Synthesis of Ultrahigh Molecular Weight Polymers with Low PDIs by Polymerizations of 1-Decene, 1-Dodecene, and 1-Tetradecene by Cp*TiMe2(O-2,6-iPr2C6H3)–Borate Catalyst

Polymerizations of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) by Cp*TiMe2(O-2,6-iPr2C6H3) (1)–[Ph3C][B(C6F5)4] (borate) catalyst have been explored in the presence of Al cocatalyst. The polymerizations of DC and DD, in n-hexane containing a mixture of AliBu3 and Al(n-C8H17)3, proceeded with high catalytic activities in a quasi-living manner, affording high molecular weight polymers (activity 4120–5860 kg-poly(DC)/mol-Ti·h, Mn for poly(DC) = 7.04–7.82 × 105, after 20 min at −30 °C). The PDI (Mw/Mn) values in the resultant polymers decreased upon increasing the ratio of Al(n-C8H17)3/AliBu3 with decreasing the activities at −30 °C. The PDI values also became low when these polymerizations were conducted at low temperatures (−40 or −50 °C); high molecular weight poly(DD) with low PDI (Mn = 5.26 × 105, Mw/Mn = 1.16) was obtained at −50 °C. The TD polymerization using 1–borate–AliBu3 catalyst (conducted in n-hexane at −30 °C) afforded ultrahigh molecular weight poly(TD) (Mn = 1.02 × 106, Mw/Mn = 1.38), and the PDI values also decreased with increasing the Al(n-C8H17)3/AliBu3 ratio.


