This review summarizes recent results for ethylene/styrene copolymerization using half-titanocenes containing anionic donor ligands, Cp’TiX 2(Y) (X = halogen, alkyl; Y = aryloxo, ketimide etc.)–cocatalyst systems. The product composition, the styrene incorporation and microstructures in the resultant copolymers are highly influenced by the anionic donor employed. A methodology for an exclusive synthesis of the copolymers even under high temperature and high styrene concentrations has been introduced on the basis of a proposed catalytically-active species in this catalysis.
Bolton, P.D.; Mountford, P. Transition metal imido compounds as Ziegler-Natta olefin polymerisation catalysts. Adv. Synth. Catal.？2005, 347, 355–366, doi:10.1002/adsc.200404267.
[9]
Gladysz, J.A. Frontiers in Metal-Catalyzed Polymerization; ACS Publication: Washington, DC, USA, 2000; p. 100.
[10]
Ittel, S.D.; Johnson, L.K.; Brookhart, M. Late-metal catalysts for ethylene homo- and copolymerization. Chem. Rev.？2000, 100, 1169–1203, doi:10.1021/cr9804644.
[11]
Alt, H.G.; K？ppl, A. Effect of the nature of metallocene complexes of group iv metals on their performance in catalytic ethylene and propylene polymerization. Chem. Rev.？2000, 100, 1205–1221, doi:10.1021/cr9804700.
[12]
Chen, E.Y.-X.; Marks, T.J. Cocatalysts for metal-catalyzed olefin polymerization: activators, activation processes, and structure-activity relationships. Chem. Rev.？2000, 100, 1391–1434, doi:10.1021/cr980462j.
[13]
Coates, G.W.; Hustad, P.D.; Reinartz, S. Catalysts for the living insertion polymerization of alkenes: access to new polyolefin architectures using Ziegler-Natta chemistry. Angew. Chem. Int. Ed.？2002, 41, 2236–2257, doi:10.1002/1521-3773(20020703)41:13<2236::AID-ANIE2236>3.0.CO;2-3.
[14]
Domski, G.J.; Rose, J.M.; Coates, G.W.; Bolig, A.D.; Brookhart, M. Living alkene polymerization: New methods for the precision synthesis of polyolefins. Prog. Polym.Sci.？2007, 32, 30–92, doi:10.1016/j.progpolymsci.2006.11.001.
[15]
Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. Nonbridged half-metallocenes containing anionic ancillary donor ligands: New promising candidates as catalysts for precise olefin polymerization. J. Mol.Catal. A？2007, 267, 1–29, doi:10.1016/j.molcata.2006.11.006.
[16]
Stephan, D.W. The road to early-transition-metal phosphinimide olefin polymerization catalysts. Organometallics？2005, 24, 2548–2560, doi:10.1021/om050096b.
[17]
Nomura, K. Half-titanocenes containing anionic ancillary donor ligands as promising new catalysts for precise olefin polymerisation. Dalton Trans.？2009, 8811–8823, doi:10.1039/b910407k.
[18]
Nomura, K.; Liu, J. Half-titanocenes for precise olefin polymerisation: Effects of ligand substituents and some mechanistic aspects. Dalton Trans.？2011, 40, 7666–7682. and references including list of reported complexes are cited therein.
[19]
Soga, K.; Lee, D.H.; Yanagihara, H. Copolymerization of ethylene with styrene using the catalyst system composed of Solvay-type TiCl3 and Cp2Ti(CH3)2. Polym. Bull.？1988, 20, 237–241.
[20]
Mani, P.; Burns, C.M. Homo- and copolymerization of ethylene and styrene using titanium trichloride (AA)/methylaluminoxane. Macromolecules？1991, 24, 5476–5477, doi:10.1021/ma00019a042.
[21]
Cheung, Y.W.; Guest, M.J. Modern Styrenic Polymers: Polystyrenes and Styrenic Copolymers; Scheirs, J., Priddy, D.B., Eds.; John Wiley & Sons Ltd.: Chichester, UK, 2003; p. 605.
[22]
Guest, M.J.; Cheung, Y.W.; Diehl, C.F.; Hoenig, S.M. Metallocene-Based Polyolefins; Scheirs, J., Kaminsky, W., Eds.; John Wiley & Sons Ltd.: Chichester, UK, 2000; Volume 2, p. 271.
