Syndiotactic styrene-butadiene block copolymers synthesized with CpTiX3/MAO (Cp = C5H5, X = Cl, F; Cp = C5Me5, X = Me) and TiXn/MAO (n = 3, X = acac; n = 4, X = O-tert-Bu)

Stereoselectivity and Chemoselectivity in Ziegler−Natta Polymerizations of Conjugated Dienes. 1. Monomers with Low-Energy s-Cis η4 Coordination

“…The relative energies of the diastereoisomeric monomer free intermediates of Figure 1, and the low-energy reaction paths just described are in qualitative agreement with several experimental facts. In particular, systems based on CpTiX 3 (X ) Cl, [44][45] F, 45 CH 3 , 45 OR 46 ) polymerize butadiene to products containing prevailingly 1,4 units (∼85%) and 1,2 units (∼10%), whose ratio is in qualitative agreement with the energy difference between the monomer free structures 1a and 1b and between the insertion transition states 4a and 4b. Moreover, the small energy difference between intermediates 1a and 1b as well as transition states 4a and 4b, which lead to 1,4 and 1,2 enchainments, respectively, could be responsible of the strong dependence of chemoselectivity on the kind of diene monomer.…”

Thin‐film nanostructure and polymer architecture in semicrystalline syndiotactic poly(p‐methylstyrene)–(cis‐1,4‐polybutadiene) multiblock copolymers

“…The r 1 and r 2 values ( r 1 = k 11 / k 12 , r 2 = k 22 / k 21 , M 1 = p MS and M 2 = B) were determined from NMR data using Eqns (4) and (5), following the procedure previously reported for styrene–butadiene copolymerization catalysed by half‐sandwich titanocene: …”

“…Several strategies have been conceived for the synthesis of di‐ and multiblock styrenic copolymers with conjugated dienes: (i) the stepwise living polymerization of the two monomers; (ii) the multiple coupling of pre‐polymerized segments; and (iii) the one‐pot copolymerization of the monomers . The first two methods allow precise syntheses while the third is most attractive for the simplicity of the procedure but needs catalytic systems suitable for the selective sequential insertion of the monomers.…”

“…The first two methods allow precise syntheses while the third is most attractive for the simplicity of the procedure but needs catalytic systems suitable for the selective sequential insertion of the monomers. Copolymers of S with isoprene were synthesized using the half‐sandwich titanium pre‐catalyst ( η 5 ‐C 5 Me 5 )Ti(CH 3 ) 3 , activated with [(C 2 H 5 ) 3 NH][B(C 6 F 5 ) 4 ] or B(C 6 F 5 ) 3 , or ( η 5 ‐C 5 H 5 )TiX 3 (X = Cl, F; Cp = C 5 Me 5 , X = Me) and ( η 5 ‐C 5 H 5 )Ti( κ 2 ‐MBMP)Cl (MBMP = 2,2′‐methylenebis(6‐ tert ‐butyl‐4‐methylphenoxo)) complexes, activated by methylalumoxane (MAO). Recently, half‐sandwich metal complexes of lutetium and scandium have been reported .…”

Synthesis and characterization of cis‐polybutadiene‐block‐syn‐polystyrene copolymers with a cyclopentadienyl titanium trichloride/modified methylaluminoxane catalyst

“…Preliminary attempts to synthesize cis ‐polybutadiene ( cis ‐PB)/ syn ‐PS random or block copolymers were carried out by Zambelli and coworkers with methylaluminoxane (MAO)‐activated cyclopentadienyl titanium trichloride (CpTiCl 3 ),12 which is well known to be an effective catalyst not only for syndiospecific ST polymerizations13, 14 but also for cis‐specific BD polymerizations 15–17. However, after an extensive characterization of the copolymer products, it was found that only a mixture of an atactic polystyrene ( ata ‐PS), possibly produced by MAO‐initiated cationic polymerization, and a cis ‐1,4‐PB was formed, despite the expected stereoregular ST–BD copolymers 18. Very recently, they reported interesting results for the preparation of ST–BD copolymers exhibiting relatively high crystalline melting temperatures ( T m 's) ranging from 170 to 220 °C, which indicated the presence of crystallizable syn ‐PS sequences 19, 20.…”