

NTi

(2)

where [LbG] is the content of labeling group in poly(1-hexene) measured against the total monomeric units, in mol(LbG) mol(C6H12)-1; Y is the yield of polymer, in g(PH) g(cat)-1; MMhexene is the molar mass of 1-hexene, 84.16 g mol-1; NTi is the amount of Ti in 1 g of catalyst, 5.85 × 104

mol in this study.

In all cases we obtained values of χ* < 1%, in good agreement with those previously reported for the same type of catalyst in propene polymerization, using the quenched-flow approach.26 It was found that increasing the equivalents of MPE from 5 to 15 (to Ti) gave almost the same χ* (entries 9 and 10). Increasing the time of labeling reaction from 5 min to 1 h (entry 11) did not significantly change the active site count. This rules out the possibility of multiple insertions of labeling agent, which was a known issue of CO labeling as mentioned in the beginning. The quantification of the protons of the model system Cp2ZrMe2/MAO/MPE also demonstrated that only one MPE molecule inserted into Zr-CH3 (Figure S11). In the absence of precontact between the precatalyst and the cocatalyst (Entries 1–4 in Table 1) χ* reached a plateau within 10 s, indicating that the activation process was completed in a short time. Contrary to a common belief,28, 30-33 when precontact was applied it was found that χ* of this ZNC system (entries 5–13 in Table 1) did not significantly change over polymerization yield 0.3–5.3 g(PH) g(cat)-1 (tp = 5–90 s) (Figure 6). This indicates that χ* does not necessarily increase over polymerization. It likely suggests that all available active sites of a MgCl2-supported ZNC, under


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the conditions of this study, are accessible from the beginning of the polymerization. At longer precontact time (i.e. 30 min) the χ* is slightly lower, and this is in agreement with the well-known fact that longer precontact could result in lower χ*.

Figure 6. Active sites content keeps constant over polymerization. Time of precontact 12 min. (Open markers) 1 g cat, Al/Ti = 17; (full markers) 0.25 g cat, Al/Ti = 30. The present approach can also be used to determine the average kinetic constant of chain propagation . The linear interpolation of the experimental data of Y vs. tp (Figure 7) was used to calculate the average rate of polymerization in the early stage Rp0 (in g(PH) mol(Ti)-1 s-1) which can be expressed as (assuming a first-order monomer dependence): Rp0 = < kp > ∙ [hexene]0 ∙ χ * ∙ MMC6H12

(3)


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where is the average kinetic constant of chain propagation, in M(hexene)-1∙s-1; [hexene]0 = 1 M is the initial concentration of 1-hexene.

Figure 7. Low conversion segments of kinetic profiles with different precontact time. (●) without precontact; (□ and ■) 12 min precontact, open markers,1 g cat, Al/Ti = 17, full markers, 0.25 g cat, Al/Ti = 30 and (▲) 30 min precontact. For each series of experiments with a given precontact time (12 or 30 min), was calculated with the average value of χ* (plateau values employed for the series without precontact), which resulted to be in the order of 102 M-1s-1. These values are one order of magnitude lower than those reported for propene polymerization, as one should expect considering the bulkiness of the monomer. As a matter of fact, the value of for propylene polymerization has been demonstrated to be one order of magnitude lower than ethylene polymerization.25 From the data


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reported in Table 2 it is evident that longer precontact resulted in lower Rp values, due to the combined effects of decreased χ* and decreased . Table 2. Effects of precontact on kinetic parameters, assuming Rp to be 1st-order to [hexene]. Precontact [min] 0 12 30

[102

g(PH)

Rp0 -1 mol(Ti) s-1] 1.6 0.9 0.5

[10-3

χ* mol mol(Ti)-1] 9.5 7.3 5.4

[102

-1 M(hexene) s-1] 2.0 1.5 1.0

CONCLUSIONS In this paper, we showed that the commercially available MPE does not react with Al-alkyl species and selectively labels the polyolefin chains attached to the catalytic metal regardless of their regiochemistry. This makes MPE a unique labeling molecule to quantify and follow the kinetic parameters of olefin polymerization catalysts in the course of polymerization. The performance of MPE was benchmarked in a case study of 1-hexene polymerization mediated by a 4th generation Ziegler-Natta catalyst. We believe that due to its well-defined chemistry, propargyl ethers can be expanded into a family of quench-labeling agents for dedicated purposes.