Introduction
Design of molecular catalysts for olefin polymerization has been considered as an important subject in synthesis of new polymers with specified functions. The recent progress in the catalyst developments provides new possibilities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Although crystalline isotactic polypropylene has been widely used in our daily life, use of amorphous poly(α-olefin)s (APAOs) showed less attention due to their inherent stickiness and softness. APAOs possess high melt-flow rate with low density, and are used in hot melt applications, these also improve adhesion on wood and polypropylene, and improve the free-flowing ability of their granules. It has been known recently that ultrahigh molecular weight poly(α-olefin)s can be used as drag reducing agents (DRAs) in pipeline transport methods for crude oil and petroleum products, because of their ability to reduce pumping power and increase piping system capacity [18][19][20][21]. Moreover, poly(α-olefin)s with alkyl chain length greater than six have bottlebrush architecture (branched macromolecules with a high graft density along their backbone) [22][23][24][25], and are the simplest bottlebrush polymers, with their backbone and side chains consisting of alkanes.
As shown in Table 2, the polymerization of DC at −30 • C (runs 1-3) proceeded with high catalytic activities (4120-5860 kg-polymer/mol-Ti·h after 20 min) without significant catalyst deactivation to afford high molecular weight poly(DC)s (M n = 7.04-7.82 × 10 5 ), and the M n values increased over time course without increasing the PDI (M w /M n ) values. It turned out that the PDI values decreased upon increasing the Al(n-C 8 H 17 ) 3 /Al i Bu 3 molar ratio, whereas the catalytic activity decreased with increasing the ratio (runs 1-3). As shown in Figure 1a (shown below), rather linear relationships between the M n values and the polymer yields (turnover numbers, TON) were observed, suggesting that these polymerizations proceeded in a (quasi) living manner. It also turned out that the PDI values became low when the polymerization was conducted at Similarly, as shown in Table 3 upon increasing the Al(n-C 8 H 17 ) 3 /Al i Bu 3 molar ratio, whereas the catalytic activity decreased with increasing the ratio. As also shown in Figure 1b (shown below), rather linear relationships between the M n values and the polymer yields (turnover numbers, TON) suggest that these polymerizations also proceeded in a (quasi) living manner.  It was also revealed that the PDI values became low when the polymerization was conducted at −40 • C (run 9), although the catalytic activity decreased at −40 • C [activity after 20 min: 5020 kg-polymer/mol-Ti·h (run 8, at −30 • C) vs. 1720 (run 9, at −40 • C)]. As shown in Figure 1b, a relatively good linear relationship between M n value and the polymer yield consistent with rather low PDI values (M w /M n = 1.22-1.29) clearly suggests that the polymerization proceeded in a (quasi) living manner. Moreover, the PDI value became low (M w /M n = 1.11-1.18) when the polymerization was conducted at −50 • C. The M n value in the resultant polymers increased over time course consistent with low PDI values; high molecular weight poly(DD) with low PDI (M n = 5.26 × 10 5 , M w /M n = 1.14) could be thus obtained after 2 h.
As shown in Figure 1, good linear relationships between the M n values and the polymer yields (TONs) were observed without increasing the PDI values in all cases, suggesting that these polymerizations proceeded in a (quasi) living manner. In particular, the polymerizations at −40 • C afforded polymers with low PDI values, the results thus strongly indicate a possibility of living polymerization under these conditions. The resultant poly(DD)s showed similar thermal property (melting temperature (T m ) = −24 • C) to those prepared by Cp*TiCl 2 (O-2,6-i Pr 2 C 6 H 3 )-MAO catalyst [28], whereas T m values increased upon increasing methylene units in the alkyl side chain (poly(1-hexadecane) = 26 • C, poly(1-octadecene = 42 • C) due to called side chain crystallization [28].
It turned out that, as observed in polymerizations of DC and DD, these polymerizations proceeded without significant decreases in the catalytic activities (based on polymer yields), whereas the observed activity decreased with decreasing the Al i Bu 3 /Al(n-C 8 H 17 ) 3 molar ratios. The M n values in the resultant polymers increased upon increasing the polymer yields (over time course) with consistent PDI values, and good linear relationships between the M n values and the polymer yields were thus obtained, as shown in Figure 2a. These results clearly suggest that these polymerizations proceed in a (quasi) living manner. It also turned out that the M n values after certain turnovers increased upon decreasing the Al i Bu 3 /Al(n-C 8 H 17 ) 3 molar ratios (eg. M n = 7.83 × 10 5 (14,400 turnovers, run 11) vs. M n = 7.34 × 10 5 (15,900 turnovers, run 12) vs. M n = 5.26 × 10 5 (14,300 turnovers, run 13)) along with decreasing the PDIs. The results thus suggest an increase of percentage of catalytically active species in situ upon increasing the ratio of Al(n-C 8 H 17 ) 3 , although we could not estimate the exact number of catalytically active species at this moment (because the M n values were estimated on gel-permeation chromatography (GPC) trace vs. polystyrene standards). Poly(TD) with ultrahigh molecular weight (M n = 1.02 × 10 6 , M w /M n = 1.38) could be thus obtained in the polymerization using 1-borate-Al i Bu 3 catalyst (run 11, after 2 h).  Figure 2b shows selected 13 C NMR spectra (in CDCl 3 at 25 • C) for poly(DC) and poly(DD). It is clear that the resultant polymers do not have stereo-regularity (atactic polymers) [49], and as observed in the spectra in poly(1-hexene) [50], resonances ascribed to 2,1-or other insertion units could not be found. The results strongly suggest that these polymerizations proceeded with (in high certainty) 1,2-insertion manner. in kg-polymer/mol-Ti·h. e TON (turnovers) = molar amount of 1-decene consumed/mol·Ti. f GPC data in THF vs. polystyrene standards. Figure 2b shows selected 13 C NMR spectra (in CDCl3 at 25 °C) for poly(DC) and poly(DD). It is clear that the resultant polymers do not have stereo-regularity (atactic polymers) [49], and as observed in the spectra in poly(1-hexene) [50], resonances ascribed to 2,1-or other insertion units could not be found. The results strongly suggest that these polymerizations proceeded with (in high certainty) 1,2-insertion manner.

Materials and Methods
All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox unless otherwise specified. All chemicals used were of reagent grade and were purified by the standard purification procedures. Anhydrous grade of toluene (Kanto Kagaku Co. Ltd., Tokyo, Japan) was transferred into a bottle containing molecular sieves (mixture of 3A and 4A 1/16, and  Table 4. (b) 13 C NMR spectrum (in CDCl 3 at 25 • C) for poly(1-decene) (top, sample, run 1) and poly(1-dodecene) (bottom, sample, run 10).