[23]
Chen, H.; Guest, M.J.; Chum, S.; Hiltner, A.; Baer, E. Classification of ethylene-styrene interpolymers based on comonomer content. J. Appl. Polym. Sci.？1998, 70, 109–119, doi:10.1002/(SICI)1097-4628(19981003)70:1<109::AID-APP11>3.0.CO;2-2.
Cheung, Y.W.; Guest, M.J. A study of the blending of ethylene-styrene copolymers differing in the copolymer styrene content: Miscibility considerations. J. Polym. Sci., Part B？2000, 38, 2976–2987, doi:10.1002/1099-0488(20001115)38:22<2976::AID-POLB130>3.0.CO;2-5.
[26]
Ishihara, N.; Seimiya, T.; Kuramoto, M.; Uoi, M. Synthesis and properties of polystyrene with new stereoregularity. Polym. Prepr.Jpn.？1986, 35, 240.
[27]
Ishihara, N.; Seimiya, T.; Kuramoto, M.; Uoi, M. Crystalline syndiotactic polystyrene. Macromolecules？1986, 19, 2464–2465, doi:10.1021/ma00163a027.
[28]
Ishihara, N.; Seimiya, T.; Kuramoto, M.; Uoi, M. Stereospecific polymerization of styrene giving the syndiotactic polymer. Macromolecules？1988, 21, 3356–3360, doi:10.1021/ma00190a003.
Zambelli, A.; Longo, P.; Pellecchia, C.; Grassi, A. Hydrogen abstraction and regiospecific insertion in syndiotactic polymerization of styrene. Macromolecules？1987, 20, 2035–2037, doi:10.1021/ma00174a063.
[31]
Zambelli, A.; Oliva, L.; Pellecchia, C. Soluble catalysts for syndiotactic polymerization of styrene. Macromolecules？1989, 22, 2129–2130, doi:10.1021/ma00195a021.
[32]
Ready, T.E.; Day, R.O.; Chien, J.C.W.; Rausch, M.D. (η5-Indenyl)trichlorotitanium. An improved syndiotactic polymerization catalyst for styrene. Macromolecules？1993, 26, 5822–5283, doi:10.1021/ma00073a046.
[33]
Chien, J.C.W. New and improved catalysts for syndiotactic polystyrene. Metallocenes？1996, 96, 223–237.
[34]
Kaminsky, W.; Lenk, S.; Scholz, V.; Roesky, H.W.; Herzog, A. Fluorinated half-sandwich complexes as catalysts in syndiospecific styrene polymerization. Macromolecules？1997, 30, 7647–7650, doi:10.1021/ma970601j.
[35]
Wu, Q.; Ye, Z.; Lin, S. Syndiotactic polymerization of styrene with cyclopentadienyl-tribenzyloxytitanium/methylaluminoxane catalyst. Macromol. Chem. Phys.？1997, 198, 1823–1828, doi:10.1002/macp.1997.021980611.
[36]
Tomotsu, N.; Kuramoto, M.; Takeuchi, M.; Maezawa, H. The catalyst for syndiotactic-specific poliymerization of styrene. Metallocenes？1996, 96, 179–196.
[37]
Tomotsu, N.; Ishihara, N. Novel catalysts for syndiospecific polymerization of styrene. Catal. Surv. Jpn.？1997, 1, 97–110.
[38]
Tomotsu, N.; Ishihara, N.; Newman, T.H.; Malanga, M.T. Syndiospecific polymerization of styrene. J. Mol. Catal. A？1998, 128, 167–190, doi:10.1016/S1381-1169(97)00171-4.
[39]
Pellechia, C.; Grassi, A. Syndiotactic-specific polymerization of styrene: Catalyst structure and polymerization mechanism. Top. Catal.？1999, 7, 125–132, doi:10.1023/A:1019120002102.
[40]
Metallocene-Based Polyolefins; Scheirs, J., Kaminsky, W., Eds.; Wiley: Chichester, UK, 2000; Volume 2, p. 568.
[41]
Longo, P.; Grassi, A.; Oliva, L. Copolymerization of styrene and ethylene in the presence of different syndiospecific catalysts. Makromol. Chem.？1990, 191, 2387–2396, doi:10.1002/macp.1990.021911016.