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AUTHOR INFORMATION Corresponding Author *[email protected]

ASSOCIATED CONTENT Supporting Information. Chemical compatibility of the labeling agent MPE, 1H–13C DEPT-HSQC characterization of a labeled polypropylene sample, mechanistic study of the labeling reaction, PSD and morphology of the catalyst, kinetics of 1-hexene polymerization measured by GC, and sample treatment on the labeled poly(1-hexene)

ACKNOWLEDGMENT The authors would like to thank Prof. Vincenzo Busico, Dr. Christian Ehm (LSP@University of Naples), Dr. Timothy McKenna, Dr. Jean Raynaud, Dr. Vincent Monteil (LCPP@C2P2) and Dr. Mostafa Taoufik (LCOMS@C2P2) for valuable suggestions, Dr. Carlos Fernández de Alba, Dr. Fernande Da Cruz-Boisson (IMP@INSA) and Mrs. Christine Lucas (LCOMS@C2P2) for the access to the NMR service. Dr. Yu would like to particularly thank Dr. Shenai Hu (CFLC@Xiamen University) for her support and encouragement.


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REFERENCES 1. Liu, Z. X.; Somsook, E.; White, C. B.; Rosaaen, K. A.; Landis, C. R. Kinetics of initiation, propagation, and termination for the [rac-(C2H4(1-indenyl)2)ZrMe][MeB(C6F5)3]-catalyzed polymerization of 1-hexene. J. Am. Chem. Soc. 2001, 123, 11193-11207. 2. Natta, G.; Pasquon, I. The kinetics of the stereospecific polymerization of α-olefins. Adv. Catal. 1959, 11, 1-66. 3. Chumaevskii, N. B.; Zakharov, V. A.; Bukatov, G. D.; Kuznetzova, G. I.; Yermakov, Y. I. Study of mechanism of propagation and transfer-reactions in polymerization of olefins by ZieglerNatta catalysts .1. Determination of number of propagation centers and rate constant. Makromol. Chem. Macromol. Chem. Phys. 1976, 177, 747-761. 4. Chien, J. C. W. Kinetics of ethylene polymerization catalyzed by bis-(cyclopentadienyl)titanium dichloride dimethylaluminum chloride. J. Am. Chem. Soc. 1959, 81, 86-92. 5. Cipullo, R.; Mellino, S.; Busico, V. Identification and count of the active sites in olefin polymerization catalysis by oxygen quench. Macromol. Chem. Phys. 2014, 215, 1728-1734. 6. Feldman, C. F.; Perry, E. Active centers in the polymerization of ethylene using titanium tetrachloride-alkylaluminum catalysts. J. Polym. Sci. 1960, 46, 217-231. 7. Vozka, P.; Mejzlík, J. Determination of the number of active centers in Ziegler-Natta polymerization of propene using sulfur-containing terminating agents, 1. Application of carbon disulfide. Makromol. Chem. 1989, 190, 1489-1499. 8. Fan, Z. Q.; Feng, L. X.; Yang, S. L. Distribution of active centers on TiCl4/MgCl2 catalyst for olefin polymerization. J. Polym. Sci. A Polym. Chem. 1996, 34, 3329-3335. 9. Shiono, T.; Ohgizawa, M.; Soga, K. Reaction between carbon monoxide and a Tipolyethylene bond with a MgC12-supported TiCl4 catalyst system. Makromol. Chem. Macromol. Chem. Phys. 1993, 194, 2075-2085. 10. Shiono, T.; Ohgizawa, M.; Soga, K. Reaction of the Ti-polyethylene bond with carbonmonoxide over the bis(cyclopentadienyl)titanium dichloride methylaluminoxane catalyst system. Polymer 1994, 35, 187-192. 11. Busico, V.; Guardasole, M.; Margonelli, A.; Segre, A. L. Insertion of carbon monoxide into Zr-polymeryl bonds: "Snapshots" of a running catalyst. J. Am. Chem. Soc. 2000, 122, 5226-5227. 12. Cueny, E. S.; Johnson, H. C.; Anding, B. J.; Landis, C. R. Mechanistic studies of hafniumpyridyl amido-catalyzed 1-octene polymerization and chain transfer using quench-labeling methods. J. Am. Chem. Soc. 2017, 139, 11903-11912. 13. 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)ZrMe2/B(C6F5)3-catalyzed polymerization of 1-hexene. ACS Catal. 2016, 6, 7398-7408. 14. DABAL-Me3. Sigma-Aldrich. Available online: https://www.sigmaaldrich.com/chemistry/chemical-synthesis/technology-spotlights/dabal.html (accessed on 15. Oct. 2018). 15. Schäfer, G.; Matthey, C.; Bode, J. W. Facile synthesis of sterically hindered and electrondeficient secondary amides from isocyanates. Angew. Chem. Int. Ed. 2012, 51, 9173-9175. 16. Keii, T.; Terano, M.; Kimura, K.; Ishii, K. A kinetic argument for a quasi-living polymerization of propene with a MgCl2-supported catalyst. Makromol. Chem. Rapid Commun. 1987, 8, 583-587. 17. Terano, M.; Kataoka, T.; Keii, T. Stopped-flow polymerization of propene with typical MgCl2-supported high-yield catalysts. J. Mol. Catal. 1989, 56, 203-210.


