Syndiotactic–Atactic Stereoblock Polystyrene Obtained with a Hapto-Flexible Catalyst

Abstract

Half-titanocene (CpCH2CH2OCH3)­TiCl3 (1), (Cp = cyclopentadienyl), activated by methylaluminoxane (MAO), has been tested in the polymerization of styrene in a suitable range of temperatures, obtaining a new material consisting of syndiotactic–atactic stereoblocks of polystyrene. The monoanionic bidentate ancillary ligand of the titanium based catalyst, consisting of a cyclopentadienyl bearing an alkyl ether, is a hapto-flexible ligand because the ether group can either be coordinated or not to the metal, depending on reaction temperature. Thus, the ether group can give rise to two possible catalytic sites: (i) syndiospecific, when the ether group is not coordinated to the metal center, and (ii) aspecific, when it is coordinated to titanium. Consequently, it produces polymer chains having syndiotactic and atactic stereoblocks. In fact, in the range of temperature considered (0–19 °C), syndiotactic polystyrene was produced at 19 °C, atactic polystyrene at 0 and 5 °C, and syndiotactic–atactic stereoblock polystyrene at 10 and 15 °C.

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

“…Syndiotactic polystyrene (sPS) has become a very important engineering plastic because of its high melting point ( T m = 270 °C), rapid crystallization ability, low dielectric constant, and excellent resistance to heat and chemicals. − This inexpensive polymer is an attractive material for a large number of industrial applications because of its unique combination of valuable properties. ,− In 1986, sPS was discovered first by Ishihara at Idemitsu by using unlinked half-sandwich titanium catalysts . After that, a large number of titanium analogues generally formulated as [LTiX 3 ] have been extensively investigated, where L could be any of cyclopentadienyl-related ligands and X is a halogen or alkoxyl group .…”

Stereoselective Copolymerization of Styrene with para-Substituted Styrenes Catalyzed by Half-Titanocenes: An Experimental and Computational Study

“…As previously reported, ( 1 ) and ( 2 ), activated by MAO, are highly syndiospecific single-site catalysts capable of polymerizing both styrene and p- methylstyrene. − On the contrary, in the polymerization of p- chlorostyrene, catalyst ( 1 ) is stereospecific at room temperature and at high monomer concentrations, whereas catalyst ( 2 ) produces only atactic polymer . Compounds ( 1 ) and ( 2 ), activated by MAO, show a different behavior also in both ethene–cyclopentene copolymerization and butadiene homopolymerization. , …”

“…As for Ti oxidation states, we assumed Ti(IV) for structures involving catalyst (1) 16 and Ti(III) for structures involving catalysts (2) 17 and Cp. 34−37 Geometries reported in Figure 3 are representative of all insertions for each catalyst.…”

“…1 H NMR, 13 C NMR, and elemental analyses were in agreement with the data reported. 16,17 2.3. Copolymerizations of Styrene with p-Methylstyrene or p-Chlorostyrene in the Presence of Catalytic Systems (1)/MAO and (2)/MAO.…”

Engineering of Syndiotactic and Isotactic Polystyrene-Based Copolymers via Stereoselective Catalytic Polymerization

“…However, they are principally represented by graft or diblock copolymers, synthezised through multi-step processes (see Section 6 for details); there are very few examples of stereoblocks PS copolymers obtained through a one-pot procedure involving a single catalytic system. The most relevant example is a multiblock sPS- co -aPS synthesized by Longo et al through an elegant process involving the hapto-flexible catalyst 17 [ 88 ]. Depending on the temperature, the ether group of the ligand is coordinated to the titanium or not, affording different active species: a syndiospecific one in which the ether function is claimed not to be coordinated (around 19 °C), and an aspecific one with the coordinated ether (0–5 °C).…”