molecules Article Synthesis of Ultrahigh Molecular Weight Polymers with Low PDIs by Polymerizations of 1-Decene, 1-Dodecene, and 1-Tetradecene by i Cp*TiMe2(O-2,6- Pr2C6H3)–Borate Catalyst Kotohiro Nomura * , Sarntamon Pengoubol and Wannida Apisuk Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan; [email protected] (S.P.); [email protected] (W.A.) * Correspondence: [email protected]; Tel./Fax: +81-42-6772547 Academic Editor: Giovanni Ricci Received: 29 March 2019; Accepted: 23 April 2019; Published: 25 April 2019 Abstract: Polymerizations of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) by i Cp*TiMe2(O-2,6- Pr2C6H3)(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 i Al Bu3 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 5 · poly(DC) = 7.04–7.82 10 , after 20 min at 30 ◦C). The PDI (Mw/Mn) values in the resultant × − i polymers decreased upon increasing the ratio of Al(n-C8H17)3/Al Bu3 with decreasing the activities at 30 ◦C. The PDI values also became low when these polymerizations were conducted at low − 5 temperatures ( 40 or 50 ◦C); high molecular weight poly(DD) with low PDI (Mn = 5.26 10 , − − i × Mw/Mn = 1.16) was obtained at 50 ◦C. The TD polymerization using 1–borate–Al Bu3 catalyst − 6 (conducted in n-hexane at 30 ◦C) afforded ultrahigh molecular weight poly(TD) (Mn = 1.02 10 , − i × Mw/Mn = 1.38), and the PDI values also decreased with increasing the Al(n-C8H17)3/Al Bu3 ratio. Keywords: polymerization; titanium complex; catalyst; α-olefin; half-titanocene; borate 1. 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 [1–17]. 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 [18–21]. 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) [22–25], and are the simplest bottlebrush polymers, with their backbone and side chains consisting of alkanes. As shown below (Table1), polymerization of α-olefin (1-hexene, 1-octene, 1-decene, etc.) by ordinary metallocene catalysts gave oligomers [26–28]. Several examples [28–33] were known for t synthesis of (ultra)high molecular weight poly(1-hexene)s by using [2,2-(O-4-Me-6- Bu-C6H3)2S]TiCl2 (in the presence of specified modified MMAO) [31,32], or (C5HMe4)2HfCl2 (under ultrahigh Molecules 2019, 24, 1634; doi:10.3390/molecules24081634 www.mdpi.com/journal/molecules Molecules 2019, 24, x 2 of 11 (in the presence of specified modified MMAO) [31,32], or (C5HMe4)2HfCl2 (under ultrahigh pressure) [29]. One example was known for synthesis of isotactic poly(1-hexene)s with ultrahigh molecular Molecules 2019, 24, 1634 2 of 10 weights by titanium complexes containing diamine bis(phenolate) ligands [30]. Several examples were also known for synthesis of poly(α-olefin)s with rather high molecular weights [27,34–42]. pressure)However, [29 synthesis]. One example of ultrahigh was knownmolecular for weight synthesis polymers of isotactic by polymerization poly(1-hexene)s of withhigher ultrahigh α-olefins molecular(1-decene, weights 1-dodecene, by titanium 1-tetradecene complexes, etc.) containing still have diamine been bis(phenolate)limited [28], probably ligands [ 30due]. Several to their examplestendency were to undergo also known β-hydrogen for synthesis elimination of poly(α -olefin)sbefore subsequent with rather/rep higheated molecular insertion weights. [27,34–42]. However,We synthesisrecently reported of ultrahigh synthesis molecular of high weight molecular polymers weight by poly polymerization(α-olefin)s by of p higherolymeriαz-olefinsations of (1-decene,1-decene, 1-dodecene, 1-dodecene 1-tetradecene,, 1-hexadecene, etc.) and still 1- haveoctadecene been limited by Cp*TiCl [28], probably2(O-2,6-iPr due2C6 toH3 their)–MAO tendency catalyst to[28] undergo, andβ -hydrogenthe Mn values elimination in the before resultant subsequent polymers/repeated were insertion. higher than those prepared by [MeWe2Si(C recently5Me4)(N reportedtBu)]TiCl synthesis2 and Cp of2ZrCl high2 molecular(Table 1)weight [28]. poly(Moreover,α-olefin)s Cp*TiMe by polymerizations2(O-2,6-iPr2C6H3) i of(1 1-decene,)–[Ph3C][B(C 1-dodecene,6F5)4] (borate) 