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18. Busico, V.; Cipullo, R.; Esposito, V. Stopped-flow polymerizations of ethene and propene in the presence of the catalyst system rac-Me2Si(2-methyl-4-phenyl-1indenyl)2ZrCl2/methylaluminoxane. Macromol. Rapid Commun. 1999, 20, 116-121. 19. Liu, B. P.; Matsuoka, H.; Terano, M. Stopped-flow techniques in Ziegler catalysis. Macromol. Rapid Commun. 2001, 22, 1-24. 20. Song, F. Q.; Cannon, R. D.; Bochmann, M. Zirconocene-catalyzed propene polymerization. A quenched-flow kinetic study. J. Am. Chem. Soc. 2003, 125, 7641-7653. 21. Di Martino, A.; Broyer, J. P.; Spitz, R.; Weickert, G.; McKenna, T. F. A rapid quenched-flow device for the characterisation of the nascent polymerisation of ethylene under industrial conditions. Macromol. Rapid Commun. 2005, 26, 215-220. 22. Di Martino, A.; Weickert, G.; McKenna, T. F. L. Contributions to the experimental investigation of the nascent polymerisation of ethylene on supported catalysts, 1. A quenched-flow apparatus for the study of particle morphology and nascent polymer properties. Macromol. React. Eng. 2007, 1, 165-184. 23. Ranieri, M. M.; Broyer, J. P.; Cutillo, F.; McKenna, T. F. L.; Boisson, C. Site count: Is a highpressure quenched-flow reactor suitable for kinetic studies of molecular catalysts in ethylene polymerization? Dalton Trans. 2013, 42, 9049-9057. 24. Thakur, A.; Poonpong, S.; Terano, M.; Taniike, T. New quenching method for improving large-scale stopped-flow technique. Macromol. React. Eng. 2014, 8, 766-770. 25. Cipullo, R.; Melone, P.; Yu, Y.; Iannone, D.; Busico, V. Olefin polymerisation catalysts: When perfection is not enough. Dalton Trans. 2015, 44, 12304-12311. 26. Yu, Y.; Busico, V.; Budzelaar, P. H. M.; Vittoria, A.; Cipullo, R. Of poisons and antidotes in polypropylene catalysis. Angew. Chem. Int. Edit. 2016, 55, 8590-8594. 27. Kissin, Y. V.; Mink, R. I.; Nowlin, T. E. Ethylene polymerization reactions with Ziegler– Natta catalysts. I. Ethylene polymerization kinetics and kinetic mechanism. J. Polym. Sci. A Polym. Chem. 1999, 37, 4255-4272. 28. Taniike, T.; Wada, T.; Kouzai, I.; Takahashi, S.; Terano, M. Role of dispersion state of Ti species in deactivation of MgCl2-supported Ziegler-Natta catalysts. Macromol. Res. 2010, 18, 839844. 29. Nikolaeva, M. I.; Matsko, M. A.; Mikenas, T. B.; Echevskaya, L. G.; Zakharov, V. A. Copolymerization of ethylene with α-olefins over supported titanium–magnesium catalysts. I. Effect of polymerization duration on comonomer content and the molecular weight distribution of copolymers. J. Appl. Polym. Sci. 2012, 125, 2034-2041. 30. Jiang, B.; Weng, Y.; Zhang, S.; Zhang, Z.; Fu, Z.; Fan, Z. Kinetics and mechanism of ethylene polymerization with TiCl4/MgCl2 model catalysts: Effects of titanium content. J. Catal. 2018, 360, 57-65. 31. Boor, J. Growth of the polymer particle. In Ziegler–Natta Catalysts Polymerizations, Boor, J., Ed. Academic Press: New York, 1979; pp 180-212. 32. Boor, J. Kinetics. In Ziegler–Natta Catalysts Polymerizations, Boor, J., Ed. Academic Press: New York, 1979; pp 464-511. 33. Mori, H.; Yoshitome, M.; Terano, M. Investigation of a fine-grain MgCl2-supported Ziegler catalyst by stopped-flow propene polymerization: Model for the formation of active sites induced by catalyst fragmentation during polymerization. Macromol. Chem. Phys. 1997, 198, 3207-3214.


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BRIEFS A quench-labeling method employing an alkynyl ether was proposed to reliably measure molecular kinetics of catalytic olefin polymerization SYNOPSIS


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Alkynyl Ether Labeling: A Selective and Efficient Approach to Count

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