[42]
Pellecchia, C.; Pappalardo, D.; D’Arco, M.; Zambelli, A. Alternating ethylene-styrene copolymerization with a methylaluminoxaiie-free half-titanocene catalyst. Macromolecules？1996, 29, 1158–1162, doi:10.1021/ma951152v.
[43]
Oliva, L.; Mazza, S.; Longo, P. Copolymerization of ethylene and styrene with monocyclopentadienyltitanium trichloride/ methylalumoxane catalyst. Macromol. Chem. Phys.？1996, 197, 3115–3122, doi:10.1002/macp.1996.021971005.
[44]
Xu, G.; Lin, S. Titanocene-Methylaluminoxane Catalysts for copolymerization of styrene and ethylene: Synthesis and characterization of styrene-ethylene copolymers. Macromolecules？1997, 30, 685, doi:10.1021/ma960792a.
[45]
Lee, D.H.; Yoon, K.B.; Kim, H.J.; Woo, S.S.; Noh, S.K. Copolymerization of styrene and ethylene with mononuclear and dinuclear half-titanocenes. J. Appl.Polym. Sci.？1998, 67, 2187–2198, doi:10.1002/(SICI)1097-4628(19980328)67:13<2187::AID-APP9>3.0.CO;2-A.
[46]
Ewart, S.W.; Baird, M.C. Olefin polymerization by pentamethylcyclopentadienyl trimethyltitanium, Cp*TiMe3. Topics in Catalysis？1999, 7, 1–8, doi:10.1023/A:1019107632144.
[47]
Baird, M.C. Carbocationic alkene polymerizations initiated by organotransition metal complexes: an alternative, unusual role for soluble Ziegler-Natta catalysts. Chem. Rev.？2000, 100, 1471–1478, doi:10.1021/cr990252m.
[48]
Gillis, D.J.; Tudoret, M.-J.; Baird, M.C. Novel arene complexes of titanium(IV), zirconium(IV), and hafnium(IV). J. Am. Chem. Soc.？1993, 115, 2543–2545, doi:10.1021/ja00059a079.
[49]
Quyoum, R.; Wang, Q.; Tudoret, M.-J.; Baird, M.C. 5-C5Me5TiMe3B(C6F5)3: A carbocationic olefin polymerization initiator masquerading as a Ziegler-Natta catalyst. J. Am. Chem. Soc.？1994, 116, 6435–6436, doi:10.1021/ja00093a054.
[50]
Wang, Q.; Quyoum, R.; Gillis, D.J.; Tudoret, M.-J.; Jeremic, D.; Hunter, B.K.; Baird, M.C. Ethylene, styrene, and α-methylstyrene polymerization by mono(pentamethylcyclopentadienyl) (Cp*) complexes of titanium, zirconium, and hafnium: roles of cationic complexes of the type [Cp*MR2]+ (R = alkyl) as both coordination polymerization catalysts and carbocationic polymerization initiators. Organometallics？1996, 15, 693–703, doi:10.1021/om9501945.
[51]
In this catalyst system with Cp*TiMe2(μ-Me)B(C6F5)3 generated from Cp*TiMe3 and B(C6F5)3 [46,47,48,49], styrene polymerization took place in both cationic and coordination insertion manners, to give atactic polystyrene and syndiotactic polystyrene, respectively. The cationic polymerization of isobutene also took place, and 1-hexene polymerization afforded polymer with a broad molecular weight distribution. Since the styrene homopolymerization also took place only with borate, MAO in a cationic manner, it might be difficult to estimate the catalytic activity with titanium catalyst.
[52]
Nomura, K.; Komatsu, T.; Imanishi, Y. Syndiospecific styrene polymerization and efficient ethylene/styrene copolymerization catalyzed by (cyclopentadienyl)(aryloxy)titanium(IV) complexes - MAO system. Macromolecules？2000, 33, 8122–8124, doi:10.1021/ma0011284.
[53]
Nomura, K.; Okumura, H.; Komatsu, T.; Naga, N. Ethylene/styrene copolymerization by various (cyclopentadienyl)(aryloxy)-titanium(IV) complexes-MAO catalyst systems. Macromolecules？2002, 35, 5388–5395, doi:10.1021/ma0200773.
[54]
Nomura, K.; Zhang, H.; Byun, D.-J. Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes-MAO catalyst system. J. Polym. Sci. Part A？2008, 46, 4162–4174, doi:10.1002/pola.22765.