1-hexadecene, catalyst showed and 1-octadecenethe higher catalytic by Cp*TiCl activities2(O-2,6-, affordingPr2C6H3 )–MAOultrahigh catalystmolecular [28], weight and the poly(1Mn -valuesoctene)s in and the poly(1 resultant-dodecene)s polymers (Table were 1) higher [28]. On than the those other preparedhand, we byalso t i [Mereported2Si(C5Me that4)(N 1-Bu)]TiClhexene polymerization2 and Cp2ZrCl 2by(Table 1–borate1)[ 28catalyst]. Moreover, proceeded Cp*TiMe in a quasi2(O-2,6--livingPr2 Cmanner6H3) 6 (1)–[Phunder3 C][B(Ccertain6 Fconditions5)4] (borate) to afford catalyst ultrahigh showed molecular the higher weight catalytic poly(1 activities,-hexene)s aff (ordingMn ≥ 1.0 ultrahigh–1.9 × 10 ) molecular[33]. Therefore, weight we poly(1-octene)s herein present and synthesis poly(1-dodecene)s of high molecular (Table 1weight)[ 28]. polymers On the other by polymerizations hand, we also reportedof 1-decene that 1-hexene (DC), 1- polymerizationdodecene (DD) by, and1–borate 1-tetradecene catalyst proceeded(TD) with inlow a quasi-living PDI (Mw/M mannern) values under using 6 certain1-borate conditions catalyst toin the afford presence ultrahigh of Al molecular cocatalyst weight (Scheme poly(1-hexene)s 1). (Mn 1.0–1.9 10 )[33]. ≥ × Therefore, we herein present synthesis of high molecular weight polymers by polymerizations of i 1-deceneTable (DC), 1. 1-dodecenePolymerization (DD), of 1 and-octene 1-tetradecene (OC) and 1- (TD)dodecene with (DD), low PDIusing (M Cp*TiXw/Mn)2(O values-2,6- Pr using2C6H31) -borate[X = catalystCl, in Me the (1 presence)], [Me2Si(C of5Me Al4 cocatalyst)(NtBu)]TiCl (Scheme2, Cp2ZrCl1).2—cocatalyst systems [28]. a b c n d w n d catalyst α-olefin cocatalyst time/min TON Activity i M M /M Table 1. Polymerizationi of 1-octene (OC) and 1-dodecene (DD), using Cp*TiX2(O-2,6- Pr2C6H3) [X = Cl, Cp*TiCl2(O-2,6- Pr2C6H3) t OC MAO 30 9950 a 2240 501000 1.42 Me (1)], [Me2Si(Ci 5Me4)(N Bu)]TiCl2, Cp2ZrCl2—cocatalyst systems [28]. Cp*TiCl2(O-2,6- Pr2C6H3) DD MAO 30 4120 1390 525000 1.35 i b c d d Cp*TiMeCatalyst2(O-2,6- Pr2C6H3α)-Olefin OC Cocatalystborate Time/min20 TON7080 Activity2380 Mn1970000M w/Mn 2.04 i i Cp*TiMeCp*TiCl2(O-2,6-2(O-Pr2,62C-6PrH32)C6H3) OCDD MAOborate 3020 99503730 22401880 5010001320000 1.42 1.99 Cp*TiCl (O-2,6-iPr Ct H ) DD MAO 30 4120 1390 525000 1.35 [Me2Si(C2 5Me4)(N2 Bu)]TiCl6 3 2 OC MAO 30 4810 1080 292000 1.64 i OC borate 20 7080 2380 1970000 2.04 Cp*TiMe2(O-2,6- Pr2Ct 6H3) [Me2Si(C5Me4i)(N Bu)]TiCl2 Cp*TiMe2(O-2,6- Pr2C6H3) DDDD borateMAO 2030 37302060 1880690 1320000351000 1.99 1.33 t [Me2Si(C5MeCp4)(N2ZrClBu)]TiCl2 2 OCOC MAOMAO 3030 481021300 10804790 2920004100 1.64 1.55 t [Me2Si(C5Me4)(N Bu)]TiCl2 DD MAO 30 2060 690 351000 1.33 Cp2ZrCl2 DD MAO 30 15400 5190 5000 1.57 Cp2ZrCl2 OC MAO 30 21300 4790 4100 1.55 a ConditionsCp2ZrCl2 (MAO cocatalyst):DD Complex MAO 1.0 μmol, 30 α-olefin 15400 5.0 mL, d- 5190MAO (prepared 5000 by removing 1.57 a Conditionstoluene and (MAO AlMe cocatalyst):3 from ordinary Complex MAO) 1.0 µmol, 2.0α mmol,-olefin 5.025 mL,°C; C d-MAOonditions (prepared (borate by cocata removinglyst): toluene Complex and 1 AlMe3 from ordinary MAO) 2.0 mmol, 25 ◦C; Conditionsi (borate cocatalyst): Complex 1 0.25 µmol, olefin 5.0b mL, 0.25 µmol,i olefin 5.0 mL, −30 °C, Al Bu3/[Ph3C][B(Cb6F5)4]/Ti = 500/3.0/1.0 (molar ratio). TON 30 ◦C, Al Bu3/[Ph3C][B(C6F5)4]/Ti = 500/3.0/1.0 (molar ratio). TON (turnover number) = (mmol of α-olefin reacted)− (turnover/(mmol-Ti). number)c Activity = (mmol= kg-polymer of α-olefin/mol-Ti reacted)/(mmolh. d Gel-permeation-Ti). c chromatographyActivity = kg- (GPC)polymer/mol data THF-Ti·h vs.. d · polystyreneGel-permeation standards. chromatography (GPC) data THF vs. polystyrene standards. Scheme 1. Polymerization of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) using Scheme 1. Polymerizationi of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) using Cp*TiMe2(O-2,6- Pr2C6H3)(1)–[Ph3C][B(C6F5)4] catalyst in the presence of Al cocatalyst. Cp*TiMe2(O-2,6-iPr2C6H3) (1)–[Ph3C][B(C6F5)4] catalyst in the presence of Al cocatalyst.