Materials and Methods
All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox unless otherwise specified. All chemicals used were of reagent grade and were purified by the standard purification procedures. Anhydrous grade of toluene (Kanto Kagaku Co. Ltd., Tokyo, Japan) was transferred into a bottle containing molecular sieves (mixture of 3A and 4A 1/16, and 13X) in the drybox, and was used without further purification. Reagent grades 1-decene (TCI Co., Ltd., Tokyo, Japan), 1-dodecene (TCI Co., Ltd.), 1-tetradecene (TCI Co., Ltd.) were stored in bottles in the drybox and were passed through an alumina short column prior to use. Syntheses of Cp*TiMe 2 (O-2,6-i Pr 2 C 6 H 3 ) (1) was according to our previous report [50]. Ph 3 CB(C 6 F 5 ) 4 was purchased from Asahi Glass Co. Ltd., and was used as received in the drybox.
All 1 H and 13 C NMR spectra were recorded on a Bruker AV 500 spectrometer (500.13 MHz for 1 H; 125.77 MHz for 13 C), and all chemical shifts are given in ppm and are referred to SiMe 4 . 13 C NMR spectra for the resultant polymers were recorded with proton decoupling, and the pulse interval was 5.2 s, the acquisition time was 0.8 s, the pulse angle was 90 • , and the number of transients accumulated was about 6000. The polymer samples for analysis were prepared by dissolving the polymers in CDCl 3 solution, and the spectra was measured at 25 • C. Molecular weights and the molecular weight distributions of the resultant polymers were measured by gel-permeation chromatography (GPC). HPLC grade THF was used for GPC and was degassed prior to use. GPC was performed at 40 • C on a Shimadzu SCL-10A using a RID-10A detector (Shimadzu Co. Ltd.) in THF (containing 0.03 wt. % of 2,6-di-tert-butyl-p-cresol, flow rate 1.0 mL/min). GPC columns (ShimPAC GPC-806, 804 and 802, 30 cm × 8.0 mm diameter, spherical porous gel made of styrene/divinylbenzene copolymer, ranging from <10 2 to 2 × 10 7 MW) were calibrated versus polystyrene standard samples. The molecular weight was calculated by a standard procedure based on the calibration with standard polystyrene samples.
Typical polymerization procedures were as follows: 1-decene (30 mL), n-hexane (30 mL) and a prescribed amount of Al i Bu 3 [and Al(n-C 8 H 17 ) 3 ] was added into a 100 mL round-bottom flask connected to three-way valves under N 2 , the solution was then cooled to −30 • C. A toluene solution containing 1 (2.0 µmol/mL) [pre-treated with 2.0 eq. of Al i Bu 3 at −30 • C] was added into the mixture, and the polymerization was then started by the addition of a prescribed amount of toluene solution containing Ph 3 CB(C 6 F 5 ) 4 (2.0 µmol/mL). A prescribed amount (3.0 mL) of the reaction mixture was removed via a syringe from the polymerization solution to monitor the time course, and the sample solution was then quickly poured into i PrOH (150 mL) containing HCl (10 mL). The resultant polymer was collected and was adequately washed with i PrOH and then dried in vacuo.

Conclusions
We have shown that polymerizations of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) using Cp*TiMe 2 (O-2,6-i Pr 2 C 6 H 3 ) (1)-[Ph 3 C][B(C 6 F 5 ) 4 ] (borate) catalyst proceeded with high catalytic activities, affording (ultra)high molecular weight polymers. The polymerizations of DC and DD, in n-hexane containing a mixture of Al i Bu 3 and Al(n-C 8 H 17 ) 3 at −30 • C, proceeded with high catalytic activities (4120-5860 kg-poly(DC)/mol-Ti·h) without catalyst deactivation, affording high molecular weight polymers (M n for poly(DC) = 7.04-7.82 × 10 5 after 20 min). The PDI (M w /M n ) values were affected by the ratio of Al(n-C 8 H 17 ) 3 /Al i Bu 3 as well as the polymerization temperature. Synthesis of high molecular weight poly(DD) with low PDI (M n = 5.26 × 10 5 , M w /M n = 1.16) could be attained at −50 • C. The TD polymerization using 1-borate-Al i Bu 3 catalyst (conducted in n-hexane at −30 • C) also afforded ultrahigh molecular weight poly(TD) (M n = 1.02 × 10 6 , M w /M n = 1.38). The results presented here are rare demonstrations for successful synthesis of (ultra)high molecular weight bottlebrush poly(α-olefin)s with narrow molecular weight distributions by polymerization of higher α-olefins, which proceeded in a (quasi) living manner. The fact should be important for synthesis of new polyolefins as well as design of efficient molecular catalysts for olefin polymerization.