[55]
Nomura, K.; Suzuki, N.; Kim, D.H.; Kim, H.J. Effect of cocatalyst in ethylene/styrene copolymerization by aryloxo-modified half-titanocene-cocatalyst systems for exclusive synthesis of copolymers at high styrene concentrationsa. Macromol. Reac. Eng.？2012, 6, 351–356, doi:10.1002/mren.201200024.
[56]
Nomura, K.; Pracha, S.; Phomphrai, K.; Katao, S.; Kim, D.H.; Kim, H.J.; Suzuki, N. Synthesis and structural analysis of phenoxy-substituted half-titanocenes with different anionic ligands, Cp*TiX(Y)(O-2,6-iPr2C6H3): Effect of anionic ligands (X,Y) in ethylene/styrene copolymerization. J. Mol. Catal. A？2012, 365, 136–145, doi:10.1016/j.molcata.2012.08.022.
[57]
Zhang, H.; Nomura, K. Living copolymerization of ethylene with styrene catalyzed by (cyclopentadienyl)(ketimide)titanium(iv) complex-MAO catalyst system. J. Am. Chem. Soc.？2005, 127, 9364–9365, doi:10.1021/ja052198z.
[58]
Zhang, H.; Nomura, K. Living copolymerization of ethylene with styrene catalyzed by (cyclopentadienyl)(ketimide)titanium(IV) complex-MAO catalyst system: effect of anionic ancillary donor ligand. Macromolecules？2006, 39, 5266–5274.
[59]
Kretschmer, W.P.; Dijkhuis, C.; Meetsma, A.; Hessen, B.; Teuben, J.H. A highly efficient titanium-based olefin polymerisation catalyst with a monoanionic iminoimidazolidide p-donor ancillary ligand. Chem. Commun.？2002, 608–609.
[60]
Wang, Q.; Lam, P.; Zhang, Z.; Yamashita, G.; Fan, L. Ethylene styrene interpolymers with double reverse styrene incorporation. US 6579961 B1, 17 June 2003.
[61]
Nomura, K.; Fukuda, H.; Katao, S.; Fujiki, M.; Kim, H.J.; Kim, D.H.; Zhang, S. Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands-MAO catalyst systems. Dalton Trans.？2011, 40, 7842–7849.
[62]
Nomura, K.; Fukuda, H.; Katao, S.; Fujiki, M.; Kim, H.J.; Kim, D.H.; Saeed, I. Olefin polymerization by half-titanocenes containing η2-pyrazolato ligands-MAO catalyst systems. Macromolecules？2011, 44, 1986–1998, doi:10.1021/ma200018z.
[63]
Nomura, K.; Fukuda, H.; Apisuk, W.; Trambitas, A.G.; Kitiyanan, B.; Tamm, M. Ethylene copolymerization by half-titanocenes containing imidazolin-2-iminato ligands-MAO catalyst systems. J. Mol. Catal. A？2012, 363-364, 501–511, doi:10.1016/j.molcata.2012.08.001.
[64]
Stevens, J.C.; Timmers, F.J.; Wilson, D.R.; Schmidt, G.F.; Nickias, P.N.; Rosen, R.K.; Knight, G.W.; Lai, S.Y. Constrained geometry addition polymerization catalysts, processes for their preparation, precursors. EP 0416815 A2, 13 March 1991.
[65]
Timmers, F.J. Olefin polymers formed by use of constrained geometry addition polymerization catalysts. USP 6670432 B1, 30 December 2003.
[66]
Arriola, D.J.; Bokota, M.; Campbell, R.E., Jr.; Klosin, J.; LaPointe, R.E.; Redwine, O.D.; Shankar, R.B.; Timmers, F.J.; Abboud, K.A. Penultimate effect in ethylene-styrene copolymerization and the discovery of highly active ethylene-styrene catalysts with increased styrene reactivity. J. Am. Chem. Soc.？2007, 129, 7065–7076.
[67]
Sernetz, F.G.; Mülhaupt, R.; Waymouth, R.M. Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(MeCp)(N-tert-butyl)TiC12 /methylaluminoxane Ziegler-Natta catalysts. Macromol. Chem. Phys.？1996, 197, 1071–1083, doi:10.1002/macp.1996.021970325.
[68]
Sernetz, F.G.; Mülhaupt, R.; Amor, F.; Eberle, T.; Okuda, J. Copolymerization of ethene with styrene using different methylalumoxane activated half-sandwich complexes. J. Polym. Sci. Part A？1997, 35, 1571–1578, doi:10.1002/(SICI)1099-0518(199706)35:8<1571::AID-POLA26>3.0.CO;2-3.
[69]
Sukhova, T.A.; Panin, A.N.; Babkina, O.N.; Bravaya, N.M. Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (M = Ti, X = CH3, M = Zr, X = iBu) in copolymerization of ethylene with styrene. J. Polym. Sci., Part A？1999, 37, 1083–1093, doi:10.1002/(SICI)1099-0518(19990415)37:8<1083::AID-POLA5>3.0.CO;2-G.
[70]
Xu, G. Copolymerization of ethylene with styrene catalyzed by the [η1:η5-tert-butyl(dimethylfluorenylsilyl)amido]methyltitanium “cation”. Macromolecules？1998, 31, 2395–2402, doi:10.1021/ma971480q.
[71]
Kamigaito, M.; Lal, T.K.; Waymouth, R.M. Olefin polymerization with Me4Cp-amido complexes with electron-withdrawing groups. J. Polym. Sci. Part A？2000, 38, 4649–4660, doi:10.1002/1099-0518(200012)38:1+<4649::AID-POLA40>3.0.CO;2-#.
[72]
Nomura, K.; Okumura, H.; Komatsu, T.; Naga, N. Imanishi, YEffect of ligand in ethylene/styrene copolymerization by [Me2Si(C5Me4)(NR)]TiCl2 (R = tert-Bu, cyclohexyl) and (1,3-Me2C5H3)TiCl2(O-2,6-iPr2C6H3)-MAO catalyst system. J. Mol. Catal. A？2002, 190, 225–234, doi:10.1016/S1381-1169(02)00223-6.
[73]
Guo, N.; Li, L.; Marks, T.J. Bimetallic catalysis for styrene homopolymerization and ethylene-styrene copolymerization. Exceptional comonomer selectivity and insertion regiochemistry. J. Am. Chem. Soc.？2004, 126, 6542–6543, doi:10.1021/ja048761f.
[74]
Li, H.; Marks, T.J. Nuclearity and cooperativity effects in binuclear catalysts and cocatalysts for olefin polymerization. Proc. Natl. Acad. Sci. USA？2006, 103, 15295–15302, doi:10.1073/pnas.0603396103.
[75]
Guo, N.; Stern, C.L.; Marks, T.J. Bimetallic effects in homopolymerization of styrene and copolymerization of ethylene and styrenic comonomers: Scope, kinetics, and mechanism. J. Am. Chem. Soc.？2008, 130, 2246–2261, doi:10.1021/ja076407m.
Rodrigues, A.-S.; Carpentier, J.-F. Groups 3 and 4 single-site catalysts for styrene-ethylene and styrene-α-olefin copolymerization. Coord. Chem. Rev.？2008, 252, 2137–2154, doi:10.1016/j.ccr.2007.11.023.
[78]
Nomura, K. Syndiotactic Polystyrene—Synthesis, Characterization, Processing, and Applications; Schellenberg, J., Ed.; Wiley-VCH: NJ, USA, 2010; pp. 60–91.
[79]
Nomura, K. Syndiospecific styrene polymerization and ethylene/styrene copolymerization using half-titanocenes: ligand effects and some new mechanistic aspects. Catal. Surv. Asia？2011, 14, 33–49, doi:10.1007/s10563-010-9086-4.
[80]
Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.; Imai, A. Synthesis of various nonbridged titanium(IV) cyclopentadienyl-aryloxy complexes of the type CpTi(OAr)X2 and their use in the catalysis of alkene polymerization. Important roles of substituents on both aryloxy and cyclopentadienyl groups. Organometallics？1998, 17, 2152–2154, doi:10.1021/om980106r.
[81]
Nomura, K.; Oya, K.; Komatsu, T.; Imanishi, Y. Effect of the cyclopentadienyl fragment on monomer reactivities and monomer sequence distributions in ethylene/α-olefin copolymerization by a nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) complex-MAO catalyst system. Macromolecules？2000, 33, 3187–3189, doi:10.1021/ma000317j.
[82]
Nomura, K.; Oya, K.; Imanishi, Y. Ethylene/α-olefin copolymerization by various nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) complexes -MAO catalyst system. J. Mol. Catal.A？2001, 174, 127–140, doi:10.1016/S1381-1169(01)00196-0.
[83]
Kakinuki, K.; Fujiki, M.; Nomura, K. Copolymerization of ethylene with α-olefins containing various substituents catalyzed by half-titanocenes: Factors affecting the monomer reactivities. Macromolecules？2009, 42, 4585–4595, doi:10.1021/ma900576v.
[84]
According to the described experimental procedures (including the results regarding Tg values of the resultant polymers) [60], it is not yet clear whether or not the styrene contents reported here may include atactic/syndiotactic polystyrene. The Mw/Mn values in certain polymerization runs also seemed somewhat broad.
[85]
Related examples in ethylene/1-hexene copolymerization: Reybuck, S.E.; Meyer, A.; Waymouth, R.M. Copolymerization behavior of unbridged indenyl metallocenes: Substituent effects on the degree of comonomer incorporation. Macromolecules？2002, 35, 637–643, doi:10.1021/ma011517d.
[86]
Nomura, K.; Fujita, K.; Fujiki, M. Olefin polymerization by (cyclopentadienyl)(ketimide)-titanium(IV) complexes of the type, Cp’TiCl2(N = CtBu2)-methylaluminoxane (MAO) catalyst systems. J. Mol. Catal. A？2004, 220, 133–144, doi:10.1016/j.molcata.2004.06.010.
[87]
Byun, D.-J.; Fudo, A.; Tanaka, A.; Fujiki, M.; Nomura, K. Effect of cyclopentadienyl and anionic ancillary ligand in syndiospecific styrene polymerization catalyzed by nonbridged half-titanocenes containing aryloxo, amide, and anilide ligands - cocatalyst systems. Macromolecules？2004, 37, 5520–5530, doi:10.1021/ma049549z.
[88]
Nomura, K.; Fujita, K.; Fujiki, M. Effects of cyclopentadienyl fragment in ethylene, 1-hexene, and styrene polymerizations catalyzed by half-titanocenes containing ketimide ligand of the type, Cp’TiCl2(N = CtBu2). Catal. Commun.？2004, 5, 413–417, doi:10.1016/j.catcom.2004.05.005.
[89]
Mahanthappa, M.K.; Waymouth, R.M. Titanium-mediated syndiospecific styrene polymerizations: Role of oxidation state. J. Am.Chem. Soc.？2001, 123, 12093–12094, doi:10.1021/ja016521j.
[90]
Zhang, H.; Byun, D.-J.; Nomura, K. Tuning the active species from syndiospecific styrene polymerisation to ethylene/styrene copolymerisation by (aryloxo)(cyclopentadienyl)titanium complexes-MAO catalysts. Dalton Trans.？2007, 1802–1806, doi:10.1039/b701003f.
[91]
Nomura, K.; Tanaka, A.; Katao, S. Effect of aryloxide ligand in 1-hexene, styrene polymerization catalyzed by nonbridged half-titanocenes of the type, Cp’TiCl2(OAr) (Cp’ = C5Me5, tBuC5H4). Structural analyses for Cp*TiCl2(O-2,6-tBu2C6H3) and Cp*TiCl2(O-2,6-iPr2-4-tBuC6H2). J. Mol. Catal. A？2006, 254, 197–205, doi:10.1016/j.molcata.2006.03.030.
[92]
Examples for a mechanistic study concerning both styrene polymerization (and propylene/styrene copolymerization), see references [89,94,95].
[93]
Nomura, K.; Fudo, A. Syndiospecific styrene polymerization by (tert-BuC5H4)TiCl2(O-2,6-iPr2C6H3) - borate catalyst system. Catal. Lett.？2003, 4, 269–274.
[94]
Grassi, A.; Zambelli, A.; Laschi, F. Reductive decomposition of cationic half-titanocene(IV) complexes, precursors of the active species in syndiospecific styrene polymerization. Organometallics？1996, 15, 480–482, doi:10.1021/om950666f.
[95]
Minieri, G.; Corradini, P.; Guerra, G.; Zambelli, A.; Cavallo, L. A Theoretical study of syndiospecific styrene polymerization with Cp-based and Cp-free titanium catalysts. 2. Mechanism of chain-end stereocontrol. Macromolecules？2001, 34, 5379–5385, doi:10.1021/ma002163d.
